| Analgesia |
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| analgesics | |
| pain | |
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THE MAJOR CLASSES Paracetamol and NSAIDs The exact mechanism of action of paracetamol/acetaminophen is uncertain, but it appears to be acting centrally. Aspirin and the other NSAIDs inhibit Cyclooxygenase , leading to a decrease in Prostaglandin production; this reduces pain and also Inflammation (in contrast to paracetamol and the opioids). Paracetamol has few side effects, but dosing is limited by possible Hepatotoxicity (potential for Liver damage). NSAIDs may predispose to Peptic Ulcer s, Renal Failure , Allergic Reactions , and Hearing Loss . They may also increase the risk of Hemorrhage by affecting Platelet function. The use of certain NSAIDs in children under 16 suffering from viral illness may contribute to Reye's Syndrome . COX-2 inhibitors See Also: COX-2 inhibitor These drugs have been derived from NSAIDs. The and Celecoxib ) are equally effective analgesics when compared with NSAIDs, but cause less gastrointestinal hemorrhage in particular. However post-launch data indicated increased risk of cardiac and cerebrovascular events with these drugs, and rofecoxib was subsequently withdrawn from the market. The role for this class of drug is Currently hotly debated. Opiates and morphinomimetics Morphine , the archetypal opioid, and various other substances (e.g. Codeine , Oxycodone , Hydrocodone , Diamorphine , Pethidine ) all exert a similar influence on the cerebral Opioid Receptor system. Tramadol and Buprenorphine are thought to be Partial Agonist s of the opioid receptors. Dosing of all opioids may be limited by opioid toxicity (confusion, respiratory depression, Myoclonic Jerks and pinpoint pupils), but there is no dose ceiling in patients who tolerate this. Opioids, while very effective analgesics, may have some unpleasant side-effects. Up to 1 in 3 patients starting morphine may experience Nausea and Vomiting (generally relieved by a short course of Antiemetic s). Pruritus (itching) may require switching to a different opioid. Constipation occurs in almost all patients on opioids, and Laxative s ( Lactulose , Macrogol -containing or Co-danthramer ) are typically co-prescribed. When used appropriately, opioids and similar Narcotic analgesics are safe and effective, carrying relatively little risk of Addiction . Occasionally, gradual tapering of the dose is required to avoid withdrawal symptoms. Specific agents In patients with chronic or neuropathic pain, various other substances may have analgesic properties. Tricyclic Antidepressant s, especially Amitriptyline , have been shown to improve pain in what appears to be a central manner. The exact mechanism of Carbamazepine , Gabapentin and Pregabalin is similarly unclear, but these Anticonvulsant s are used to treat neuropathic pain with modest success. SPECIFIC FORMS AND USES Combinations Analgesics are frequently used in combination, such as the paracetamol and Codeine preparations found in many non-prescription pain relievers. They can also be found in combination with vasoconstrictor drugs such as Pseudoephedrine for Sinus -related preparations, or with Antihistamine drugs for allergy sufferers. The use of paracetamol, as well as aspirin, ibuprofen, naproxen, and other NSAIDS concurrently with weak to mid-range opiates (up to about the hydrocodone level) has been shown to have beneficial synergistic effects by combating pain at multiple sites of action—NSAIDs reduce inflammation which, in some cases, is the cause of the pain itself while opiates dull the perception of pain—thus, in cases of mild to moderate pain caused in part by inflammation, it is generally recommended that the two are prescribed together. {Link without Title} Topical or systemic Topical analgesia is generally recommended to avoid systemic side-effects. Painful joints, for example, may be treated with an Ibuprofen - or Diclofenac -containing gel; Capsaicin also is used topically. Lidocaine and Steroids may be injected into painful joints for longer-term pain relief. Lidocaine is also used for painful Mouth Sore s and to numb areas for Dental work and minor medical procedures. Psychotropic agents Tetrahydrocannabinol (THC) and some other Cannabinoids , either from the '' Cannabis Sativa '' plant or synthetic, have analgesic properties, although the use of cannabis derivatives is illegal in many countries. Other psychotropic analgesic agents include Ketamine (an NMDA receptor antagonist), Clonidine and other α2-adrenoreceptor agonists, and Mexiletine and other local anaesthetic analogues. Atypical and/or adjuvant analgesics Orphenadrine , Cyclobenzaprine , Scopolamine , Atropine , Gabapentin , first-generation Antidepressants and other drugs possessing Anticholinergic and/or Antispasmodic properties are used in many cases along with analgesics to potentiate centrally acting analgesics such as Opioids when used against pain especially of neuropathic origin and to modulate the effects of many other types of analgesics by action in the Parasympathetic Nervous System . Dextromethorphan has been noted to slow the development of tolerance to opioids and exert additional analgesia by acting upon the NMDA receptors; some analgesics such as Methadone and Ketobemidone and perhaps Piritramide have intrinsic NMDA action. The use of Adjuvant analgesics is an important and growing part of the pain-control field and new discoveries are made practically every year. Many of these drugs combat the side effects of opioid analgesics, an added bonus. For example, Antihistamines including orphenadrine combat the release of histamine caused by many opioids, Methylphenidate , Caffeine , Ephedrine , Dextroamphetamine , and Cocaine work against heavy sedation and may elevate mood in distressed patients as do the antidepressants. The one indisputably true benefit of THC to chronic pain patients on opioids may be its superior anti-nauseant action. However, it would make more sense to use the Marinol capsule, or oral, rectal, or vapour administration of hash oil, rather than smoking cannabis, for the same reasons most doctors advise against smoking tobacco. ADDICTION In the United States in recent years, there has been a wave of new Addiction s to prescription narcotics such as Oxycodone (Percocet) and Hydrocodone ( Vicodin , Lortab etc.) when available in pure formulations as opposed to combined with other medications (as in Percocet which contains both oxycodone and acetaminophen/paracetamol). Hydrocodone is only available in pure form in some European countries as the original hydrocodone pharmaceutical, Dicodid tablets. Far from reducing addiction liability, the paracetamol content of many codeine, dihydrocodeine, hydrocodone, and oxycodone pharmaceuticals in the United States only saddles users with the high risk of severe liver damage, and extraction of the opioids with cold water or solvents reduces this problem for the sophisticated abuser, self-medicator, and legitimate prescription holder alike {Link without Title} . SEE ALSO REFERENCES
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