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Pain (Medications and their Prescription) 311 MDS Dr. Hesham Khalil, BDS, MSc (Distc), MaxProsth certi, MFDSRCS (England), PhD Definition: Pain is an unpleasant sensation and emotional experience which is associated with actual or potential tissue damage or is described in terms of such damage. Introduction: Pain is not a simple sensation but rather a complex perception, involving higher processing of peripheral nerve signals in the context of other factors, such as previous experience and current mood. The Gate Control Theory (Melazack and Wall, 1965), which incorporates psychological mechanism, remains the major working theory about pain despite the lack of neuro-histological evidence for some of its components. Pain History: The nine important aspects when taking a history from a patient complaining of pain include: 1- Site The patient is asked to point or describe where the pain is felt. It is important to ascertain whether the pain is localized or generalized. 2- Radiation [email protected] 11-12-2006 1 Assess the spread of pain. Sometimes the pain may be felt away from the causative lesion. This is called referred pain. 3- Onset and duration Determine whether the pain is acute or chronic in nature. The patient may the pain to a certain incident or a particular time. 4- Periodicity Continuous or intermittent 5- Character This is best described by the patients own words. It may be sharp, dull, throbbing, stabbing, shooting etc. 6- Severity A visual analogue scale could be helpful 7- Exacerbating factors Hot, cold, sweet, pressure, talking, posture, exercise, etc. 8- Relieving factors e.g. analgesics 9- Associated symptoms Swelling, discharge, bad taste, etc. Pain Mediators: Many types of dental pain arise as a result of infection or damage to tissue. Both events initiate an inflammatory response that is intimately linked with pain. The passage of nociceptive impulses generated in the peripheral nerve fibers depends on the release of various neurotransmitters. These neurotransmitters act either peripherally of centrally. Examples of pain mediators include the following: Plasma kinins: e.g. bradykinin Serotonin Histamine Prostaglandins Leukotrienes [email protected] 11-12-2006 2 Cytokines Neuropeptids Pain is provoked when a variety of substances are released or injected into the tissues. These pain-producing substances can be released by trauma, infection, allergenic reaction, neurogenic reflexes and central changes from cell membranes, mast cells and nerve endings. This leads t the excitation of free nerve endings which act as nociceptors or peripheral sense organs that respond to noxious stimulus. This group of substances include histamine, bradykinin, potassium, acetylcholine, prostaglandins, leukotrienes, and the neuropeptides. Arachidonic acid is derived from cell membrane phospholipids by the action of enzyme phospholipase A2. This enzyme is activated by trauma or infection. Once released, arachidonic acid is acted on by two further enzyme systems. Cyclo-oxygenase activity results in the formation of prostaglandins, thromboxane, and prostacycline, whereas lipo-oxygenae activity results in the production of the leukotrienes. [email protected] 11-12-2006 3 The analgesic effect of aspirin and other NSAIDS is believed t be due to inhibition of cyclo-oxygenase. In addition of their peripheral action, NSAIDS seem to possess a central analgesic action as well. Pain transmission: Free nerve endings which act as nociceptors are present in all orofacial tissues including the skin, oral mucosa, the temporomandibular joint, periodontium, tooth pulp, periosteum and muscles. Bone itself has substance P and clacitonin gene-related peptide containing nerve endings. These become excited by noxious stimuli and the impulses are transmitted via three major classes of nociceptive fibers: 1- C-polymodal fibers. 2- A-delta fibers 3- A-beta fibers Analgesics Aspirin Acetylsalicylic acid Weak organic acid Has been used to treat postoperative pain Pharmacokinetics: rapidly absorbed from the gastrointestinal tract (partially from the stomach and mainly from the upper small intestine). It is hydrolysed to salicylate by esterase enzymes in the gut wall, blood and liver. The half life of aspirin is 20-30 minutes, whereas that of salicylate is 2-3 hours. Salicylate is excreted in the urine as salicyluric acid and glucuronides. In the liver, salicylate is conjugated with glycine and glucuronic acid. [email protected] 11-12-2006 4 Pharmacodynamics: It can inhibit some of the chemical mediators of pain. It irreversibly inhibits the cyclo-oxgenase system by acetylating its active site. Pharmacological properties: 1- Analgesic 2- Anti-inflammatory 3- Antipyretic 4- Antithrombotic Side effects: 1- Gastrointestinal: disturbances, epigastric pain, nausea, gastric erosion. 2- Haemostatic: prolong bleeding time due to impaired platelet aggregation. 3- Tinnitus: due to rise in labyrinthine pressure. 4- Uricosuric: decrease uric acid secretion, which results in an increase in plasma level. 5- Kidney: decrease renal blood in case of underlying circulatory problems such as heart failure and hypertension.. 6- Bronchospasm Drug interactions: aspirin binds firmly to plasma proteins and may displace other drugs from the binding site, especially warfarin, methotreaxte, and sulphonylureas. Reye's syndrome: is a rare disorder occurring in childhood. It involves an acute encephalopathic illness and fatty degeneration of the viscera, especially the liver. Summary (aspirin) Indications: mild to moderate pain, pyrexia, antiplatelet Cautions: Asthma, allergy, impaired renal or hepatic function, dehydration, pregnancy, elderly. [email protected] 11-12-2006 5 Contraindications: children under 12 years, breast feeding (Reye's syndrome), GIT ulceration, haemophilia. Interactions: other NSAIDS (increase side effects) anticoagulats (increase risk of bleeding) antiepiliptics (enhance the effect of phenytoin and valproate) cytotoxic (reduce excretion of metotrexate) Diuretics (antagonism of diuretics effect or reduction in excretion) Metoclopramide and Domperidone (enhance effect of aspirin by increasing absorption) Para-Aminophenols -Paracetmol The active metabolite is N-acetyl-p-aminohhenol (acetaminophen). Pharmacological properties: 1- Analgesics 2- No or little anti-inflammatory 3- Antipyretic Pharmacokinetics: well absorbed from the small intestine after oral ingestion. Plasma level peaks after 30-60 minutes, and the half life is 2 hours. It is conjugated in the liver and excreted in the urine. Side effects: o Safest analgesic! o Skin rash o White blood cell disorders o Hepatotoxicity: at normal dose, paracetamol is broken down in the liver to metabolites that are normally innocuous. In overdose, one of the metabolites accumulates and renders liver cells incapable of synthesizing protein. Acute liver damage can occur after a single dose of 10-12g. [email protected] 11-12-2006 6 Summary (paracetamol) Indications: mild to moderate pain, pyrexia Cautions: impaired renal or hepatic function, alcohol dependence. Interactions: anticoagulants (enhance warfarin) Metoclopamide and Domperidone (accelerate absorption of paracetamol). Non Steroidal Anti-Inflammatory Drugs (NSAIDS) These drugs share many of aspirin's pharmacological properties. They are antiinflammatory and analgesic because they can inhibit the synthesis of ecosanoids. Patients who are hypertensive to aspirin often have a similar reaction when given NSAID. Propionic acid derivatives: Examples of these include ibuprofen, naproxen, flurbiprofen, and ketoprofen. Ibuprofen is rapidly absorbed following oral administration. It binds extensively to plasma proteins. The drug is broken down in the liver and the metabolites excreted in the urine. Ibuprofen and other propionic acid derivatives should be avoided in patients with gastrointestinal disorder, haemostatic problems, or history of hypersensitivity to aspirin. The fenamates: An example of this group is mefenamic acid (Ponstan). It is rabidly absorbed after oral dose. The drug is metabolized in the liver. Half of the metabolites are excreted in the urine and the other half in the faeces. [email protected] 11-12-2006 7 Diflunisal: This is a difluorophenyl derivative of salicylic acid with similar properties of aspirin. It is main advantage is the long plasma half life and low incidence of side effects. Of concern in dentistry is the association between diflunisal and dry socket which could be due to fibrinolysis enhancement. Diclofenac: It is a NSAID derived from phenylacetic acid. It possesses analgesic, antipyretic, and anti-inflammatory properties. Intramuscular perpetration is popular for the relief of moderate to sever pain but related to abscess formation. Interactions of NSAIDS: Examples of the interactions include the followings ACE inhibitors and angiotensin-II antagonists (antagonism of hypotensive effect, increased risk of renal impairment, increased risk of hyperkalemia Other analgesics (with other NSAIDS thee is increased risk of side effects) Antacids (reduce absorption of diflunisal) Antibacterials (some NSAIDS increase the plasma level of gentamycin, possible risk of convulsions with quinolones) Anticoagulants (some NSAIDS enhance the effect of anticoagulants, risk of hemorrhage) Antidepressants (they enhance the effect of NSAIDS) Hypoglycemic drugs (some NSAIDS enhance the effect of sulphonylureas) Antiepileptics (some NSAIDS enhance the effect of phenytoin) Other interactions [email protected] 11-12-2006 8 Doses of some analgesics: Analgesic Aspirin Diflunisal Paracetamol Ibuprofen Flurbiprofen Ketoprofen Naproxen Mefenamic acid Diclofenac Adult dose 600- 1200 mg 4 times a day 500 mg every 12 hours 500-1000 mg every 4 hours 200-600 mg every 4-6 hours 50 mg every 6 hours 25-75 mg every 6 hours 250-500 mg every 12 hours 250 mg every 6 hours 25-75 mg every 8 hours Child dose Nil Nil 120-250 mg every 4 hours 100 mg every 6 hours Nil Nil 125 mg every 12 hours 50 mg every 6 hours Nil You should consult your drug reference for all doses of any drug . Opioid analgesics Opioids analgesics exert their action within the central nervous system by modifying neural activity associated with pain, so they are sometimes referred as centrally acting analgesics. Examples of these analgesics include - Morphine - Codeine - Pethidine Opioid analgesics are used in treating moderate-to-severe postoperative pain. They are metabolized by the liver and excreted by the kidneys. Opioid-induced adverse effects include nausea and vomiting, constipation, decreased respiratory rate and tidal volume, drowsiness, dry mouth, histamine reactions (e.g., urticaria, sneezing, asthma exacerbation, and pruritus), sedation, and mental confusion. Opioids cause slowing of bowel function, thus constipation should be expected whenever opioids are administered. Although rare (incidence is less than 1%), the most worrisome adverse effect of opioids is clinically significant respiratory depression. However, this can be prevented when with close monitoring of patients every 2 hours for the first 24 hours of opioid therapy. Opioid toxicity can occur (rare) in patients receiving chronic opioid therapy and may present as agitation, confusion, nightmares, hallucinations, visual defects, and jerking motions. Usually a reduced dose or change to a different opioid is [email protected] 11-12-2006 9 effective in reducing these symptoms. Because older patients tend to have slower metabolism and excretion of drugs, they are more sensitive to the sedative and respiratory effects of opioids. They are also more likely to have urinary retention, and constipation. These drugs are controlled and prescribed by specialists. In case of overdose naloxone (opioid antagonist) is used to reveres their action. Analgesics and hypertension There are several postulated mechanisms by which analgesics, particularly NSAIDs, could increase blood pressure. These include acute and chronic effects on the kidney (which could lead to salt and fluid retention) and direct vascular effects. NSAIDs also may interact with antihypertensive medications, resulting in increases in blood pressure Principles of prescribing: Good prescribing practice: Medicines should only prescribed when they are essential Written prescription should include: o Full name and address of patient o Full name and address of the doctor o Age of the patient o Quantities of 1 gram should be written as 1g o Quantities f less than 1 gram should be written in mg e.g. 500mg o Dose and dose frequency should be stated o The form of the drug o Names of the drugs and preparations should be clear o Number of days o Exact amount to be supplied o Any blank spaces in the paper should be ruled out. o Any special instructions o Date and signature of the doctor [email protected] 11-12-2006 10 Common abbreviations in prescription: Ac - ante cibum before meals Bid - bis in die twice a day Gtt - gutta a drop Hs - hora somni at bedtime Pc - post cibos after meals PO - per os by mouth Q(*)h -quiaque hora every(*)hours Qid - quarter in die four times a day Tid - three times a day ter in die Example of prescription: Ibuprofen tablets 400 mg One tablet every 6 hours Send: 12 tablets Ibuprofen tablets 400 mg One tablet Qid Send: 12 tablets Prescribing during pregnancy: Medications can have harmful effects on the foetus at any time during pregnancy. Drugs should be prescribed in pregnancy only if the expected benefit to the mother is recognized as being greater than the risk to the foetus, and all medications should be avoided if possible during the first trimester. Few medicines have been shown conclusively to produce congenital malformation (teratogenesis) in humans but no medicine is safe beyond all doubt in early pregnancy. [email protected] 11-12-2006 11 Prescribing during breast feeding: Some medicines may be excreted in the breast milk and may cause toxicity in the infant if administered to nursing mothers. Some drugs can inhibit lactation or sucking reflex of the infant. Prescribing for the elderly: Old people, especially the very old require special care and consideration when they are being prescribed medicines. Poor memory, mental confusion and failing eyesight may lead to poor treatment compliance or medication errors which potentially serious. Drug metabolism and excretion can also be affected with the risk of toxicity. Prescribing for children: When writing prescription for children, it is preferable to state their age. Many of the liquid preparations, particularly suitable for children, contain sugar. Sugar free preparations should be used whenever possible. Prescribing for patient with systemic disease: Notice the patient history and all medications he or she is taking. Consult the patient's physician for further advice. Adverse drug reaction: If you suspect an adverse reaction to a drug the following actions may be taken: Drug should be stopped or changed for an alternative All adverse reaction should be reported Classification of drug reactions: o Type A: those reactions which are predicted from the drug's known pharmacological properties o Type B: those reactions which are not expected from the drug's known pharmacological actions [email protected] 11-12-2006 12 Anaphylaxis: Causes: Drugs: NSAID's, penicillin, anesthetic agents, intravenous colloids Radiographic contrast media Blood product Food Latex Pathophysiology: Release of mediators such as histamine, leukotrienes and prostaglandins from mast cells and basophils Vasodilatation Increase vascular permeability leading to extravasations and edema Respiratory muscle contraction Stimulation of autonomic nervous system Platelet aggregation Recruitment of inflammatory cells Clinical features: (may be some or all) Pruritis Angioedema Urticaria Wheezing Laryngeal edema Hypotension Death !! Within 5-60 minutes Delayed for several hours Biphasic (recurs some hours later) Onset: [email protected] 11-12-2006 13 Management: Medical emergency (needs immediate attention Stop offending agent Administer adrenaline – IM 0.3-0.5 ml of 1:1000 High concentration oxygen Intravenous cannula Intravenous fluid Give intravenous hydrocortisone 100 mg every 6 hours Give H1 (piriton) and H2 (cimetidine) receptor antagonist by intravenous injection Monitor BP, pulse, respiration Prevent recurrence [email protected] 11-12-2006 14