Analgesic

An analgesic (colloquially known as painkiller) is any member of the diverse group of drugs used to relieve pain and to achieve analgesia (literally, "absence of pain"). Analgesic drugs act in various ways on the peripheral and central nervous system; they include paracetamol (acetaminophen), the nonsteroidal anti-inflammatory drugs (NSAIDs) such as the salicylates, narcotic drugs such as morphine, synthetic drugs with narcotic properties such as tramadol, and various others. Some other classes of drugs not normally considered analgesics are used to treat neuropathic pain syndromes; these include tricyclic antidepressants and anticonvulsants.

The major classes

Paracetamol and NSAIDs

The exact mechanism of action of paracetamol is uncertain, but it appears to be acting centrally. Aspirin and the NSAIDs inhibit cyclooxygenase, leading to a decrease in prostaglandin production; this improves pain and also inflammation (in contrast to paracetamol and the opioids).

Related Topics:
Aspirin - Cyclooxygenase - Prostaglandin - Inflammation

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Paracetamol has few side effects, but dosing is limited by possible hepatotoxicity (potential for liver damage). NSAIDs may predispose to peptic ulcers, renal failure, allergic reactions, and hearing loss. They may also increase the risk of hemorrhage.

Related Topics:
Hepatotoxicity - Liver - Peptic ulcer - Renal failure - Allergic reactions - Hearing loss - Hemorrhage

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Opiates and morphinomimetics

Tramadol and buprenorphine are thought to be partial agonists of the opioid receptors. Morphine, the archetypical opioid, and various other substances (e.g. pethidine, oxycodone, hydrocodone, diamorphine) all exert a similar influence on the cerebral opioid system. Dosing may be limited by opioid toxicity (confusion, myoclonic jerks and pinpoint pupils), but there is no dose ceiling in patients who tolerate this.

Related Topics:
Tramadol - Buprenorphine - Partial agonist - Opioid receptor - Morphine - Pethidine - Oxycodone - Hydrocodone - Diamorphine

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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 antiemetics). Pruritus (itching) may require switching to a different opioid. Constipation occurs in almost all patients on opioids, and laxatives (lactulose, macrogol-containing or co-danthramer) are typically co-prescribed.

Related Topics:
Nausea - Vomiting - Antiemetic - Pruritus - Constipation - Laxative - Lactulose - Macrogol - Co-danthramer

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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.

Related Topics:
Narcotic - Addiction

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Specific agents

In patients with chronic or neuropathic pain, various other substances may have analgesic properties. Tricyclic antidepressants, especially amitriptyline, have 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 anticonvulsants are used to treat neuropathic pain with modest success.

Related Topics:
Tricyclic antidepressant - Amitriptyline - Carbamazepine - Gabapentin - Pregabalin - Anticonvulsant

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