The Journal of pharmacy and pharmacology
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J. Pharm. Pharmacol. · Jul 1993
Characterization of the analgesic effect of paracetamol and caffeine combinations in the pain-induced functional impairment model in the rat.
The analgesic activities of paracetamol (100, 178, 316 and 562 mg kg-1), caffeine (10, 18, 32 and 56 mg kg-1) and combinations of these doses were tested on a pain-induced functional impairment model in the rat. Dysfunction of the right hind limb was induced by an intra-articular injection of 30% uric acid in the knee. Drugs were given orally and the recovery of functionality over time was considered as an expression of analgesia. ⋯ Paracetamol plasma levels and analgesic effect observed with administration of 316 mg kg-1 paracetamol alone or 316-32 mg kg-1 of paracetamol-caffeine were fitted to the sigmoidal Emax model according to the Hill equation. The curves obtained were parallel, but that of the combination was shifted to the left. It is concluded that caffeine is able to potentiate the analgesic effect of paracetamol by a pharmacodynamic mechanism, but this only occurs at certain dose combinations.