Effects of capsaicin on the pharmacokinetics of antipyrine, theophylline and quinine in rats.

Capsaicin is the active principal of capsicum fruits, such as hot peppers. The influence of 1-week pretreatment of capsaicin (25 mg kg-1) on the pharmacokinetics of antipyrine, theophylline and quinine was investigated in rats. The drugs were given as an intravenous bolus dose. The control rats received the vehicle solvent (polyethylene glycol) only. Clearance of antipyrine in the capsaicin-pretreated rats was significantly lower than that observed in the control rats (0.241 +/- 0.029 vs 0.344 +/- 0.034 L h-1 kg-1, P < 0.05). This is consistent with a prolongation in the elimination half-life of antipyrine in animals pretreated with capsaicin (2.06 +/- 0.30 vs 1.61 +/- 0.27 h), as the volume of distribution was not significantly changed. In contrast, capsaicin pretreatment had no significant effect on the pharmacokinetics of theophylline and quinine.