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1 Allergy See also Allergic rhinitis p 393, Allergic conjunctivitis p 464, Eczema p 346, Asthma p 801 Anaphylactic reactions Are severe hypersensitivity reactions with rapid development of life-threatening respiratory and/or circulation problems, often with skin and mucosal changes. Clinical presentation is variable. Triggers include foods (including additives, eg metabisulfite), drugs, insect stings, blood products, latex (eg surgical gloves). Symptoms may appear within minutes to several hours of exposure (eg onset after IV exposure may be faster than after oral exposure). The risk or severity of anaphylactic reactions may be affected by other factors, such as exercise, infections, other diseases (eg asthma), drugs (eg NSAIDs), alcohol. There are no clinically relevant differences between anaphylactic reactions that are allergic (mediated by IgE or other immune complexes) or non-allergic (non-immune mediated). Rationale for drug use Prevention of serious complications and death. Cardiorespiratory support. Symptom relief. Drug treatment See Table 1–1 Management of anaphylaxis p 2 All health care facilities should have an anaphylaxis protocol; refer to this where available. Evidence for treatments used for anaphylactic reactions is derived from clinical practice; trial data are generally lacking. Note that some treatments used may themselves cause anaphylactic reactions, eg volume expanders such as dextran and polygeline (Haemaccel®, Gelofusine®). Adrenaline IM injection into the mid-anterolateral thigh is safe and effective and should be used at the first suspicion of an anaphylactic reaction. When used with volume expansion, adrenaline usually restores BP and cardiac output to acceptable levels; additional vasopressor agents are occasionally indicated. IV adrenaline should only be given by those experienced in its use, with continuous monitoring of ECG, pulse oximetry and BP as it has a high risk of adverse effects. SC route is not recommended because absorption is erratic. Nebulised adrenaline may be useful in upper airway obstruction, eg laryngeal oedema, but should not delay intubation in progressive airway obstruction. First give IM adrenaline 1:1 000 into mid-anterolateral thigh, dose 10 micrograms/kg (0.01 mL/kg) up to maximum 500 micrograms (0.5 mL): • adult, child >50 kg, 500 micrograms (0.5 mL adrenaline 1:1 000) • 40 kg, 400 micrograms (0.4 mL adrenaline 1:1 000) • 30 kg, 300 micrograms (0.3 mL adrenaline 1:1 000) • 25 kg, 250 micrograms (0.25 mL adrenaline 1:1 000) • 20 kg, 200 micrograms (0.2 mL adrenaline 1:1 000) • 15 kg, 150 micrograms (0.15 mL adrenaline 1:1 000) • 10 kg, 100 micrograms (0.1 mL adrenaline 1:1 000) Then • remove cause if practical, eg insect sting, stop an IV infusion • give high flow oxygen (>6 L/minute via face mask) • ensure supine position, with elevated legs if tolerated (if breathing is difficult, allow to sit but not to stand) • establish IV access • maintain airway, breathing and circulation (do not delay intubation in progressive airway obstruction) If hypotensive • give IV sodium chloride 0.9% by rapid infusion: – adult, 1–2 L – child, 20 mL/kg – repeat if inadequate response If inadequate response • continue to give IM adrenaline every 3–5 minutes • if unresponsive to IM adrenaline and ECG monitoring is available, consider IV adrenaline infusion (safer than IV bolus), see local protocols If response still inadequate, consider • nebulised adrenaline for upper airway tract obstruction (stridor) • inhaled (via MDI and spacer) or nebulised salbutamol for lower airway tract obstruction (wheeze) • IV glucagon (p 70) for persistent hypotension in people taking beta-blockers • additional vasopressors for persistent hypotension Monitor • pulse rate, BP, respiratory rate (ECG, pulse oximetry, arterial blood gases if possible) • for 4–6 hours after recovery; extend period if severe or refractory symptoms, history of severe asthma or lifethreatening or biphasic reactions, or possibility of continuing absorption of trigger Glucagon Case reports indicate that glucagon (p 70) may help persistent hypotension in patients on betablockers (who may be refractory to adrenaline). Corticosteroids These have a delayed effect (4–6 hours). Although they are generally used to reduce duration of reaction and prevent relapse, there is no evidence of effectiveness; they may be helpful for asthmatics. They are adjuncts in the management of anaphylaxis and should not be used instead of adrenaline. IV fluids Antihistamines Required to expand intravascular volume and restore BP in combination with adrenaline. There is no evidence that H1 antagonists (eg promethazine) and H2 antagonists (eg ranitidine) are effective in acute anaphylaxis (parenteral promethazine may worsen condition). They are adjuncts helpful for associated urticaria, angioedema and itch. Beta2 agonists Inhaled (via MDI and spacer) or nebulised shortacting beta2 agonists may help relieve bronchospasm that is resistant to adrenaline. 2 Table 1–1 Management of anaphylaxis AMH © 2012 1.1 Sympathomimetics Further management • biphasic reactions, where symptoms recur after apparent recovery, may occur; their incidence is unclear (reported rates range from 1–23%) and there is no way to reliably predict which patients are at risk • serum mast cell tryptase samples may help confirm the diagnosis; collect samples as soon as possible after presentation, and 1–2 hours and 24 hours after symptoms started • after recovery, obtain detailed history of symptoms (particularly timing of exposure to trigger with respect to reaction) and possible triggers; update medical records if necessary; refer patient for specialist review • in people at risk of recurrent anaphylaxis: – provide an action plan and review it regularly; see www.allergy.org.au – provide up to 2 adrenaline autoinjectors if needed and train the person and their carers on their use; ensure they have a repeat supply of the adrenaline autoinjector if it has been used – if a specific trigger is identified from history or skin testing, advise avoiding further exposure and wearing a warning bracelet or necklace – ensure parents of affected children inform all carers of nature of trigger, symptoms and signs of a reaction and its treatment (consider providing a copy of the action plan) – consider risk–benefit of avoiding betablockers as they may make anaphylaxis harder to treat • using an adrenaline autoinjector reduces the need for subsequent doses and hospital admissions for children (data are lacking for adults); effective education may improve poor rate of use • consider immunotherapy (desensitisation) for insect sting allergy 1.1 Sympathomimetics Adrenaline For additional information see Adrenaline p 236 See also Anaphylactic reactions p 2 For drug interactions see Adrenaline p 848 Also known as epinephrine. Indications Anaphylactic reactions Bronchospasm and croup Precautions There are no absolute contraindications to adrenaline in anaphylactic reactions; adrenaline is often life-saving. Dosage See also Table 1–1 Management of anaphylaxis p 2 Anaphylaxis IM route is preferred as it is safer than IV. IV administration may be necessary when response to repeated IM doses and volume AMH © 2012 expansion is inadequate. However, it should only be given by those experienced in its use and with continuous monitoring of ECG, pulse oximetry and BP. IV infusion is safer than slow bolus, which generally should be used for imminent cardiac arrest. IM Adult, child, 10 micrograms/kg (0.01 mL/kg adrenaline 1:1 000) up to 500 micrograms (0.5 mL). Repeat every 3–5 minutes if required. EpiPen®, Anapen® The following doses are recommended by bodies such as the Australasian Society of Clinical Immunology and Allergy; for some children they are higher than the doses recommended by the manufacturer. Repeat dose after 5 minutes if required. Adult, child >20 kg, IM 0.3 mg. Child 10–20 kg, IM 0.15 mg. IV infusion Adult, child, initially 0.1 micrograms/kg/minute, then titrate according to response. Slow IV injection Adult, 50 micrograms (0.5 mL adrenaline 1:10 000). Repeat according to response. Give IV infusion if repeated doses required. Child, initially 1 microgram/kg (0.01 mL/kg adrenaline 1:10 000). Titrate dose according to response. Nebuliser For upper airway tract obstruction, eg laryngeal oedema. Adult, child, up to 5 mL (5 mg) of adrenaline 1:1 000. Croup Neb, 0.5 mg/kg (0.5 mL/kg adrenaline 1:1 000); maximum 5 mg (5 mL). Administration advice Use a 0.5 mL or 1 mL syringe to measure small volumes of adrenaline. Inject IM adrenaline into mid-anterolateral thigh (do not inject into buttocks). For IV bolus, use adrenaline 1:10 000 and give slowly over at least 5 minutes into the side-arm of a fast flowing IV infusion. If 1:10 000 is required and 1:1 000 is the only strength available, dilute 1 mL of 1:1 000 with 9 mL of sodium chloride 0.9% to make a 1:10 000 solution. SC administration is not recommended in anaphylaxis as absorption is erratic. Counselling Make sure anyone who may need to give you adrenaline is taught how to recognise when you need it and how to give it. Call an ambulance as soon as possible after using adrenaline because further doses may be required. Keep your adrenaline autoinjector handy. It needs to be stored in the dark, between 15 and 25C, but not refrigerated; an insulated carry pouch may be needed. Note the use by date for your adrenaline and arrange a new supply in advance. 3 1 1.2 Antihistamines 1 Practice points • ampoules contain 1 mg adrenaline, ie: – adrenaline 1:1 000 = 1 mg in 1 mL – adrenaline 1:10 000 = 1 mg in 10 mL • glucagon may be useful for adrenaline-resistant anaphylaxis in patients on beta-blockers • EpiPen® and Anapen® have different administration techniques; training devices are available to assist with education of patients and carers; a written action plan should be provided inj, 0.1 mg/mL, 10 mL, 10, Adrenaline 1:10 000 (AS, LM) inj, 0.1 mg/mL, 10 mL (syringe), 1, Adrenaline 1:10 000 Min-IJet (CS) inj, 1 mg/mL, 1 mL, 5, 50, Adrenaline 1:1000 (LM), PBS[5]/ DPBS[5] inj, 1 mg/mL, 1 mL, 5, Adrenaline 1:1000 (AS) inj, 150 mcg, 0.3 mL, 1, Anapen Juniora (LM), EpiPen Jra (AL), PBS-A1 inj, 300 mcg, 0.3 mL, 1, Anapena (LM), EpiPena (AL), PBS-A1 1 a anticipated emergency treatment of anaphylaxis, see PBS preloaded injector 1.2 Antihistamines See also Allergic rhinitis p 393, Eczema p 346 Antihistamines are divided into 2 groups: older, sedating drugs and newer, less sedating drugs; they have similar efficacy. Individual response to an antihistamine varies widely; it may be necessary to try a number to see which is best tolerated and most effective. See Table 1–2 Comparison of antihistamines p 5. Practice points • some antihistamines are available with decongestants and/or analgesics for relief of pain, cough, nasal congestion or symptoms of influenza, the common cold and allergies; there is little rationale for these combinations; avoid use 1.2.1 Sedating antihistamines See also Antihistamines p 4 For drug interactions see Antihistamines (sedating) p 853 Cyclizine p 841 Cyproheptadine p 5 Dexchlorpheniramine p 6 Diphenhydramine p 6 Doxylamine p 6 Pheniramine p 6 Promethazine p 7 Trimeprazine p 7 Mode of action Antagonise the action of histamine at H1 receptors, reducing histamine-related vasodilation and increased capillary permeability. They also have anticholinergic activity, some have alpha-blocking activity and some have antiserotonin activity, eg cyproheptadine. Indications Allergic upper respiratory conditions, eg rhinitis Allergic skin conditions, eg urticaria, contact dermatitis Pruritus (including insect bites) Nausea and vomiting Precautions Closed-angle glaucoma, GI obstruction, bladder outlet obstruction (eg prostatic hypertrophy)—may be worsened by the anticholinergic effects of antihistamines. Elderly Avoid use (less sedating antihistamines preferred for allergic conditions) or use a lower dose; increased risk of adverse effects, eg dizziness, sedation, confusion, hypotension, falls, anticholinergic effects. Children Avoid use, particularly in children <2 years (less sedating antihistamines preferred for allergic conditions); increased risk of adverse effects, eg sedation, paradoxical stimulation, anticholinergic effects. Do not use phenothiazine antihistamines (promethazine, trimeprazine) in children <2 years; an association between these antihistamines and sudden infant death syndrome has been suggested but not confirmed. Promethazine may cause fatal respiratory depression. Pregnancy Many of these antihistamines have been used extensively in pregnancy as antiemetics and in treatment of allergic disorders without evidence of fetal adverse effects. Breastfeeding Limited data but short-term use appears safe. Sedation of mother is main concern. Adverse effects Common sedation, dizziness, tinnitus, blurred vision, euphoria, incoordination, anxiety, insomnia, tremor, nausea, vomiting, constipation, diarrhoea, epigastric discomfort, dry mouth, cough Infrequent urinary retention, palpitations, hypotension, headache, hallucinations, psychosis Rare leucopenia, agranulocytosis, haemolytic anaemia, allergic reactions, arrhythmias, dyskinesia, paraesthesia, paralysis, hepatitis Paradoxical stimulation CNS stimulation (excitation, hallucinations, ataxia, seizures) may occur rarely, especially in children, rather than sedation. Counselling This medication may make you sleepy; don’t drive or operate machinery if this happens. Avoid alcohol and other medication that may cause sedation. Practice points • response to a specific antihistamine varies widely, and it may be necessary to try a number of agents to determine which is best tolerated and most effective; response to one member of a class does not predict response to another member of that class • avoid use of antihistamines for the symptomatic treatment of upper respiratory tract infections in young children because of the self-limiting nature of the illness and lack of demonstrated benefit • antihistamines should be stopped at least 4 days before skin-prick testing Sedation, eg premedication 4 AMH © 2012 1.2.1 Sedating antihistamines Table 1–2 Comparison of antihistamines Class/drug Adverse effects Pregnancy Breastfeeding Children Uses Products >2 years allergy, itch tablet, oral liquid >5 years allergy, itch, antiemetic tablet >2 years antiemetic tablet allergy, sedation, insomnia capsule, tablet, oral liquid >12 years insomnia capsule, tablet >2 years allergy, itch, sedation, premedication, antiemetic tablet, oral liquid, injection antiemetic tablet 1 Sedating antihistamines Alkylamines brompheniramine1 chlorpheniramine1 dexchlorpheniramine1 pheniramine fewer sedative and GI adverse effects than other sedating antihistamines; more likely to cause paradoxical CNS stimulation not available as a single ingredient safe safe to use short term Monoethanolamines occasional dose safe dimenhydrinate2 diphenhydramine1 significant sedative effects; low incidence of GI adverse effects safe >2 years (for allergy safe to use short or term sedation) doxylamine1 Phenothiazines promethazine hydrochloride1 promethazine theoclate most anticholinergic antihistamines; safe but significant sedative close effects; may lower seizure avoid to delivery threshold and cause respiratory depression safe to use short term >3 years least sedating of the sedating antihistamines; may increase weight safe to use short >2 years term >2 years (>3 years for sedation) trimeprazine urticaria, itch, sedation in oral liquid children Piperidines cyproheptadine safe allergy, itch tablet Less sedating antihistamines cetirizine desloratadine fexofenadine1 levocetirizine >1 year often better tolerated than sedating antihistamines (reduced sedating and anticholinergic safe effects); cetirizine and levocetirizine most likely to cause sedation safe loratadine1 1 2 tablet, oral liquid, oral drops allergic >6 months rhinitis and conjuncti>6 months vitis, chronic urticaria >12 years tablet >1 year tablet, oral liquid tablet, oral liquid tablet, oral liquid available with decongestants and/or analgesics, see Practice points p 4 in Antihistamines only available combined with hyoscine hydrobromide (p 494) Cyproheptadine Pregnancy Safe to use; Australian category A. For additional information see Sedating antihistamines p 4 For drug interactions see Antihistamines (sedating) p 853 Adverse effects Infrequent Indications Adult, child >7 years, initially 4 mg 3 times daily; maximum 32 mg daily (maximum 16 mg daily if <14 years). 2–6 years, initially 2 mg 2 or 3 times daily; maximum 12 mg daily. Allergic conditions, eg rhinitis, conjunctivitis, urticaria Pruritus Precautions weight gain Dosage Depression—cyproheptadine antagonises serotonin and may occasionally reduce the effectiveness of SSRIs. AMH © 2012 5 1.2.1 Sedating antihistamines 1 Practice points Practice points • cyproheptadine is still marketed for migraine and vascular headache but evidence for efficacy in these indications is limited • used to treat serotonin toxicity, may shorten duration of symptoms; no controlled trials; for moderate-to-severe symptoms a dose of 8 mg every 6–8 hours if needed, has been suggested by some specialists • when used for insomnia: – do not use for >10 consecutive days – can cause daytime sedation, psychomotor impairment and anticholinergic effects; not recommended for elderly people – sedative effect declines with continued use • injection of contents of diphenhydramine capsules (by drug misusers) may result in phlebitis, infection or more serious local effects tab, 4 mg (scored, white), 100, Periactin (AS), PBS-R1 1 prevention of migraine Dexchlorpheniramine For additional information see Sedating antihistamines p 4 For drug interactions see Antihistamines (sedating) p 853 Dexchlorpheniramine is the dextroisomer of chlorpheniramine. Indications Allergic conditions, eg rhinitis, conjunctivitis, urticaria, contact dermatitis Pruritus tab, 50 mg (white), 10, Snuzaid (WD) cap, 50 mg (clear), 10, Snuzaid Gels (WD) cap, 50 mg (blue), 10, Unisom Sleepgels (PP) oral liquid, 2.5 mg/mL, 120 mL, Children’s Paedamin Antihistamine (CP) Doxylamine For additional information see Sedating antihistamines p 4 See also Insomnia p 778 For drug interactions see Antihistamines (sedating) p 853 Indications Short-term management of insomnia Precautions Pregnancy Accepted Safe to use; Australian category A. Precautions Pregnancy Dosage Adult, child >12 years, 2 mg 4 times daily. 6–12 years, 1 mg 4 times daily. 2–6 years, 0.04 mg/kg 3 times daily. tab, 2 mg (scored, white), 20, 40, Polaramine (SH) oral liquid, 0.4 mg/mL, 100 mL, Polaramine Syrup (SH) Diphenhydramine For additional information see Sedating antihistamines p 4 See also Insomnia p 778 For drug interactions see Antihistamines (sedating) p 853 Indications Allergic conditions, eg rhinitis, conjunctivitis, urticaria Sedation (short term) Short-term management of insomnia Precautions Pregnancy Safe to use; Australian category A. Dosage Adult, child >12 years Allergy, 25–50 mg every 4–6 hours as required. Sedation, 50 mg as a single dose. Insomnia, 50 mg at night. Nausea and vomiting in pregnancy Safe to use; Australian category A. Dosage Adult Insomnia, 25–50 mg 30 minutes before bedtime. Nausea and vomiting in pregnancy, initially 12.5 mg at night; increase dose to 12.5 mg twice daily if needed. Practice points • when used for insomnia: – do not use for >10 consecutive days – can cause daytime sedation, psychomotor impairment and anticholinergic effects; not recommended for elderly people – sedative effect declines with continued use tab, 25 mg (scored, white), 20, Dozile (KY), Restavit (WD) cap, 25 mg (purple), 20, Dozile (KY) Pheniramine For additional information see Sedating antihistamines p 4 For drug interactions see Antihistamines (sedating) p 853 Indications 2–6 years Allergic conditions, eg rhinitis, conjunctivitis, urticaria, contact dermatitis Pruritus Motion sickness Nausea, vomiting and vertigo due to Ménière’s disease Allergy, 6.25 mg every 4–6 hours as required. Sedation, 1 mg/kg single dose. Precautions Pregnancy 6–12 years Allergy, 12.5 mg every 4–6 hours as required. Sedation, 1 mg/kg single dose (maximum 50 mg). 6 Safe to use; Australian category A. AMH © 2012 1.2.1 Sedating antihistamines Dosage Motion sickness For motion sickness, take the first dose 30 minutes before travel. Adult, child >10 years, initially, 22.65 mg (half a 45.3 mg tablet) 2 or 3 times daily; up to 45.3 mg 3 times daily. 5–10 years, 22.65 mg (half a 45.3 mg tablet) up to 3 times daily. Adult, child >12 years, oral 25 mg the night before or 2 hours before travel. Repeat dose after 6–8 hours if required. Child >2 years, oral 0.5 mg/kg the night before or 2 hours before travel. Sedation tab, 45.3 mg (scored, white), 10, 50, Avil (AV) Adult, child >12 years, oral 25–75 mg once daily or IM 25–50 mg single dose. Child >2 years, IM/oral 0.5 mg/kg, single dose. Promethazine Premedication Phenothiazine For additional information see Sedating antihistamines p 4 See also Nausea and vomiting p 488 For drug interactions see Antihistamines (sedating) p 853 Adult, IM 25–50 mg 1–2 hours before procedure. Promethazine theoclate Nausea and vomiting Adult, 25 mg 2 or 3 times daily to a maximum of 100 mg; 25 mg at bedtime may be sufficient. Motion sickness Adult, child >10 years, 25 mg 1–2 hours before travel. For long journeys take 25 mg each night beginning the night before travelling. 5–10 years, 12.5 mg given as above. 3–5 years, 6.25 mg given as above. Promethazine theoclate is also known as promethazine teoclate. Indications Allergic conditions, eg rhinitis, conjunctivitis, urticaria, contact dermatitis Pruritus Nausea and vomiting, including motion sickness Sedation, eg for cases of burns, measles, chickenpox Premedication Precautions Phenylketonuria—Gold Cross Antihistamine Elixir® contains aspartame; avoid use. Epilepsy—promethazine lowers the seizure threshold. Respiratory depression—may worsen. Pregnancy Safe to use; avoid close to delivery due to theoretical risk of neurological disturbance in infant; Australian category C. Adverse effects Rare seizures Injection Tissue damage can occur following injection by any route, but can be particularly severe after extravasation or intra-arterial or SC injection. Effects range from pain and burning to thrombophlebitis, paralysis, necrosis and gangrene. See also Administration advice below. Dosage Promethazine hydrochloride Allergy Adult, child >12 years, oral 25–75 mg once daily, or 10–25 mg 2–3 times daily or IM 25–50 mg single dose. Child >2 years, IM/oral 0.125 mg/kg 3 times daily, and 0.5 mg/kg at night. Nausea and vomiting Adult, child >12 years, oral 25 mg or IM 12.5–25 mg every 4–6 hours as needed, maximum 100 mg daily. AMH © 2012 Administration advice Give by deep IM injection. Avoid IV use; if necessary, dilute and give into a large vein at a rate not exceeding 25 mg/minute (avoid extravasation or intra-arterial injection due to risk of severe irritation); stop injection immediately if there is burning, swelling or pain at injection site. Do not give SC (may cause tissue necrosis). Promethazine hydrochloride tab, 10 mg (blue), 50, Fenezal (SZ) tab, 10 mg (blue), 50, Phenergan (AV), PBS-A1/RPBS tab, 25 mg (blue), 50, Fenezal (SZ) tab, 25 mg (blue), 50, Phenergan (AV), PBS-A1/RPBS oral liquid, 1 mg/mL, 100 mL, Gold Cross Antihistamine Elixir (BI) oral liquid, 1 mg/mL, 100 mL, Phenergan Elixir (AV), PBS-A1 inj, 25 mg/mL, 2 mL, 5, Promethazine Hydrochloride (HS), PBS[10]/DPBS[10] 1 palliative care, see PBS Promethazine theoclate tab, 25 mg (scored, white), 10, 30, Avomine (AV) Trimeprazine Phenothiazine For additional information see Sedating antihistamines p 4 For drug interactions see Antihistamines (sedating) p 853 Also known as alimemazine. Indications Urticaria or pruritus, symptom relief Sedation in children Precautions Epilepsy—trimeprazine lowers the seizure threshold. Respiratory depression—may worsen. Diabetes—oral liquid contains 0.68 g/mL sucrose. Pregnancy Safe to use; avoid close to delivery due to theoretical risk of neurological disturbance in infant; Australian category C. 7 1 1.2.2 Less sedating antihistamines 1 Dosage Urticaria or pruritus Adult, child >12 years, 10 mg 3–4 times daily; maximum 100 mg daily. Elderly, 10 mg once or twice daily. Child >2 years, 0.1–0.25 mg/kg 4 times daily; maximum 20 mg daily. Sedation 3–12 years, 1–2 mg/kg at night; maximum 50 mg. oral liquid, 1.5 mg/mL, 100 mL, Vallergan (AV) oral liquid, 6 mg/mL, 100 mL, Vallergan Forte (AV) Cetirizine For additional information see Less sedating antihistamines p 8 Indications Allergic rhinitis and conjunctivitis Chronic urticaria Precautions Allergy to cetirizine, levocetirizine or hydroxyzine— contraindicated (cetirizine is hydroxyzine’s active metabolite). 1.2.2 Less sedating antihistamines Renal See also Antihistamines p 4 Use oral drops in children <2 years as the amount of sorbitol (0.32 g/mL) in the oral liquid may cause diarrhoea. Cetirizine p 8 Desloratadine p 8 Fexofenadine p 9 Levocetirizine p 9 Loratadine p 9 Mode of action Selectively antagonise the action of histamine at H1 receptors. Histamine release causes vasodilation and increases capillary permeability. Indications Allergic rhinitis and conjunctivitis Chronic urticaria Precautions Elderly Increased risk of sedation and anticholinergic effects (but preferred to older sedating antihistamines); monitor carefully. Pregnancy Safe to use although there is more experience with older sedating antihistamines. Desloratadine and loratadine: Australian category B1; cetirizine, fexofenadine and levocetirizine: Australian category B2. Breastfeeding Safe to use. Adverse effects Common or infrequent drowsiness, fatigue, headache, nausea, dry mouth Infrequent elevated liver enzymes, weight gain Rare rash, hypersensitivity (eg anaphylaxis, bronchospasm) Counselling This medication makes some people sleepy; don’t drive or operate machinery if this occurs. Practice points • there is marked individual variation in response to any specific antihistamine; there is no evidence that any one agent is superior • cetirizine and levocetirizine are the most likely of the less sedating antihistamines to cause sedation • antihistamines should be stopped at least 4 days before skin-prick testing 8 Reduce dose if CrCl <30 mL/minute. Children Adverse effects Rare hepatitis, dystonias Dosage Adult 10 mg once daily. Child >6 years, 10 mg once daily or 5 mg twice daily. 2–6 years, 5 mg once daily or 2.5 mg twice daily. 1–2 years, oral drops, 0.25 mg/kg twice daily. Renal impairment Adult, child >6 years, CrCl <30 mL/minute, 5 mg once daily. Counselling Avoid drinking alcohol while taking this medicine. tab, 10 mg (scored, white), 10, 30, Alzene (AL), Zilarex (SZ), Zyrtec (JT), RPBS[30] tab, 10 mg (scored, white), 10, 30, 50, ZepAllergy (IA) tab, 10 mg (scored, white), 10, 30, Zodac (GM), Cetirizine (TX) oral liquid, 1 mg/mL, 75 mL, 200 mL, Zyrtec (JT) oral drops, 10 mg/mL (2.5 mg/5 drops), 20 mL, Zyrtec (JT) Desloratadine For additional information see Less sedating antihistamines p 8 Indications Allergic rhinitis and conjunctivitis Chronic urticaria Precautions Allergy to desloratadine or loratadine—contraindicated. Dosage Adult 5 mg once daily. Child 6–11 years, 2.5 mg once daily. 1–5 years, 1.25 mg once daily. 6–11 months (chronic urticaria), 1 mg once daily. tab, 5 mg (light blue), 7, 28, 42, Aerius (SH) tab, 5 mg (light blue), 7, 28, Claramax (SH) oral liquid, 0.5 mg/mL, 100 mL, Aerius (SH) oral liquid, 0.5 mg/mL, 60 mL, Aerius for Children (SH) AMH © 2012 1.2.2 Less sedating antihistamines Fexofenadine For additional information see Less sedating antihistamines p 8 For drug interactions see Fexofenadine p 889 Indications Dosage Adult Renal impairment CrCl 30–49 mL/minute, 5 mg on alternate days. CrCl 10–29 mL/minute, 5 mg once every 3 days. Allergic rhinitis and conjunctivitis Chronic urticaria Counselling Precautions Renal tab, 5 mg (white), 10, 30, Xyzal (UC) Consider reducing initial dose if CrCl <30 mL/ minute. Loratadine Dosage Adult Rhinitis 120 mg daily in 1 or 2 doses or 180 mg once daily. Urticaria 180 mg once daily. Child 6 months – 2 years, 15 mg twice daily. 2–11 years, 30 mg twice daily. CrCl <30 mL/minute Adult, initially 60 mg once daily. 2–11 years, initially 30 mg once daily. 6 months – 2 years, initially 15 mg once daily. Counselling Oral liquid: you can take this medicine with or without food, but if you take it with a fatty meal, it may not be absorbed as well. tab, 30 mg (peach), 20, Fexal (SZ), Fexotabs (AV), Telfast (AV) tab, 60 mg (peach), 20, Fexotabs (AV) tab, 60 mg (peach), 20, Fexal (SZ), Telfast (AV), RPBS[60] tab, 120 mg (peach), 10, 30, Allerfexo (GM), Fexo (AS) tab, 120 mg (peach), 10, 50, Fexotabs (AV) tab, 120 mg (peach), 10, 20, 30, Tefodine (AS) tab, 120 mg (peach), 10, 30, Fexal (SZ), Telfast (AV), Xergic (AL), RPBS[30] tab, 180 mg (peach), 10, 30, Fexal (SZ), Fexo (AS), Telfast (AV) tab, 180 mg (peach), 10, 50, Fexotabs (AV) tab, 180 mg (peach), 10, 20, 30, Tefodine (AS) tab, 180 mg (scored, yellow), 10, 30, Allerfexo (GM), Xergic (AL) oral liquid, 6 mg/mL, 150 mL, Telfast Children’s Elixir (AV) 1 5 mg once daily. Avoid drinking alcohol while taking this medicine. For additional information see Less sedating antihistamines p 8 Indications Allergic rhinitis and conjunctivitis Chronic urticaria Precautions Allergy to loratadine or desloratadine—contraindicated. Hepatic Reduce starting dose in severe impairment. Dosage Adult, child >30 kg 10 mg once daily. Child 2–12 years, <30 kg, 5 mg once daily. 1–2 years, 2.5 mg once daily. Severe hepatic impairment Adult, initially 5 mg once daily. tab, 10 mg (scored, white), 10, 30, 50, Allereze (AL), Claratyne (SH), Lorano (SZ), RPBS[30] tab, 10 mg (scored, white), 10, 30, 50, Alledine (AS), Allerdyne (GM), Lorastyne (BF), Loratadine (AM, CO) tab, 10 mg (dispersible, white), 10, Claratyne Effervescent (SH) oral liquid, 1 mg/mL, 100 mL, 200 mL, Claratyne (SH) oral liquid, 1 mg/mL, 150 mL, Lorapaed (AE) Levocetirizine For additional information see Less sedating antihistamines p 8 Indications Allergic rhinitis and conjunctivitis Chronic urticaria Precautions Allergy to levocetirizine, cetirizine or hydroxyzine— contraindicated (levocetirizine is the active isomer of cetirizine; cetirizine is hydroxyzine’s active metabolite). Renal Contraindicated if CrCl <10 mL/minute. Reduce dosing frequency if CrCl 10–49 mL/minute. AMH © 2012 9