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Drugs 45 (2): 232-258, 1993 0012-6667/93/0002-0232/$l 3.50/0 © Adis International Limited. All rights reserved. Carvedilol A Review of its Pharmacodynamic and Pharmacokinetic Properties, and Therapeutic Efficacy Donna McTavish, Deborah Campoli-Richards and Eugene M. Sorkin Adis International Limited, Auckland, New Zealand Various sections of the manuscript reviewed by: S.A. Doggrell, Department of Pharmacology and Clinical Pharmacology, University of Auckland, Auckland, New Zealand; A.G. Dupont, Department of Internal Medicine, Academisch Ziekenhuis - Vrije Universiteit Brussel, Brussels, Belgium; R. Eggertsen, Department of Medicine, Östra Hospital, Göteborg, Sweden; W.H. Fríshman, Montefìore Medical Center, The Jack D. Weiler Hospital of the Albert Einstein College of Medicine, Bronx, New York, USA; Y. Hattori, Department of Pharmacology, Hokkaido University School of Medicine, Sapporo, Japan; J.C. Kaski, Department of Cardίological Sciences, St George's Hospital Medical School, London, England; G. Leonetti, Centro Auxologico Italiano, Istituto di Ricovero e Cura a Carattere Scientifíco, Milano, Italy; W.J. Louis, Clinical Pharmacology and Therapeutics Unit, Department of Medicine, University of Melbourne, Heidelberg, Victoria, Australia; T.O. Morgan, Department of Physiology, University of Melbourne, Heidelberg, Victoria, Australia; T. Ogîhara, Department of Geriatric Medicine, Osaka University Medical School, Osaka, Japan; B.N.C. Prichard, Department of Clinical Pharmacology, University College and Middlesex School of Medicine, University College London, London, England; E.B. Raftery, Cardiology Research Department, Northwick Park Hospital, Harrow, Middlesex, England. Contents 233 235 235 235 237 237 237 239 240 242 242 243 244 244 245 246 246 246 246 247 249 250 250 Summary 1. Pharmacodynamic Properties 1.1 Adrenoceptor Blocking Activity 1.1.1 In Vitro and In Vivo Studies 1.1.2 Human Studies 1.2 Cardiovascular Effects 1.2.1 Blood Pressure and Heart Rate 1.2.2 Peripheral Vascular Circulation 1.2.3 Myocardial Function 1.2.4 Cardioprotective and Neuroprotective Effects 1.3 Other Effects 1.4 Mechanisms of Action 2. Pharmacokinetic Properties 2.1 Absorption and Distribution 2.2 Metabolism and Elimination 2.3 Effects of Age and Disease States 3. Therapeutic Efficacy 3.1 Mild-to-Moderate Essential Hypertension 3.1.1 Noncomparative Studies, Dose Response Studies and Comparisons with Placebo 3.1.2 Comparisons with Other Antihypertensive Agents 3.1.3 Use in Combination with Other Antihypertensive Agents 3.1.4 Use in Special Patient Groups 3.2 Chronic Stable Angina Pectoris Carvedilol: A Review 251 252 252 253 Summary Synopsis 233 3.3 Congestive Heart Failure 4. Tolerability 5. Dosage and Administration 6. Place of Carvedilol in Therapy ¯i Carvedilol is a ß-adrenoceptor antagonist which also causes peripheral vasodilation primarily via a1-adrenergic blockade. Carvedilol produces its antìhypertemive effect partly by reducing total peripheral resistance by blocking a1-adrenoceplors and by preventing ß-adrenoceptor-mediated compensatory mechanisms. This combined action avoids many of the unwanted effects associated with traditional ß-blocker or vasodilator therapy. In clinical trials published to date, most of which enrolled small numbers of patients, the antihypertensive efficacy ofcarvedilol administered once daily was similar to that ofaíenolol, labetalol, pindolol propranoloί metoprolol, nìtrendipine (in elderly patients), slow release nifedipine or captopril in patients with mild-to-moderate essential hypertension. Combined therapy with carvedilol 25mg and hydrochlorothiazide 25mg, nicardipine 60mg or slow release nifedipine 20mg has an additive antihypertensίve effect. Carvedilol and atenolol at similar doses were equally effective at reducing blood pressure in patients who had previously not responded adequately to hydrochlorothiazide monoîherapy. As a result of its multiple mechanisms of action, carvedilol is suited for the management of specific groups of hypertensive patients, such as those with renal impairment. In patients with noninsulin-dependent or insulin-dependent diabetes mellitus carvedilol does not appear to affect glucose tolerance or carbohydrate metabolism. Initial studies have demonstrated that carvedilol and slow release nifedipine have similar efficacy in patients with stable angina pectoris and there is evidence that carvedilol has a beneficial haemodynamic effect in patients with congestive heart failure (NYHA class II or III) secondary to ischaemic heart disease. A postmarketing surveillance study has shown that carvedilol is generally well tolerated with only 7% (164/2226) of patients (83% of the total number received 25mg daily for 12 weeks) withdrawing from treatment because of adverse events. Vertigo, headache, bronchospasm, fatigue and skin reactions were the most common events causing withdrawal. Thus, clinical experience to date suggests that carvedilol is likely to be a valuable addition to the options currently available for treating patients with mild-to-moderate essential hypertension, and may offer particular benefit in specific populations of hypertensive patients. Pharmacodynamic Properties Racemic carvedilol is an arylethanolamine -adrenoceptor antagonist with vasodilating properties. Antagonism of -adrenoceptor-mediated responses with carvedilol (demonstrated in various animal models and in healthy volunteers) is similar in potency, but longer lasting (15 to 16 hours) than that of propranolol (12 hours), and much greater in both potency and duration of effect than that of labetalol (1.5 hours). Some studies have shown that at a dose producing ß1blocking activity, carvedilol also antagonises ß2-adrenoceptors but to a lesser extent, thus indicating weak selectivity for ß1-adrenoceptors. However, other studies have failed to show any adrenoceptor selectivity. Antagonism of α1-adrenoceptors accounts for most of the vasodilatory activity of carvedilol, although at high concentrations (>l μmol/L) antagonism of calcium channels has been observed consistently in various animal models. Although this does not appear to contribute to the antihypertensive effects of carvedilol, it may be of significance in specific vascular beds. Carvedilol exhibits no intrinsic sympathomimetic/partial agonist activity and only weak membrane-stabilising (local anaesthetic) activity. 234 Drugs 45 (2) 1993 Carvedilol has cardioprotective effects in animal models of acute myocardial infarction and is more effective in this regard than propranolol at comparable ß-blocking doses. Carvedilol also protects against neuronal damage in in vitro and in vivo models of brain ischaemia and has antiproliferative effects in vascular smooth muscle in vitro. Single oral doses of carvedilol as low as 12.5mg reduce resting and exercise blood pressure in healthy volunteers. In hypertensive patients carvedilol dose-dependently reduced mean diastolic blood pressure. Elderly hypertensive patients (aged > 65 years, baseline supine blood pressure 185/103mm Hg) respond equally well to carvedilol; a single 12.5mg dose adequately reduced mean peak supine blood pressure in many patients. Single doses of carvedilol 25mg and nitrendipine 20mg were equally effective. Carvedilol generally has little or no effect on heart rate or cardiac index in healthy volunteers; however, cardiac output was reduced in exercising hypertensive patients treated with carvedίlol, and the drug had less effect than propranolol or metoprolol on heart rate in resting or exercising hypertensive patients. In patients with coronary artery disease, initial results show that carvedilol improved exercise capacity and left ventricular function and increased ejection fraction. There is also some evidence that left ventricular hypertrophy regresses in patients with hypertension treated with carvedilol and that the drug improves cardiac function in patients with idiopathic dilated cardiomyopathy. Pharmacokinetic Properties Carvedilol is rapidly absorbed when administered orally with maximum plasma concentrations (Cmax) reached 1 to 2 hours after single 25 or 50mg doses in healthy volunteers and hypertensive patients. Carvedilol undergoes extensive first-pass hepatic metabolism resulting in a low and variable absolute bioavailability of about 25%. The rate of absorption (as indicated by a slight increase in the time to reach maximum plasma concentrations), but not the extent of absorption, is decreased by food. Carvedilol is highly lipophilic and is widely distributed into extravascular tissues with a volume of distribution of 1.5 to 2 L/kg in healthy volunteers. Metabolism is primarily hepatic with less than 2% of a dose excreted unchanged in urine. Some metabolites appear to be active but whether this is of any clinical relevance is uncertain. Elimination is primarily biliary with 60% of a dose excreted in faeces. Thus, dosage adjustment in renally impaired patients is not required. However, peak plasma carvedilol concentrations and bioavailability are significantly increased in patients with severe hepatic impairment (e.g. cirrhosis) and the use of carvediîol in these patients is not recommended, Therapeutic Efficacy Data from clinical studies, analysed individually and combined in a meta-analysis, have conclusively demonstrated that carvedilol administered as a once daily 25mg dose has a significant antihypertensive effect in patients with mild-to-moderate essential hypertension. Indeed, a metaanalysis of 36 studies reported a decrease of 16/11mm Hg in mean systolic/diastolic blood pressures after 2 to 4 weeks of once daily (25mg) treatment in patients with a baseline blood pressure of 166/103mm Hg. No significant difference in antihypertensive effect was seen when carvedilol 50mg was administered daily as a single dose or as two 25mg doses. A 24-hour antihypertensive effect has been observed after once daily carvedilol administration in patients treated for 24 months. Published studies to date comparing the antihypertensive effect of carvedilol with that of other agents have generally enrolled small numbers of patients and may not have had sufficient statistical power to detect potential differences between treatments. Nonetheless, these studies have shown that in hypertensive patients (generally treated for 4 to 12 weeks) once daily carvedilol 25 or 50mg had a similar effect to that of once daily pindolol 15mg, atenolol 50 to l00mg, hydrochlorothiazide 25mg, or nitrendipine 2Omg (in elderly patients), or twice daily labetalol 2OOmg, propranolol 8Omg, metoprolol lOOmg, slow release nifedipine 20 to 4Omg or captopril 25 to 5Omg. In patients who had failed to respond sufficiently to hydrochlorothiazide therapy, the addition of carvedilol or atenolol produced a similar reduction in blood pressure after 6 weeks, with 67% of the carvedilol group and 71% of the atenolol group achieving a diastolic blood Carvedilol: A Review 235 pressure 90mm Hg. Other studies have demonstrated an additive antihypertensive effect when carvedilol 25mg and either hydrochlorothiazide 25mg, slow release nifedipine 2Omg, or nicardipine 60 mg/day were given in combination. In small groups of hypertensive patients with concomitant disorders, carvedilol reduced blood pressure in those with renal failure and in patients with non-insulin-dependent diabetes, carvedilol 25mg once daily was as effective as nifedipine lOmg 3 times daily. Compared with placebo, carvedilol increases exercise capacity and reduces myocardial oxygen consumption in patients with chronic stable angina pectoris and a 25mg dose administered twice daily has similar effects on total exercise time and time to 1mm ST-segment depression as slow release nifedipine 2Omg administered twice daily. In addition, initial studies show that carvedilol 12.5 to 5Omg twice daily has a beneficial effect (improved exercise time and resting left ventricular ejection fraction) in patients with chronic congestive heart failure (NYHA class II or III) secondary to ischaemic heart disease, although lower doses may be needed for safe initiation of therapy. Tolerability Results of a postmarketing surveillance study in 2226 patients treated with carvedilol for 12 weeks show that a daily 25mg dose administered as monotherapy is well tolerated by most patients. Treatment was withdrawn because of adverse events in 7% of patients; the most common adverse events responsible for withdrawal were vertigo (1.7%), headache (1.4%), bronchospasm (0.5%), fatigue (0.5%) and skin reactions (0.5%). Orthostatic hypotension has been reported in less than 1% of patients receiving carvedilol and has necessitated withdrawal of therapy in a few patients treated with a 5Omg daily dose. Dosage and Administration Most patients with mild-to-moderate hypertension respond to an oral carvedilol dose of 25mg administered once daily but if necessary this can be increased to 50 mg/day. All patients should initially receive 12.5mg daily for the first 2 days of therapy, and the maximum total daily dosage should not exceed 5Omg. The recommended dosage for elderly hypertensive patients is 12.5mg once daily; this can be titrated (at intervals of 2 weeks) up to a maximum of 50 mg/day. In clinical studies, most patients with stable angina pectoris or congestive heart failure received 12.5 to 50 mg twice daily. Carvedilol is not recommended for use in patients with hepatic dysfunction due to its increased bioavaiìability. Dosage adjustment is not necessary in patients with renal impairment. 1. Pharmacodynamic Properties Carvedilol (fig. 1) is an arylethanolamine ßadrenoceptor antagonist which appears to be weakly selective for ß1-adrenoceptors. The compound also has vasodilating properties, due primarily to 1adrenoceptor blockade. This dual pharmacological activity avoids many of the unwanted effects associated with agents that produce either vasodilation (e.g. reflex tachycardia) or -blockade (e.g. peripheral vasoconstriction). Carvedilol has no intrinsic sympathomimetic activity and weak membrane-stabilising ability (Abshagen 1987; Bristow et al. 1992; Sponer et al. 1987a). 1.1 Adrenoceptor-Blocking Activity 1.1.1 In Vitro and In Vivo Studies Carvedilol competitively antagonises ß1-adrenoceptormediated responses in several experimental models: isoprenaline (isoproterenol)-in-duced positive inotropic and chronotropic responses in isolated guinea-pig atria (Abshagen 1987; Hofferber et al. 1988; Kawada et al. 1990; Nichols et al. 1989a; Ruffolo et al. 1990a); isoprenaline-in-duced relaxation in dog coronary artery ring (Hat-tori et al. 1989); isoprenaline-induced tachycardia in pithed rats (Ruffolo et al. 1990a), and human cardiovascular tissues (myocardial sarcolemma, 236 Fig. 1. Structural formula of carvedilol; * the point of asymmetry. mammary artery, digital artery, metatarsai vein) [de Mey et al. 1992; Monopoli et al 1989; Moulds 1984]. The relative affinity of carvedilol for receptors can be evaluated based on its pA2 value (the negative decadic logarithm of the molar concentration of antagonist required to reduce the effect of agonist by 50%). Carvedilol demonstrated greater -adrenoceptor blocking activity than propranolol in isolated canine artery (pA2 values were 9.7 and 8.8, respectively) [Hattori et al. 1989] and was more potent (9.0) than labetalol (8.2), dilevalol (8.3) and brefanolol (7.8) in guinea-pig atria (Hofferber et al. 1988). In addition, the duration of ß1-adrenocep-tor-blocking activity in various conscious animals was greater with carvediíol (15 to 16 hours) than brefanolol (7.6 hours), labetalol (1.5 hours) or propranolol (12 hours) [Abshagen 1987; Hofferber et al. 1988; Sponer et al. I987a]. The following 2-adrenoceptor-mediated responses were antagonised by carvedilol: isoprenaìine-induced bronchodilation in isolated guinea-pig trachea (Abshagen 1987; Kawada et al. 1990; Nichols et al. 1989a; Ruffolo et al. 199Oa; Sponer et al. I987a), and salbutamol (albuterol)-induced vasodilation in pithed rats (Nichols et al. 1991; Ruffolo et al. 199Oa). In pithed rats, a dose of carvedilol giving a submaximal antihypertensive response in conscious spontaneously hypertensive rats produced 7-fold greater antagonism of ß1- than ß2- adrenoceptors, indicating weak selectivity for ß1- adrenoceptors (Nichols et al. 1991). In another study, carvedilol demonstrated higher affinity (between 6- and 39fold depending on the method used to assess receptor affmity) for ß1- than for 2- adrenoceptors Drugs 45 (2) 1993 in human ventricular myocardial tissue (taken from patients with end-stage heart failure) [Bristow et al. 1992a]. However, this result cannot be taken as an argument to use carvedilol in asthmatic patients. Carvedilol also antagonises 1-adrenoceptors in vitro and in vivo (Bristow et al. 1992b; Hofferber et al. 1988; Kawada et al. 1990; Mayer et al. 1988; Monopoli et al. 1989; Nichols et al. 1989a, 1991; Ruffolo et al. 199Oa; Seki et al. 1988; Sponer et al. 1987b). pA2 values ranged from 7.3 to 8.0 against the 1 -mediated contractile response to norepinephrine (noradrenaline) or phenylephrine in aortic strips compared with 6.5 for brefanolol or labetalol, 5.6 for dilevalol (Hofferber et al. 1988) and 8.3 for the specific 1- adrenoceptor antagonist, prazosin (Kawada et al. 1990). At equivalent ßadrenoceptor-blocking doses, carvedilol was 50% less active as an 1 -adrenoceptor antagonist than labetalol (Ruffolo et al. 199Oa), and between 2 and 50 times less active than prazosin depending on the tissue studied (Kawada et al. 1990). The ratio of 1: 1 blockade was greater for carvedilol (7.6: 1 for a 50 mg dose, 12.5 : 1 for a lOOmg dose) than for labetalol (4.9 : 1 for a 4OOmg dose) [Tomlinson et al. 1988]. In human myocardial tissue from undamaged hearts, the ß1: α1-receptor binding ratio was 1 : 2 for carvedilol compared with 1 : 77 for bucindolol, a direct-acting vasodilator (Bristow et al. 1992a). Carvedilol has an asymmetric centre giving rise to 2 enantiomers (fig. 1). In vitro investigations with the purified stereoisomers of carvedilol show that 1 -adrenoceptor blockade can be attributed primarily to the S(-)-enantiomer (Bartsch et al. 1990; Kuwahara & Misu 1989; Nichols et al. 1989b). In contrast, both enantiomers exhibit similar 1-adrenergic blocking activity (Bartsch et al. 1990; Nichols et al. 1989b). Thus, the maximum pharmacological effects of carvedilol can be achieved in the therapeutic dosage range only with the racemic mixture. At concentrations of l μmol/L, carvedilol noncompetitively inhibited the 2-adrenoceptormediated vasoconstrictor response to B-HT 920 in canine saphenous vein (Nichols et al. 1989a, 1991). As 2-adrenoceptor-mediated vasoconstriction in Carvedilol: A Review this model usually depends on the translocation of extracellular calcium, and since there is no conclusive evidence that carvedilol acts directly on 2adrenoceptors, it has been suggested that at concentrations of 1 μmol/L (which markedly exceeds that necessary for ß-adrenoceptor blockade) carvedilol may act as a calcium channel antagonist in vitro. Indeed, carvedilol antagonised the vasopressor response to a calcium channel activator in the pithed rat (Nichols et al. 1991) and relaxed potassium-depolarised rat uterus (Ruffolo et al. 199Oa). Further, carvedilol suppressed the contractile effects of potassium and BAY K8644, a calcium channel agonist, in canine coronary artery (Hattori et al. 1989). Calcium channel antagonists are highly effective vasodilators in cutaneous blood vessels (Rodeheffer et al. 1983; Smith & McKendry 1982) and, although of minor importance to its overall antihypertensive activity, calcium channel antagonism may be responsible for carvedilol-induced vasodilation observed in some local vascular beds. Indeed, in the rat acral cutaneous microvasculature (where vascular tone is not maintained by peripheral 1-adrenoceptors), carvedilol increased cutaneous perfusion by 64% and reduced cutaneous vascular resistance by 57% (Ruffolo et al. 199Ob). In contrast, at a dose producing a similar antihypertensive response, labetalol decreased cutaneous perfusion by 25% without significantly increasing cutaneous vascular resistance (Ruffolo et ai. 199Ob). 1.1.2 Human Studies The in vitro affinity of carvedilol for ß1, ß2~ and 1-adrenoceptors has been confirmed in human studies. Single intravenous doses of carvedilol (15mg) and labetalol (40 and 8Omg) antagonised ß1- and ß2-adrenôceptor-mediated effects of isoprenaline on blood pressure and heart rate in 24 healthy volunteers during 8 hours of testing (Cubeddu et al. 1987). The 1-mediated phenylephrine-induced pressor effect was also reduced. -Adrenergic blockade has also been demonstrated by inhibition of exercise-induced tachycardia in healthy volunteers (Tomlinson et al. 1987; 237 von Möllendorff et al. 19&6). Suppression of exercise-induced tachycardia peaked 45 minutes after oral administration of carvedilol 5Omg or metipranolol 5 or lOmg; the effect persisted for 10 hours following carvedilol administration, but was no longer evident 4.5 hours after administration of metipranolol. 1.2 Cardiovascular Effects 1.2.1 Blood Pressure and Heart Rate The effects of single oral doses of carvedilol on blood pressure and heart rate have been investigated in small numbers of healthy volunteers and in patients with essential hypertension (table I). In healthy volunteers, carvedilol 12.5 to 2OOmg reduced resting systolic and diastolic blood pressures with little or no associated reflex tachycardia and, when administered as a single dose, carvedilol 25mg, labetalol 2OOmg, propranolol 4Omg or pin-dolol lOmg were equally effective (table I). A single carvedilol dose of 25 or 5Omg significantly lowered resting systolic and diastolic blood pressures and heart rate in patients with essential hypertension (table I; fig. 2). Two hours after a single 12.5 to 25 (mean 23.6)mg dose, mean supine blood pressure was reduced from 160/97mm Hg to 138/86mm Hg (a decrease of 13/11%) in 18 resting hypertensive patients (Omvik & Lund-Johansen 1991). In exercising patients, mean blood pressure was reduced from 207/115mm Hg to 179/102mm Hg and was accompanied by a decrease of 12% in heart rate and an increase in stroke index resulting in a slight (6%) reduction in cardiac index (Omvik & Lund-Johansen 1991). In another study, maximal decreases in mean diastolic blood pressure of 15.5, 14.7, 22.5 and 9mm Hg occurred between 3 and 7 hours after the first dose of carvedilol 12.5, 25, 5Omg or placebo in 44 hypertensive patients (McPhillips et al. 1988). Using intra-arterial ambulatory blood pressure recording, Heber et al. (1987) recorded a significant reduction in systolic and diastolic blood pressure 30 minutes after a single 25mg dose of carvedilol in 12 hypertensive patients; a maximal reduction of 30/18mm Hg was reported after 90 minutes and 238 Drugs 45 (2) 1993 Table 1. Summary of some single dose haemodynamic studies of oral carvedilol (Car), placebo (PI) and other antihypertensive a gents in healthy volunteers and in patients with essential hypertension Reference No. of Dose (mg) subjects Maximum percentage change from baseline or placebo DBP SBP HR supine standing supine standing -34* -46* -38* -7* -2 -8* -50* -52* -44* -41 -52* -38 -5 -3 -4 -50* -56* -48* supine TPR standing Healthy volunteers Louis et al. (1987) 8a Sundberg et al. (1987) 13b Tomlinson et at. (1987) Car 25 Car 50 Lab 200 Car 50 Pin 10 Prop 80 PI Car 12.5 Car 25 Car 50 Car 100 Car 200 Prop 40 Prop 80 Prop 160 Prop 320 Pin 2.5 Pin 5 Pin 10 Pin 20 Lab 50 Lab 100 Lab 200 Lab 400 -5 -8 -8* -21* -17* -7 -7 -6 -8* -7 -12* -7 -12* -3 -8 -10 -9* -2 -5 -8 -19* -22* -2 NS -5 -3 -11 -16* -8 -9 -4 -7 -10 -12 -13* NS -21* -15* +9 +3 NS -2 +5 -10* -9 -12* -11* -1 -9* -8* -6 +6 +6 +7 +3 -18* -15* -14 NS NS -16 -16 +15 +13 Patients with essential hypertension Dupont et al. (1987) 10 10 Eggertsen et 10 al. (1984a) 10 Leonetti et al. 12 (1987) Omvik & 18 Lund18c Johansen (1991) Car 50 PI Car 25 Car 50 Prop 80 Car 50 Car 25d Car 25d -8** -11** -3 -8** -13**c -13** -14** -7** -16** -6** 9** -6** -10** -3 7** -11* -11** NS -6** -13** -4 -7** -10** -24** 9** -10C -8** -12** -11* -12** -25** -10 -15** -7 -6** a Elderly volunteers ( 60 years). b Results obtained 2h after drug administration. c Results from patients after exercising d Two patients (bodyweight < 70kg) received I2.5mg Abbreviations: SBP = systolic blood pressure; DBP = diastolic Wood pressure; HR =heart rate; TPR = total peripheral Lab = labetalol; Pin = pindoiol; Prop = propranolol; NS = not statistically significant; ** resistance; * p < 0.05 vs placebo or other **p < 0.05 vs baseline. active treatment; Carvedilol: A Review was maintained for the following 2 hours. A small but significant decrease in heart rate was seen 70 minutes after administration. During dynamic exercise (100W for men, 75W for women), carvedilol 5Omg significantly reduced the exercise-induced increase in systolic blood pressure and slightly (but nonsignifícantly) reduced the tachycardia response to exercise (Leonetti et al. 1987). In a study comparing the effects of single dose carvedilol 25mg and metoprolol lOOmg, both drugs reduced blood pressure significantly (p < 0.05) although this effect tended to be more pronounced with carvedilol 2 hours after administration (Morgan et al. 1987). Mean decreases in supine blood pressure were 17/1Omm Hg in the carvedilol group and 10/6mm Hg in the metoprolol group. Carvediiol had no significant effect on heart rate in this study, but metoprolol significantly (p 0.01) reduced supine and standing heart rate by 14 and 18 beats/min, respectively. Similarly, in another study carvedilol 25 or 5Omg reduced blood pressure significantly but had little effect on heart rate whereas a single propranolol 8Omg dose reduced supine and standing heart rate by about 25% and had little or no effect on blood pressure (Eggertsen et al. 1984a). Single oral doses of carvedilol 25mg and atenolol 5Omg, given in conjunction with diuretic therapy, produced similar reductions in supine and standing blood pressure in hypertensive patients with a supine diastolic blood pressure > 95mm Hg despite at least 4 weeks of prior therapy with bendroflumethiazide (bendrofluazide) 5mg daily (data on file, SmithKline Beecham Pharmaceuticals). A lower dose of carvedilol (12.5mg) had significantly less effect on supine and standing blood pressure and produced a significantly smaller reduction in blood pressure on standing than the 25mg dose. Carvedilol had a similar effect on blood pressure in elderly patients and their younger counterparts. In elderly hypertensive patients (aged 65 to 80 years, baseline supine blood pressure, 185/ 103mm Hg) mean peak supine blood pressure was reduced by 40/26mm Hg (vs 23/17mm Hg in patients aged < 50 years with a baseline supine blood pressure of 159/100mm Hg) after a single 239 Fig. 2. Mean systolic and diastolic blood pressure (SBP and DBF) in 18 hypertensive patients at rest or during exercise before and 2 hours after a single oral carvedilol 12.5 to 25mg dose (after Omvik & Lund-Johansen 1991). 12.5mg carvedilol dose and by 33/22mm Hg (vs 24/12mm Hg) after a 25mg dose (Morgan et al. 199Oa). The maximum antihypertensive response was seen after about 4 hours. Carvedilol 25mg and nitrendipine 2Omg daily had similar effects on supine blood pressure in elderly (aged > 60 years) hypertensive patients (Krönig et al. 1990). Systolic and diastolic blood pressures measured 2 hours after the first dose were reduced from 170/105 to about 165/102mm Hg in both treatment groups. 1.2.2 Peripheral Vascular Circulation The antihypertensive action of carvedilol is accompanied by a pronounced fall in total peripheral resistance in healthy volunteers; a decrease of about 34% was reported after a single 5Omg dose which remained evident 1 week later with continued dosing (Sundberg et al. 1987). Digital plethysmography revealed carvedilol-induced peripheral vasodilation following a threshold oral dose of 15mg with a linear increase in response (r = 0.78) up to 75mg (von Möllendorff et al. 1986). Vasodilation was observed 30 minutes after administration and persisted for up to 3 hours. A significant increase in arterial blood flow (maximum 156% of baseline) and a decrease in peripheral (forearm) resistance 24O (maximum 34%), which peaked after 4.5 hours and persisted for the entire 6-hour testing period, were observed in healthy volunteers after a single oral 75mg dose. Neither metipranolol 7mg nor carvedilol 5Omg affected venous capacity or tone (von Möllendorffetal. 1986). Other studies have confirmed a decrease in forearm arterial resistance following administration of carvedilol 5Omg in patients with essential hypertension (Cournot et al. 1992; Eggertsen et al. 1984b, 1987). Wrist occlusion negated the decrease in forearm vascular resistance in the study by Cournot et al. but the contribution of arteriolar dilation in the cutaneous circulation to the overall reduction in blood pressure remains unclear. No change in brachial artery diameter was noted despite a marked reduction in blood pressure, although brachial artery tangential tension decreased significantly (Cournot et al. 1992). Autoregulation of cerebral blood flow appears to be unchanged in hypertensive patients treated with carvedilol 25mg despite a marked reduction in mean arterial blood pressure (James et al. 1992; Kuriyama et al. 1990). Single intravenous infusions of carvedilol 5mg or propranolol 6mg had no significant effect on coronary arterial resistance or coronary blood flow related to rate-pressure product in patients with coronary artery disease, indicating that neither drug interfered with the adaptation of coronary flow to myocardial oxygen demand (Sievert et al. 1990). In spite of a marked reduction in renal perfusion pressure, renal blood flow was unchanged after single or multiple doses of carvedilol 5Omg (Dupont et al. 1990). As a consequence, renal vascular resistance was decreased and autoregulation of renal blood flow was preserved. A small but statistically significant decrease in glomerular filtration rate (8%) and filtration fraction (10%) occurred in hypertensive patients after a single 5Omg-dose; glomerular filtration rate was, however, preserved during 4 weeks of treatment with carvedilol (Dupont et al. 1987). Drugs 45 (2) 1993 1.2.3 Myocardial Function No significant changes in stroke index or cardiac index have been reported after single oral carvedilol 20, 4O, or 6Omg doses in healthy volunteers (Ajima et al. 1990). Mean cardiac index was reduced by 16% (p < 0.001) in sitting hypertensive patients 2 hours after a single 25 mg dose and by 6% (p < 0.05) in exercising patients. However, these reductions are markedly less that those associated with 'pure' 0adrenoceptor antagonists, particularly in exercising patients (Omvik & Lund-Johan-sen 1991). During long term administration, carvedilol 25 mg once daily for 6 to 9 months reduced cardiac index by 12% (supine), 17% (sitting) and 12% (after exercise) in hypertensive patients; after 1 year cardiac index was reduced by 5% (not significant) [Lund-Johansen & Omvik 1992]. In another study, a 50 mg daily dose reduced cardiac output by 20% after 4 weeks (p < 0.01 vs pretreatment value) without affecting left ventricular ejection fraction (Dupont et al. 1987). Intravenous carvedilol 15mg infused over 15 minutes had no effect on the duration of the PR, QRS or QT intervals, but a transient fall in T wave amplitude was noted in 2 subjects (Cubeddu et al. 1987). Several groups have investigated the effects of carvedilol on cardiac haemodynamics in patients with coronary artery disease (table II). Cardiac index was not significantly altered at rest or during exercise in patients treated with a single carvedilol 5Omg dose; in contrast, a single 4Omg dose of propranolol decreased cardiac index, particularly during exercise (13% reduction, p 0.005) [Wendt et aí. 1987]. Unlike propranolol which increased pulmonary capillary wedge pressure during exercise, carvedilol, by virtue of its vasodilating effects, decreased this parameter by 23% (p 0.005). In another study, diastolic function (as assessed by peak filling rate index and first-third filling fraction) improved during carvedilol administration dose dependently (Lahiri et al. 1987). After multiple doses of carvedilol in patients with angina (Lahiri et al. 1987) or hypertension (Heber et al. 1987), relative end-diastolic and end- Carvedilol: A Review 241 Table II. Summary of the effects of carvedilol (Car) on cardiac haemodynamic s and exercise capacity in patients with exerciseinduced angina pectoris Reference No. of patients Dose (mg) Maximum percentage change from baseline or placebo SBP rest DBF exer- rest cise HR exer- rest cise RPP exer- rest LVEF exer- cise cise -4 -8 -4 -8* -12 rest exercise Single-dose studies Freedman et al. (1987) 12 Kaski et al. (1985) 15 Wendt et al. (1987) 16 Car 25 Car 50 -2 -8 -4 -11* +2 -2 0 At 50 Car 25 -3 -16* a -6 _7*a <1 -1 -8 -16* -10* -5 Car 50 Prop 40 -11* +9 -3 -9 -7 +5 +1 +4 -8 -7 -4 -14* Car 25b Car 50b -5* -9* <1 -5 -2 -10* -2 -9* -17 -23* -10* -11* -4 -14* -11* -14* Multiple-dose study Lahiri et al. (1989) 6 +5 +20* +5 0 a Mean arterial blood pressure. b Carvedilol was administered daily for 2 weeks. Abbreviations: SBP = systolic blood pressure; DBP = diastolic blood pressure; HR = heart rate; RPP = rate pressure product; LVEF = left ventricular ejection fraction; At = atenolol; Prop = propranolol; statistically significant difference indicated by: * p 0.05 vs placebo. Absence of symbol indicates nonsignificant change or no p -value provided. systolic volumes and heart rate were reduced, again suggesting that carvedilol may decrease preload (i.e. cause venodilation) in addition to decreasing afterload. The decreased diastolic volume results in improved left ventricular function and ejection fraction in patients with chronic stable angina (Lahiri et al. 1987, 1989). The effects of carvedilol on cardiac haemodynamics in patients with idiopathic dilated cardiomyopathy have been investigated (Bristow et al. 1992b; Di Lenarda et al. 1991). Carvedilol 25 or 5Omg (duration of treatment not given) improved cardiac function, as assessed by resting left ventricular ejection fraction, and decreased cardiac, but not systemic adrenergic drive (Bristow et al. I992b). Carvedilol and metoprolol at the same dose (6.25mg) significantly reduced resting heart rate in patients with idiopathic dilated cardiomyopathy but only carvedilol significantly reduced mean pulmonary capillary wedge pressure and systemic vascular resistance while maintaining cardiac index (Di Lenarda et al. 1991). Regression of septal wall thickness (from 18.7 to 16.5mm) [Eichstäedt et al. 1992] and a 17% reduction in left ventricular mass index (Why & Richardson 1992) in patients with hypertension indicate that carvedilol induces regression in left ventricular hypertrophy in patients with hypertension. This would contribute to a decrease in myocardial ischaemia as a result of decreased myocardial work (and therefore oxygen demand). Thus, like other drugs with -adrenoceptor blocking properties, carvedilol appears to preserve myocardial function and may, therefore, have additional benefits in hypertensive patients with coronary artery disease. The effects of carvedilol on arrhythmias have been investigated in patients with hypertension (n=12), ischaemic heart disease (n=4l), and congestive heart failure (NYHA class II or III) secondary to ischaemic heart disease (n=12) treated for 4 to 8 weeks with carvedilol 25 to 100 mg daily (Senior et al. 1992). Overall, the number of premature ventricular contractions reported in 24 hours was reduced from 25 to 6 in 77% of patients, and an improvement in Lown's criteria was seen Drugs 45 (2) 1993 242 in 50% of all patients with the greatest improvement observed in patients with congestive heart failure (73% improved). 1.2.4 Cardioprotective and Neuroprotecüve Effects There is a substantial body of evidence supporting a cardiopfotective role for ß-adrenoceptor antagonists, in humans, these agents protect against ischaemia-induced myocardial injury, and in animal models of hypoxia and myocardial infarction, various parameters of damage, such as glycogen loss, increased pH of cardiac muscle and infarct size have been reduced by ß-blockers administered soon after coronary artery ligation. Depending on the animal model used, a 47 to 89% reduction in infarct size has been reported after treatment with intravenous carvedilol prior to occlusion (Bril et al. 1992; Feuerstein et al. 1992; Hamburger et al. 1991; Smith et al. I992a,b; Valocik et al. 1991). Propranolol and celiprolol, administered at comparable ß-blocking dosages, had little or no effect on infarct size in these animal models (Feuerstein et al. 1992). In addition, carvedilol administered before coronary artery occlusion reduced the extent of myocardial ischaemia/reperfusion injury and significantly improved survival in a permanent coronary artery occlusion model of myocardial infarction (Ruffolo et al. 1992; Smith et al. 1992). In rats it has been shown that the loss of glycogen in myocardial tissue as a consequence of hypoxic stress was protected to a considerably greater extent by carvedilol than by comparable ß-blocking doses of propranolol (Bartsch et al. 1988). The mechanism underlying the cardioprotective action of carvedilol is not known; however, the enhanced cardioprotective effects of carvedilol over propranolol at similar ß-blocking doses may suggest that carvedilol possesses additional cardioprotective effects which are unrelated to ß-adrenoceptor blockade. Recent studies have shown that carvedilol inhibits oxygen free radical-initiated lipid peroxidation in rat brain tissue and it was an order of magnitude more potent than other ß-blockers in this regard (Yue et al. I992a). Further, carvedilol prevented macrophage- and Cu2+- induced human low density lipoprotein oxidation (a contributing factor in the progress of atherosclerosis) in vitro via free radical scavenging (Yue et al. 1992b). Although the clinical relevance of these findings remains to be determined, it is possible that these properties may provide the additional cardioprotection that has been observed with carvedilol in animal models of acute myocardial infarction (Ruffolo et al. 1992). Free radical generation mediates part of the ischaemic neuronal damage caused by excitatory amino acids such as glutamate. As carvedilol has been shown to scavenge free radicals in in vitro models, its neuroprotective activity in in vitro and in vivo models of brain ischaemia has been investigated (Lysko et al. 1992). Carvedilol protected cultured cerebellar granule cell neurons against glutamate-mediated toxicity [concentration producing 50% protection (ICso) 1.1 μmol/L] and inhibited lipid peroxidation (ICso. 5 μmol/L). More importantly, in gerbils pretreated with carvedilol 3 mg/kg for 6 days before being exposed to global brain ischaemia and reperfusion, carvedilol-treated animals had an increased number of viable neurons compared with untreated control animals (Lysko etal. 1992). 1.3 Other Effects Proliferation of vascular smooth muscle cells in response to mitogenic stimuli derived from macrophages, endothelial cells and platelets is a major factor contributing to the development of atherosclerosis. Carvedilol produced a concentration dependent decrease in basal and endothelin-1 induced [3H]thymidine incorporation in rat aortic vascular smooth muscle cells over the range 0.1 to 10 μmol/L (IC50 1 μmol/L) and reduced the mítogenic response to a variety of potent smooth muscle rnitogens (such as angiotensin II, thrombin, epidermal growth factor, and platelet-derived growth factor) [Sung et al. 1992]. These effects were reversible and were not demonstrated by other ßadrenoceptors at a similar concentration level. Further studies are needed to explain the mechanisms underlying the antiproliferative effects of Carvedilol: A Review carvedilol, and to demonstrate the clinical importance of such effects. Reflex stimulation of the renin-angiotensin-aldosterone system occurring in response to a decrease in total peripheral resistance induced by pure vasodilators may lead to fluid retention and negation of the antihypertensive effect of these drugs. This reflex effect is suppressed via antagonism of ß-adrenoceptor blockers; plasma renin activity and aldosterone levels are therefore unchanged or decreased by single or multiple doses of carvedilol (Dupont 1990; Dupont et al. 1990; Leonetti et al. 1987; Morgan et al. 1987). Fluid retention (as assessed by changes in bodyweight or urinary sodium retention) has not been observed in patients treated with carvedilol (Dupont et al. 1987, 1990; Omvik et al. 1992), and blood urea nitrogen and serum creatinine have remained unchanged (Tomita et al. 1991). In addition, levels of atrial natriuretic peptide were reduced by 27% at rest (supine) in hypertensive patients after the first dose of carvedilol, probably as a counter-regulatory response to the reduction in cardiac index, but no further response was seen during long term treatment or during exercise (Omvik et al. 1992). As a result of its ability to antagonise 2-adrenoceptors (section 1.1.1), carvedilol may be expected to induce clinical effects resulting from this action. While the effects of carvedilol in asthmatic patients have not been reported, single oral doses of 25 or 5Omg had no statistically significant effects on pulmonary function [forced vital capacity (FVC), forced expiratory volume in 1 second (FEV1), FEV1/FVC, peak expiratory flow rate (PEFR), and maximum expiratory flow at 50% (MEFso) and 25% (MEF25) of vital capacity] in healthy volunteers (Sundberg et al. 1987; Tiedemann & Peters 1984). No clinically significant adverse effects have been reported on serum cholesterol, triglyceride, high or low density lipoprotein-cholesterol, or apolipoprotein levels in normotensive or hypertensive subjects in clinical trials (Ehmer et al. 1988; Goto etal. l99l;Schnurretal. 1987; Seguchi et al. 1990). These findings have been confirmed in a meta-analysis of 36 studies in which patients received car- 243 vedilol for a median of 8 to 12 weeks (Stienen & Meyer-Sabellek 1992). However, in a subgroup of patients with triglyceride levels >3.9 mmol/L, carvedilol reduced triglyceride levels by 1.4 mmol/L (Seguchi et al. 1990). In a more recent study, carvedilol 25 to 50 mg/day (n = 116) and captopril 25 to 50 mg/day (n = 117) had similar favourable effects on serum lipids in hypertensive patients with WHO stage I or II dyslipidaemia [high density lipoprotein (HDL)- cholesterol <l.O mmol/L]. HDL-cholesterol levels increased by about 10%, total cholesterol levels decreased by about 10% and triglyceride levels decreased by about 14% with both drugs (Hauf-Zachariou et al. 1992). Although some -blockers may produce adverse metabolic effects in patients with diabetes, carvedilol appears to have no effect on glucose homeostasis in hypertensive patients with non-insulindependent diabetes (Albergati et al. 1992; Ehmer et al. 1988). Neither carvedilol nor nifedipine significantly affected glucose metabolism as assessed by the intravenous glucose tolerance test after 4 weeks of drug treatment (Albergati et al. 1992). Another study showed that after 8 weeks of twice daily administration of carvedilol 25 to 5Omg in 89 patients with non-insulin-dependent diabetes, fasting and postprandial blood glucose levels were maintained within a narrow range, glycosylated haemoglobin levels (an indication of long term blood glucose control) were unchanged, and no hypoglycaemic episodes were reported (Ehmer et al. 1988). There have been no published reports of the effects of carvedilol in patients with insulindependent diabetes, although unpublished data (SmithKline Beecham) indicate that the drug provides similar efficacy and tolerability, without affecting blood glucose, in these individuals. 1.4 Mechanisms of Action The data summarised in previous sections indicate that carvedilol reduces systolic and diastolic blood pressure acutely primarily by decreasing total peripheral resistance. Cardiac function is generally preserved and heart rate is either unchanged or decreased slightly. Drugs 45 (2) 1993 244 Carvedilol is a ß-adrenoceptor antagonist which exerts its vasodilating activity primarily via antagonism of peripheral 1-adrenoceptors. At concentrations higher than those needed to antagonise ß-adrenoceptors, carvedilol may act as a calcium channel blocker. This activity may be important in regional vascular beds, such as the cutaneous circulation, where carvedilol (unlike other vasodilators and ß-adrenoceptor antagonists) has a potent vasodilator effect (see section 1.2.2). Several lines of evidence suggest that mechanisms other than 1 -blockade are involved in the vasodilatory effects of carvedilol (Sponer et al. 1987b). Indeed, Belz et al. (1988) have shown that carvedilol 5Omg not only attenuated the vasoconstrictive effect of noradrenaline (norepinephrine) on human hand veins, but also decreased the effect of prostaglandin F2, a nonadrenergic vasoconstrictor. In addition, the relatively weak occupancy of α-adrenoceptors by carvedilol cannot fully explain the effective inhibition of prostaglandin P2induced vasoconstriction in human hand veins in vivo when compared with the α-blocker, prazosin, again indicating another mechanism of vasodilation (Beermann et al. 1992). The mechanisms underlying the cardioprotective effects of carvedilol have not been fully established but it seems clear that the antioxidant and antiproliferative effects demonstrated in vitro may be contributing factors. Although further studies are needed to confirm the findings of in vitro and in vivo studies in the clinical setting, there is no doubt that the -blockade and vasodilation, along with the reduction in oxygen consumption, play a considerable role in the cardioprotective effects demonstrated in different experimental models. 2. Pharmacokinetic Properties The pharmacokinetic properties of carvedilol have been investigated in healthy volunteers and in patients with hypertension or angina pectoris. The influence of age and renal or hematic disease on the disposition of carvedilol has been reported. Carvedilol concentrations in plasma or serum and urine have been measured using high perform- ance liquid chromatography (HPLC) with spectrofluorometric detection which has a lower limit of detection of 0.38 to 5 μg/L in plasma or serum and 0.82 μg/L in urine (Louis et al. 1987; Neugebauer et al. 1990; Powell et al. 1987; Reiff 1987; Varin et al. 1986). 2.1 Absorption and Distribution Carvedilol is rapidly absorbed after a single oral dose with maximum plasma concentrations (Cmax) achieved within 1 to 2 hours (tmax) in healthy volunteers and hypertensive patients (table III). Peak plasma concentrations of carvedilol increased linearly with dose and absorption was not altered after repeated doses (McPhillips et al. 1988; Morgan et al. 199Ob; table III). Furthermore, there was no accumulation of carvedilol during multiple dose administration, as indicated by similar mean area under the plasma concentration-time curve (AUC) values compared with single dose administration (McPhillips et al. 1988). Although the rate of absorption was decreased slightly when carvedilol was taken with food (tmax increased from 0.97 to l.3h), the extent of absorption was unaffected, as shown by unchanged AUC and Cmax values (Louis et al. 1987; table III). After oral administration carvedilol undergoes extensive first-pass hepatic metabolism which results in a relatively low and variable absolute bioavailability of about 25% (von Möllendorff et al. 1987). Carvedilol is available as a racemic mixture of its R(+)- and S(-)-enantiomers and stereoselective differences in pharmacokinetics have been reported (Neugebauer et al. 1990). In healthy volunteers, mean AUC values for the S(-)-enantiomer were lower than those for the R(+)-enantiomer after intravenous and oral administration of racemic carvedilol. The difference was greatest after oral administration with the enantiomeric ratio (R: S) ranging from 1.6 to 4.4 (median 2.7). The mean maximum plasma concentraion of R(+)-carvedilol was 2.6-fold greater than that of S(-)-carvedilol and absolute oral bioavailability was 31% for the R(+)- Carvedilol: A Review 245 Table I. Mean or median pharmacokinetic values reported after single (sd) or multiple oral doses of carvedilol Reference Healthy volunteers Louis et al. (1987) von Möllendorff et al. (1987) Hypertensive patients McPhillips et al. (1988) Morgan et al. (1990b) No. of subjects 4a 4a 6a 18 19 44 8 21C Rudorf & Ehmer (1988) 12 Carvedilol dose (mg) Duration Pharmacokinetic parameters Cmax (μg/L) tmax (h) AUC (μg/L·h) t1/2 (h) 25 50 50 + food 25 50 50b sd sd sd sd sd sd 67 122 128 0.97 0.97 1.3 337 717 741 21 66 1.47 1.2 157 348 128 0.66 327 4.3 12.5 25 50 I2.5od 25od 5Ood I2.5od 25od 5Ood I2.5od 25od 5Ood 25 25 + HCTZ 25 sd sd sd 4w 4w 4w 2w 2w 2w 2w 2w 2w sd sd 39 75 161 32 75 161 58 1.3 180 410 1097 184 343 1136 225 6.5 7.9 7.0 8.3 7.8 7.6 2.3 105 189 69 151 252 72 1.3 1.75 0.9 1.0 1.3 1.8 572 208 947 1600 272 4.3 5.0 1.9 4.7 5.3 5.8 1.5 276 6.6 60 1.8 1.8 2.2 7.06 6.35 a Volunteers aged 53 to 65 (mean 61) years. b Administered as an oral suspension. c Patients aged > 65 years. Abbreviations: Cmax = maximum plasma carvedilol concentration; t max = time to achieve maximum plasma concentration; AUC = area under the plasma concentration-time curve; t½ = terminal elimination half-life; HCTZ = hydrochlorothiazide; od = once daily; w = weeks. enantiomer and 15% for the S(-)-enantiomer in healthy volunteers indicating marked stereoselectivity in first-pass hepatic metabolism (Neugebauer et al. 1990). Carvedilol is a highly lipophilic compound which is extensively distributed into extravascular tissues following absorption (Varin et al. 1986). The volume of distribution is about 1.5 to 2 L/kg in healthy volunteeers (Cubeddu et al. 1987; Varin et al. 1986; von Möllendorff et al. 1987). Carvedilol is highly bound to plasma proteins ( 95%) [von Möllendorff et al. 1987]. Binding appears to be lower for the S(-)- enantiomer than for the R(+)enantiomer (Fujimaki et al. 199Oa) and is un- changed in patients with hepatic disease (Neugebauer et al. 1988). 2.2 Metabolism and Elimination Carvedilol is rapidly and extensively metabolised with less than 2% of a dose recovered as unchanged drug in urine (Neugebauer et al. 1987; Neugebauer & Neubert 1991). Clearance is almost exclusively via hepatic metabolism with the major metabolites being the glucuronide conjugate, aliphatic side-chain oxidative products and aromatic ring hydroxylated conjugates; some of these appear to be pharmacologically active although the clinical Drugs 45 (2) 1993 246 relevance of this has not been established (Neugebauer & Neubert 1991). About 60% of the metabolites are excreted into bile and are eliminated in faeces with urinary recovery accounting for 16% of metabolites (Neugebauer et al. 1987). In hypertensive patients, the terminal phase elimination half-life of carvedilol after oral administration ranges from about 2 to 8 hours and was about 2 to 5 hours in elderly (aged > 65 years) hypertensive patients (table III). Three-compartmental analysis revealed a prolonged apparent terminal elimination half-life of up to 14.5 hours after intravenous administration (Powell et al. 1987). 2.3 Effects of Age and Disease States Since carvedilol undergoes extensive first-pass hepatic metabolism, it is reasonable to expect that its pharmacokinetic profile would be altered in patients with hepatic impairment. Compared with healthy volunteers, patients with cirrhosis showed a 36% decrease (36.5 vs 23.3 L/h) in plasma clearance and a 280% increase in steady-state volume of distribution (125 vs 321 L/h; Neugebauer et al. 1988). In these patients, a significant increase in Cmax (104.3 vs 23.7 μg/L) and bioavailability (82.6 V5 18.6%) was observed compared with healthy volunteers but elimination half-life was unaltered (Neugebauer et al. 1988). As carvedilol is eliminated primarily in faeces, renal impairment would not be expected to necessitate dosage adjustment. Indeed, in hypertensive patients with chronic renal failure, peak plasma concentrations and elimination half-life of carvedilol were not significantly altered compared with values obtained in healthy volunteers (Hakusui & Fujimaki 1988; Kramer et al. 1992). In addition, the pharmacokinetics of carvedilol were not altered in hypertensive patients with severe chronic renal failure who were undergoing dialysis (Miki et al. 1991). The pharmacokinetics of single doses of carvedilol were not significantly changed in elderly hypertensive patients (aged 64 to 79 years) compared with their younger counterparts (Morgan et al. 199Ob), with a tendency towards increased peak plasma concentrations and AUC values in elderly patients. 3. Therapeutic Efficacy The therapeutic efficacy of carvedilol has been investigated in patients with essential hypertension, mainly of mild-to-moderate severity. Several studies have compared the efficacy of carvedilol with that of other antihypertensive agents and its use in combination therapy with a diuretic or calcium antagonist has also been reported. Most of these clinical trials involved small numbers of patients and may not have had sufficient statistical power to permit fair conclusions regarding the differences between treatments. Carvedilol has demonstrated antianginal activity in patients with chronic stable angina pectoris and there are preliminary clinical data indicating its potential in the treatment of patients with congestive heart failure (NYHA class II or III) secondary to coronary heart disease. 3.1 Mild-to-Moderate Essential Hypertension 3. 1.1 Noncomparative Studies, Dose Response Studies and Comparisons with Placebo Several studies have shown that a daily dose of carvedilol 25 or 5Omg significantly reduces systolic and diastolic blood pressure in patients with mild-to-moderate hypertension at rest or during exercise (Eggertsen et al. 1984b, 1987; Heber et al. 1987; Leonetti et al. 1987; LundJohansen et al. 1992; Meyer-Sabellek et al. 1987; Morgan et al. 1987; Schnurr et al. 1987). A diastolic blood pressure of <9Omm Hg was achieved in 85% (73 of 86) eva-luable patients (pretreatment diastolic blood pressure 95 to 115mm Hg) treated for 12 months with carvedilol 25 mg twice daily in a noncomparative study with 9 patients requiring dosage adjustment (50 mg twice daily or 25 mg once daily; Schnurr et al. 1987). In a meta-analysis of 36 clinical studies which enrolled 3412 hypertensive patients, carvedilol 25mg administered once daily reduced mean systolic and diastolic blood pressures (measured the morning before drug administration) by 16/11mm Carvedilol: A Review Hg compared with baseline (166/103mm Hg); there was no clinically significant advantage observed in patients who received a single 50 mg dose (mean change from baseline 18/13mm Hg) or 25mg twice daily (mean change from baseline 15/1Omm Hg) [Stienen & Meyer-Sabellek 1992]. A noncomparative study which used intra-arterial ambulatory recording to measure blood pressure has shown that after 4 weeks of treatment with carvedilol 25 or 50 mg/day systolic and diastolic blood pressures were reduced, and that this reduction was maintained over 24 hours (Heber et al. 1987). Mean daytime reductions in systolic and diastolic blood pressures were 25 and 19mm Hg, respectively, in 12 hypertensive patients; at night-time mean blood pressures decreased by 13 and 8mm Hg, respectively. Blood pressure was reduced by 26/16mm Hg at peak isometric exercise. When compared with placebo over a 4-week treatment period, carvedilol 12.5, 25 and 50 mg daily reduced blood pressure within 2 hours of administration and maintained supine diastolic blood pressure below baseline levels for 24 hours (McPhillips et al. 1988; Meyer-Sabellek et al. 1987, 1988). Trough supine diastolic blood pressures after 4 weeks of treatment were 0.6, 7.3, 8.8 and 12.1mm Hg below baseline in patients who received placebo, or carvedilol 12.5, 25 and 5Omg daily, respectively (McPhillips et al. 1988). Daily carvedilol doses as low as 5mg have been effective in Japanese patients, who generally require lower therapeutic dosages than Caucasian patients (Ogihara et al. 1987, 1988). A significant antihypertensive effect (p < 0.05 vs placebo) was demonstrated in 15 patients with mild-to-moderate hypertension who were treated with carvedilol 25 or 5Omg twice daily for 12 months followed by 12 months of once daily treatment (50 or lOOmg) [Meyer-Sabellek et al. 1988]. Ambulatory blood pressure monitoring revealed a persistent 24-hour reduction in systolic and diastolic blood pressure after 6 and 12 months on a once daily regimen; mean daily doses after 24 months were 5Omg in 20% of patients and lOOmg in 80% of patients. 247 3.1.2 Comparisons with Other Antihypertensive Agents Table IV summarises the results of several studies in which carvedilol has been compared with other antihypertensive agents. In these studies, carvedilol 25mg once daily (in some studies 5Omg once daily was administered) had a similar efficacy to twice daily administration of labetalol 2OOmg, metoprolol lOOmg or captopril 25 to 5Omg, and to once daily administration of pindolol 15mg, hydrochlorothiazide 25mg or nitrendipine 2Omg in elderly hypertensive patients. Carvedilol 25mg once daily, atenolol 5Omg once daily, and slow release nifedipine 2Omg twice daily were compared in 293 hypertensive patients (Hall et al. 1991). Patients were randomised to receive therapy for 12 weeks; however, if an inadequate response was observed after 4 weeks, the daily drug dose could be doubled. Blood pressure (measured 1 hour postdose) was reduced in all treatment groups [by at least 20mm Hg (systolic) and 10mm Hg (diastolic)] with no significant differences observed between treatment groups. Doubling of the dose was necessary in 30% of carvedilol recipients (n = 29), in 24% of atenolol recipients (n = 23) and in 27% of nifedipine recipients (n = 25). The effects of carvedilol 25 to 50 mg/day and captopril 25 to 50 mg/day have been compared in 283 evaluable hypertensive patients in a multicentre study (data on file, SmithKline Beecham). After 8 weeks there was no marked difference in response between the treatment groups with 79% of carvedilol recipients and 70% of captopril recipients achieving a mean sitting diastolic blood pressure of 9Omm Hg and/or reduction in diastolic blood pressure from baseline lOmm Hg according to intention-to-treat analysis. Further analysis revealed a greater response in elderly hypertensive patients (aged 65 years) and in patients with a baseline diastolic blood pressure of 95 to 105mm Hg who were treated with carvedilol compared with those who received captopril. About 45% of patients in each treatment group had failed to respond (mean sitting diastolic blood pressure 90 mm H g o r a r ed uc ti o n fro m b as el i ne 1 0 mmHg) after 2 weeks and required an in- 248 Drugs 45 (2) 1993 Table IV. Double-blind studies comparing carvedilol (Car) with other antihypertensive drugs when administered with or without concomitant diuretic therapy in patients with mild-to-moderate essential hypertension Reference No. of patients Dosage (mg) Duration of treatment (weeks) Percentage reduction compared with placebo or pretreatment values systolic/diastolic BP supine standing HR supine Patient response rate (%)a standing ß-Blockers Eggertsen et al. (1984b) Lambert et al. (1991) Morgan et al. (1987) Ollivier et al. (1990) Rittinghausen (1988) Young et al. (1992) 10 10 10 16 17 14 30 31 39 40 38 35 Car 25 bid Car 50 bid Prop 80 bid Car 25 od Lab 200 bid Car 50 od Met 100 bid Car 25 od Lab 200 bid Car 25 od Car 50 od Car 100 od Pin 15 od 47 52 Car 25-50 od At 50-1 00 od 4 4 4 8 13 8*/7* 9*/8* 9*/9* 6» 6b 13*/13* 16*/11* 14*/18* 16*/18* c/14 9*/7* 876* 12*/10* 4b 6b 13*/16* 10*/13* 10* 19* 20* 14 9 16* 10* 14* 15* 15* 19* 19* 19* 17* 87 87 84 c /15 84 100 84 84 91 c/18 8 8 c/16 Nitrendipine (Nit) Kronig et al. (1990) 33d 31d Car 25 od Nit 20 od 12 Car 25-50 od Cap 25-50 bid 8 Captopril (Cap) Data on file, SmithKline Beecham 141 142 17*θ Compared with, and use in combination with, hydrochloroth¡az¡de (HCTZ) Dupont et. al. (1990) Langdon et al. (1991) van der Does et al. (1990) Widman et al. (1990) 15 87 92 54 58 59 Car 25-50 od + HCTZ 25 od Car 25-50 ode HCTZ 25-50 ode Car 25 od + HCTZ 25 od At 50 od l· HCTZ 25 od C 25 od + HCTZ 25 od At 50 od + HCTZ 25 od 1.5 3* NS 22*/19* 29*/2O* 11/10 79 78 79 70 16*β13*e 7*9 19 12/9 38 53 86 88 67 8{5f 10*9 8*9 9/1 1f 9/1 Of 71 39 50 1Γ/14*9 17169 11716*9 9*9 7*/9h a Diastolic blood pressure 90 mm Hg except in the study by Kronig et al. (1990) where < 95mm Hg was used, b Change in mean 24-hour ambulatory blood pressure values, c No values for systolic blood pressure provided, d Patients aged 60 years. e Dosage was doubted to Car 50 mg/day and HCTZ 50 mg/day in 32% of carvedi!ol recipients and in 30% of HCTZ recipients in whom mean sitting diastolic blood pressure was > 90mm Hg or had not decreased by 10mm Hg since baseline assessment, f Measurements taken in the sitting position. „. g Percentage change from values recorded after 4 weeks of hydrochtorothiazide monotherapy. h Percentage change from values recorded after 4 weeks of carvedilol or atenolσl monotherapy. Abbreviations and symbols: At = atenolol; bid = twice daily; BP = blood pressure; HR = heart rate; Lab = labetalol; Met = metoprolol; Pin - pindolol; Prop - propranolol; od = once daily; * p 0.05 versus placebo or pretreatment values. Carvedilol: A Review creased dosage. After a further 6 weeks of therapy at the higher dosage level, 46% of the remaining carvedilol recipients and 43% of the captopril recipients had achieved a normalised sitting diastolic blood pressure ( 90mm Hg). Carvedilol 25mg and nitrendipine 2Omg, both administered once daily, had(similar antihypertensive effects in elderly hypertensive patients (aged 60 years, mean baseline blood pressure 170/ 105mm Hg) [fig. 3]. After 12 weeks of treatment, supine blood pressure was reduced by 22/19mm Hg in the carvedilol group and by 29/20mm Hg in the nitrendipine group. Almost 80% of patients in each group achieved a diastolic blood pressure 95mm Hg after 12 weeks of therapy (Krönig et al. 1990). 3.1.3 Use in Combination with Other Antihypertensive Agents In hypertensive patients who had failed to respond to 4 weeks of hydrochlorothiazide therapy, the addition of carvedilol produced a marked reduction in blood pressure; in 1 study, 67% of patients who received carvedilol 25mg once daily and 71% of patients who received atenolol 5Omg once daily in combination with hydrochlorothiazide 25 mg/day achieved a mean diastolic blood pressure 9Omm Hg after 6 weeks (van der Does et al. 1990; table IV). Mean sitting blood pressure (measured 24 hours after drug administration) was reduced from 158/101mm Hg after 4 weeks of hydrochlorothiazide monotherapy (25 mg/day) to 140/90mm Hg after 2 days of concomitant carvedilol I2.5mg once daily (a decrease of 18/11mm Hg) [Dupont et al. 1990]. No further reduction in blood pressure was seen after increasing the carvedilol dosage to 25mg once daily for an additional 7 days. Two other studies have investigated the efficacy of combined therapy with carvedilol (5 to 2Omg daily) and a thiazide diuretic in Japanese hypertensive patients (Ogihara et al. 1991; Yasujima et al. 1988). In patients with moderate-to-severe hypertension (diastolic blood pressure >110mm Hg after 1 to 2 weeks of diuretic therapy), about 80% of patients had responded (diastolic blood pressure < 100mm Hg or had decreased by lOmm Hg) after 249 12 weeks of combination therapy (Ogihara et al. 1991). A similar response rate (74%) was seen after 8 weeks of combined therapy in patients with mildto-moderate hypertension (Yasujima et al. 1988). In both studies a dose dependent increase in response rate was observed over the administered dosage range (5 to 2Omg once daily). Data obtained from 14 hypertensive patients (mean supine diastolic blood pressure 100 to 115mm Hg) show that combined treatment with carvedilol 25mg once daily and slow release nifedipine 2Omg twice daily has an additive antihypertensive effect (Juttmann et al. 1992). Mean peak Fig. 3, Mean supine systolic and diastolic blood pressures and heart rate in elderly patients with mild-to-moderate essential hypertension before and at trough after 4 and 12 weeks' treatment with carvedilol 25 mg/day (n = 33) or nitrendipine 20 mg/day (n = 32) [after Krönig et al. 1990]; * p < 0.05 compared with pretreatment values. 250 reductions in supine blood pressure after 1 week were 21/ 11 mm Hg with carvedilol monotherapy, 20/16mm Hg with nifedipine monotherapy, and ranged from 26 to 40mm Hg (systolic) and 14 to 23mm Hg (diastolic) after 1, 3 and 10 days of combined treatment. Mean trough blood pressure (measured prior to the morning dose) did not decrease significantly with either drug given as monotherapy or during combined treatment possibly because the duration of treatment in this study did not allow the full development of antihypertensive effects. An earlier study showed similar results in Japanese hypertensive patients who had not responded to 4 weeks of nicardipine 60 mg/day therapy (mean sitting blood pressure 171/ 101mm Hg) [Takabatake et al. 1988], Mean blood pressure was 156/91 mm Hg (a decrease of 15/ 1Omm Hg after 2 weeks of combined therapy with nicardipine 60 mg/day and carvedilol (mean daily dose 8.9 mg) and was 141/85mm Hg after 12 weeks (a decrease of 30/16mm Hg). 3.1.4 Use in Special Patient Groups The efficacy of carvedilol has been investigated in 9 Japanese hypertensive patients with renal failure. Systolic/diastolíc blood pressure was lowered from 172/101 to 150/87mm Hg after 2 to 4 weeks of therapy with carvedilol 5 to 20 mg/day (Kohno et al. 1988). In another study, 12 of 23 hypertensive Japanese patients with renal failure (serum creatinine level 2 mg/100ml) achieved a blood pressure of 150/90mm Hg or a decrease of mean arterial blood pressure of 13mm Hg after 8 weeks of carvedilol monotherapy; 74% of patients (14 of 19) receiving carvedilol plus a diuretic achieved a similar response (Takeda et al. 1990). Carvedilol 25mg twice daily was more effective at reducing blood pressure than metoprolol 5Omg twice daily in hypertensive patients with non-insulin-dependent diabetes (Ehmer et al. 1988). After 4 weeks, 23 of the 25 patients (92%) treated with carvedilol showed a good response to therapy (defined as a reduction of diastolic blood pressure to <9Omm Hg) compared with 79% of patients in the metoprolol group. After a further 4 weeks of therapy Drugs 45 (2) 1993 in which doses were doubled in nonresponding patients, response rates were unchanged in the carvedilol group but increased to 83% in the metoprolol group. In another study, carvedilol 25mg once daily was as effective as nifedipine lOmg administered 3 times daily in 20 patients with noninsulin-dependent diabetes; after 4 weeks mean sitting systolic/diastolic blood pressure was reduced by 24/7mm Hg in the carvedilol group and by 2O/ 8mm Hg in the metoprolol group with no significant difference between the groups (Albergati et al. 1992). No changes in glucose metabolism (as assessed by intravenous glucose tolerance testing), levels of glycosylated haemoglobin, the number of hypoglycaemic episodes or the use of oral hypoglycaemic medication were observed during these studies (see section 1.3). 3.2 Chronic Stable Angina Pectoris The use of conventional ß-adrenergic blocking agents in the treatment of angina pectoris is well established. However, in patients with left ventricular dysfunction ß-blockade may produce adverse haemodynamic consequences such as increased peripheral and coronary resistance, and decreased cardiac output. Thus, drugs such as carvedilol, which produce -blockade and vasodilation, would be expected to offer the benefits of ß-blockade (i.e. decreased myocardial workload) without the attendant unwanted effects of myocardial and peripheral vasoeonstriction (Kelly & Freedman 1989). Carvedilol 25 or 5Omg twice daily has been compared with placebo in patients with a history of stable exercise-induced angina for at least 3 months (Rodrigues et al. 1986). Within 2 weeks, carvedilol 25mg twice daily produced clinically and statistically significant increases in exercise performance and tolerance as indicated by increased time to 1mm ST-segment depression, reduced myocardial oxygen consumption [rate-pressure product (RPP)] during exercise, and increased total exercise time (table V). 24-Hour ambulatory electrocardiographic monitoring indicated reductions in the total number of episodes of ST-segment depression of 57% (carvedilol 25mg) and 47% Carvedilol: A Review 251 Table V. Summary of some studies comparing carvedilol (Car) with placebo or nifedipine (Nif) in patients with chronic stable angina pectoris Reference No. of Study Study Dosage patients design duration (mg bid) (weeks) Percentage change from placebo total time to 1mm rate-pressure ST-segment depression product at peak exercise exercise time ** Placebo Lahiri et al. (1987) Rodrigues et al. 18 17 sb sb 2 Car 25 2 Car 50 Car 25 +22 +16* -19 -16 Car 50 +24 +32* -24 Car 25 Nif 20 SR +34* +22* +41* +29* -13* -8* (1986) -12 Nifedipine van der Does eí al. (1991) 74 69 db, pg 4 Abbreviations and symbols: bid = twice daily; db = double-blind; pg = parallel groups; sb = single-blind; SR = slow release. Statistically significant difference compared with placebo: * p < 0.05 level. (5Omg) while painful episodes of angina were reduced by 92% and 62%, respectively (Rodrigues et al. 1986). Despite the increased workload achieved, peak exercise ST-segment depression was not altered. Doubling the dose to 5Omg twice daily had no clear dose-related effect on total exercise time or exercise time to 1mm ST-segment depression, but resulted in a dose-related decrease in RPP at maximum workload (Rodrigues et al. 1986). A more recent study has shown that carvedilol 2Omg once daily reduced the frequency, magnitude and duration of ST-segment depression in Japanese patients with exertional angina; these effects persisted for 24 hours after drug administration (Kishidaetal. 1990). Studies comparing the efficacy of twice daily carvedilol 25mg and slow release nifedipine 2Omg have shown that both drugs improved exercise tolerance, time to onset of angina and time to 1mm ST-segment depression in patients with chronic stable angina after 4 weeks (table V). Consumption of nitroglycerin (glyceryl trinitrate) or number of angina attacks were similar in both groups (van der Does et al. 1991). In another study, carvedilol appeared to maintain its effect on total exercise time and time to 1 mm ST-segment depression over a 6month treatment period; in contrast, the greater initial effect seen in patients receiving propranolol + isosorbide dinitrate (80 + 2Omg twice daily) had disappeared after 6 months (Nahrendorf et al. 1992). 3.3 Congestive Heart Failure -Blocking drugs have been contraindicated in patients with uncompensated congestive heart failure because of their negative inotropic properties. However, beneficial effects (improvement in left ventricular performance) have been reported in patients with congestive heart failure treated with -blockers (Engelmeier et al. 1985; Gilbert et al. 1990; Moser 1993). Because of its dual mechanism of action, carvedilol has potential benefits for patients with congestive heart failure; its ß-blocking activity providing protection from the adverse effects of sympathetic stimulation and its vasodilating activity counterbalancing any acute adverse haemodynamic effects (Bristow et al. I992b; Olsen et al. 1991, 1992; Ruffolo et al. 1992). Data from 12 patients with congestive heart failure (NYHA class II or III) secondary to ischaemic heart disease show that carvedilol 12.5 to 5Omg twice daily for 8 weeks improved exercise time (from 4.3 to 7.1 minutes, p<0.0001) and rest- 252 ing left ventricular ejection fraction (from 27 to 31%, p<0.02) while significantly (p<0.05) reducing total systemic resistance, heart rate and pulmonary arterial wedge pressure compared with baseline measurements (DasGupta et al. 1990). Exercise ejection fraction and cardiac index were not altered significantly and left ventricular volume tended to decrease at rest and during exercise. The negative inotropic effects typically seen in patients with congestive heart failure treated with ß-blockers may therefore be reduced with carvedilol because of its additional vasodilating properties. 4. Tolerability Results of a postmarketing surveillance study involving 2226 hypertensive patients (83% of patients received carvedilol 25mg once daily as maintenance monotherapy) treated for 12 weeks have shown that carvedilol is well tolerated when administered as a once daily 25mg dose (Cauchie et al. 1992). Adverse events caused the withdrawal of therapy in 7% (n = 164) of patients, 3% (65) withdrew because of lack of efficacy and 1% (20) withdrew for other reasons. The most common adverse events causing discontinuation of treatment were vertigo (1.7%), headache .(1.4%), and bronchospasm, fatigue and skin reactions (each 0.5%). The incidence of adverse events appears to be dose-related. Rittinghausen (1988) reported that 8% of patients receiving 25mg once daily as maintenance monotherapy experienced at least 1 adverse event compared with 31 and 29% of patients who received 50 or lOOmg daily doses, respectively. In longer clinical trials in which treatment was given for at least 12 months, adverse effects appeared to decrease with time, particularly when treatment exceeded 2 months, in part due to the patient dropout effect (data on file, Smith-Kline Beecham Pharmaceuticals). In patients 64 years of age, orthostatic hypotension has been uncommon (< 2% of patients) with carvedilol, although dizziness was more common in older subjects than in those 64 years (Moser 1993). Dizziness in the elderly has been reported much less frequently in studies which used the Drugs 45 (2) 1993 12.5mg once-daily regimen for the first 2 days. This was confirmed by the previously referred to postmarketing study (Cauchie et al. 1992), in which 6.9% of patients 65 years reported adverse events suggesting hypotension, versus 7.5% of those <65 years. Several other adverse events have occasionally been reported in patients treated with carvedilol in clinical studies. These included loose stools/diarrhoea (DasGupta et al. 1992; Lahiri et al. 1987; Rodrigues et al. 1986), dry mouth and mucosal swelling (Meyer-Sabellek et al. 1987), depression (Eggertsen et al. 1984b, 1987), constipation (Ogihara et al. 1987), and itching and/or rash (Ogihara et al. 1987; Schnurr et al. 1987). The potential of carvedilol administered at the recommended therapeutic dosage to induce orthostatic (postural) hypotension or syncope (not uncommon in patients treated with pure vasodilators) is relatively low (<l%; data on file, SmithKline Beecham Pharmaceuticals). In some patients transient orthostatic hypotension has occurred after the first dose (Dupont et al. 1987; Morgan et al. 1987), but in a few patients, most of whom received carvedilol 50 mg/day, symptoms were severe enough to warrant discontinuation of therapy (Louis et al. 1987; Morgan et al. 199Ob; Rittinghausen 1988). Carvedilol does not appear to cause clinically significant alterations in laboratory values (Dupont et al. 1987, 1990; Ehmer et al. 1988; Heber et al. 1987; Meyer-Sabellek et al. 1987; Morgan et al. 1987; Ogihara et al. 1987; Schnurr et al. 1987; Seguchi et al. 1990; von Möllendorff et al. 1986; Woodward et al. 1988) or in electrocardiographic findings (von Möllendorff et al. 1986; Ogihara et al. 1987). 5. Dosage and Administration Most patients with mild-to-moderate essential hypertension respond to an oral carvedilol 25mg dose administered once daily; this may be increased up to 5Omg in single or divided daily doses if necessary. However, it is recommended that all patients receive 12.5mg daily for the first 2 days of therapy, and the total maximum daily dose Carvedilol: A Review should not exceed 5Omg. Elderly hypertensive patients should receive a 12.5mg once daily dose which can be titrated at 2-weekly intervals to a maximum of 50 mg/day. In clinical trials, most patients with stable angina pectoris or congestive heart failure received 12.5 to 5Omg doses administered twice daily. Dosage adjustment is not required in patients with renal impairment. Although carvedilol appears to have no effect on glucose homeostasis, patients with both insulin-dependent and non-insulin-dependent diabetes should be monitored while receiving carvedilol because of the risk of masking acute hypoglycaemia. Carvedilol is not recommended for patients with hepatic dysfunction and is contraindicated in patients with third-degree heart block, uncompensated congestive heart failure, cardiogenic shock, severe bradycardia, or asthma. 6. Place of Carvedilol in Therapy Patients with hypertension are frequently treated with a combination of drugs with different mechanisms of action both to improve blood pressure control over that achievable with monotherapy, and to avoid the unwanted effects of individual pharmacological agents by administering lower dosages of each drug involved. Combined use of a ßadrenoceptor antagonist and a vasodilator has been widely accepted, both for its haemodynamic logic and its clinical efficacy and tolerability. Carvedilol is a ß-adrenoceptor antagonist which also exhibits peripheral vasodilating properties, primarily via α1-adrenergic blockade. At doses which antagonise ß-adrenoceptors, carvedilol reduces blood pressure without the disadvantages seen with some ß-blockers, such as compromised blood flow to individual organs, increased total peripheral resistance, and unfavourable metabolic effects. Similarly, the unwanted effects of vasodilatory agents such as stimulation of neurohormonal counter-regulatory mechanisms, and retention of water and electrolytes are not observed with carvedilol. Thus, carvedilol exhibits 2 complementary pharmacological actions which combine to 253 produce an effective antihypertensive agent with a favourable tolerability profile (see sections 3 and 4). In short term clinical trials in patients with mildto-moderate essential hypertension, carvedilol administered as a single daily 25mg dose markedly lowered blood pressure primarily via a reduction in total peripheral resistance, with only moderate effects on heart rate or cardiac output. Comparable antihypertensive efficacy to other blockers (atenolol, labetalol, metoprolol, propranolol, pindolol), nitrendipine, nifedipine, captopril and hydrochlorothiazide has been observed. Further, when given in combination with hydrochlorothiazide, nicardipine or slow release nifedipine an additive antihypertensive effect was seen compared with blood pressure levels established after monotherapy with individual agents. In addition to its well established antihypertensive efficacy in patients with essential hypertension, its distinctive pharmacological profile makes carvedilol useful in specific populations of hypertensive patients. Thus, in patients with renal impairment, carvedilol preserves renal function without eliciting reflex stimulation of the reninangiotensin-aldosterone system or fluid retention. Carvedilol also does not influence glucose tolerance or carbohydrate metabolism and therefore appears suitable for the treatment of hypertensive patients with non-insulin-dependent diabetes. Furthermore, in vitro and animal studies have shown that carvedilol has cardioprotective and neuroprotective properties that may contribute to its overall efficacy in patients with hypertension, angina pectoris or congestive heart failure. A few clinical studies have demonstrated the benefits of carvedilol in patients with chronic stable angina pectoris. While additional studies in this patient population are warranted, results thus far indicate that exercise tolerance and time to onset of angina are increased, and number of anginal episodes and consumption of nitroglycerin are reduced in patients treated with carvedilol. ß-Adrenergic antagonists are usually avoided in patients with heart failure as their propensity to reduce cardiac output may be detrimental. However, preliminary data Drugs 45 (2) 1993 254 show that carvedilol improved several measures of left ventricular function in patients with congestive heart failure (NYHA class II or III) secondary to ischaernic heart disease. Thus, the use of carvedilol with its combined vasodilating and ß-adrenoceptor blocking properties has potential benefits in patients with congestive heart failure; further studies are required to clearly establish the role of carvedilol in this patient group. A postmarketing surveillance study has shown that carvedilol 25mg administered once daily is well tolerated, its -adrenoceptor antagonist properties reducing tachycardia and oedema caused by vasodilation while its vasodilatory activity reduces myocardial depression and decreased regional blood flow. Unlike some 'pure' ß-blockers, such as atenolol or metoprolol, carvedilol appears to have few adverse effects on plasma lipid and lipoprotein levels. Thus, the pharmacological profile of carvedilol, combining ß-adrenergic antagonism and peripheral vasodilation primarily via 1-adrenergic blockade, distinguishes it from most agents currently used in the treatment of hypertension, including 'pure' ßadrenergic blockers and vasodilators. 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