Category:Analgesics: Difference between revisions

The relief of pain is among the oldest aims of medicine. Willow bark, rich in salicin, was used as a remedy for pain and fever by Sumerian and Egyptian healers more than three thousand years ago, and was later described by Greek and Roman physicians.<ref name="montinari2019">Montinari MR, Minelli S, De Caterina R. The first 3500 years of aspirin history from its roots — a concise summary. ''Vascul Pharmacol.'' 2019;113:1–8. PMID 30391545.</ref> In 1763 the English clergyman Edward Stone reported to the Royal Society on dried willow bark as a treatment for fever — the first such account in a Western medical journal — beginning the chain of investigation that would lead, more than a century later, to [[aspirin]].<ref name="montinari2019"/>

'''Analgesics''' — medicines used to relieve pain — do not form a single pharmacological class. They are conventionally grouped into several distinct families: the [[non-steroidal anti-inflammatory drugs]], [[paracetamol]] (acetaminophen), the [[opioids]], a group of adjuvant medicines used mainly for neuropathic pain, and the [[muscle relaxants]], which relieve certain kinds of pain indirectly.

Paracetamol (also called acetaminophen) was first synthesized by Joseph von Mering in 1893, though it did not come into wide clinical use until the mid-twentieth century.<ref name="przybyla2021">Przybyła GW, Szychowski KA, Gmiński J. Paracetamol — an old drug with new mechanisms of action. ''Clin Exp Pharmacol Physiol.'' 2021;48(1):3–19. PMID 32767405.</ref> It relieves pain and reduces fever but has little anti-inflammatory effect, and for that reason is generally not classed as an NSAID.

Through the twentieth century a large family of '''non-steroidal anti-inflammatory drugs''' (NSAIDs) was developed, including [[ibuprofen]], [[naproxen]], and [[diclofenac]], alongside aspirin. A major advance in understanding came in the early 1970s, when John Vane and colleagues reported that aspirin and similar medicines inhibit the cyclooxygenase (COX) enzyme, reducing the synthesis of prostaglandins — signalling molecules involved in pain, fever, and inflammation. This work was later recognized with a Nobel Prize.<ref name="vane1971">Vane JR. Inhibition of prostaglandin synthesis as a mechanism of action for aspirin-like drugs. ''Nat New Biol.'' 1971;231(25):232–235. PMID 5284360.</ref> Two principal forms of the enzyme, COX-1 and COX-2, were identified in the early 1990s.

'''Antispasmodics''' — including [[cyclobenzaprine]], [[methocarbamol]], [[carisoprodol]], [[metaxalone]], and [[chlorzoxazone]] — are used mainly for musculoskeletal conditions such as acute low back pain. '''Antispastics''' — including [[baclofen]] and [[dantrolene]] — are used for spasticity arising from neurological conditions such as multiple sclerosis and spinal cord injury. A few agents, such as [[tizanidine]], are used in both roles.<ref name="witenko2014"/>

Opioids bind opioid receptors — especially the µ-opioid receptor — in the nervous system; the relationship between this binding and their analgesic and other effects is addressed in [[:Category:Opioids]]. The skeletal muscle relaxants are a varied group whose mechanisms are not all well established; [[baclofen]], for example, is understood to act at GABA receptors in the spinal cord, but the detail of its action as a muscle relaxant is described in the literature as incompletely understood.<ref name="witenko2014"/> Adjuvant analgesics — including certain antidepressants and anticonvulsants — are used mainly for neuropathic pain.

The analgesics include the [[:Category:NSAIDs]] (such as [[aspirin]], [[ibuprofen]], and [[naproxen]]), [[paracetamol]] (acetaminophen), the [[:Category:Opioids]] (such as [[morphine]], [[oxycodone]], and [[fentanyl]]), and the [[:Category:Muscle relaxants]]. Further agents are used for specific pain syndromes — including triptans, ergot derivatives, and gepants for migraine, and certain antidepressants and anticonvulsants as adjuvants for neuropathic pain. The list is not exhaustive.