POTENTIATION BY CAFFEINE OF THE ANALGESIC EFFECT OF ASPIRIN IN THE PAIN-INDUCED FUNCTIONAL IMPAIRMENT MODEL IN THE RAT

The ability of caffeine to potentiate the analgesic effect of aspirin was studied in the pain-induced functional impairment model in the rat . Female Wistar rats received an intra-articular injection of 30% uric acid in the right hind limb, inducing its dysfunction. Once the dysfu nction was complete, animals received aspirin oral doses of 0, 0.55, 0 .98,and 1.74 mmol/kg with and without 0.17 mmol/kg of caffeine, and th e recovery of functionality over time was considered as an expression of analgesia. Blood samples were drawn simultaneously with hind limb f unctionality determinations, and plasma concentrations of aspirin, sal icylic acid, and gentisic acid were measured by high-performance liqui d chromatography. Aspirin induced a dose-dependent analgesic effect. C affeine alone was ineffective. However, caffeine significantly increas ed the analgesic effect of aspirin at all doses, without modifying asp irin, salicylic acid, or gentisic acid plasma levels. It is concluded that caffeine potentiates the analgesic effect of aspirin by a pharmac odynamic, but not by a pharmacokinetic mechanism.