Topical Analgesics

Counterirritants and rubefacients are irritants that stimulate nerve endings in intact skin to relieve pain in skin (e.g. postherpetic), viscera or muscle supplied by the same nerve root. All produce inflammation of the skin which becomes flushed, hence rubefacients. They are often effective though their precise mode of action is unknown.

The best counterirritants are physical agents, especially heat. Many drugs, however, have been used for this purpose and suitable preparations containing salicylates, nicotinates, menthol, camphor and capsaicin (depletes skin substance P) are also available.

Topical NSAIDs (see p. 290) are used to relieve musculoskeletal pain.

Local anaesthetics. Lidocaine and prilocaine are available as gels, ointments and sprays to provide reversible block of conduction along cutaneous nerves (see p. 422). Benzocaine and amethocaine (tetracaine) carry a high risk of sensitisation.

Volatile aerosol sprays, beloved by sportspeople, produce analgesia by cooling and by placebo effect.

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