Analgesic

The major classes

Paracetamol and NSAIDs

The exact mechanism of action of paracetamol/acetaminophen is uncertain, but it appears to be acting centrally. prostaglandin production; this reduces pain and also inflammation (in contrast to paracetamol and the opioids).^{[citation needed]}

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.^{[citation needed]} 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

Main article: COX-2 inhibitor

These drugs have been derived from NSAIDs. The 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data indicated increased risk of cardiac and cerebrovascular events with these drugs, and rofecoxib was subsequently withdrawn from the market.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

partial agonists 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 macrogol-containing or co-danthramer) are typically co-prescribed.

When used appropriately, opioids and similar narcotic analgesics are otherwise 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. anticonvulsants 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 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 be prescribed together.[1]

Topical or systemic

Topical analgesia is generally recommended to avoid systemic side-effects. Painful joints, for example, may be treated with an Lidocaine is also used for painful mouth sores and to numb areas for dental work and minor medical procedures.

Psychotropic agents

mexiletine and other local anaesthetic analogues.

Atypical and/or adjuvant analgesics

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, dextroamphetamine, and cocaine work against heavy sedation and may elevate mood in distressed patients as do the antidepressants. A well-accepted benefit of THC to chronic pain patients on opioids is 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 addictions 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 [2].

See also

• Pain management
• Patient-controlled analgesia
• Co-proxamol

References

• Cancer pain relief and palliative care. Report of a WHO expert committee [World Health Organization Technical Report Series, 804] . Geneva, Switzerland: World Health Organization; 1990. pp. 1–75. ISBN 92-4-120804-X.
• Bandolier pain site (Oxford pain group)

v • d • e Antihistamines