Effect of caffeine on the oral absorption and disposition of quinidine.

The effect of caffeine on the oral absorption and disposition of quinidine was assessed in nine healthy men. Single 300-mg doses of quinidine sulfate were given by mouth in the absence and presence of caffeine in a crossover study. In the caffeine-treatment phase, 1 g of caffeine was given per day in divided doses for one week before the administration of a second 300-mg quinidine sulfate dose. Blood samples were collected at various times for 24 hours after drug administration, and the sera were assayed for quinidine. Urine specimens were also analyzed for quinidine. No differences were found in the quinidine absorption and disposition constants between the control and caffeine-treated phases, using a nonlinear, least-squares regression analysis of the serum quinidine concentration-time curves and standard blood and urine bioavailability test methods. The hypothesis proposed by previous investigators that quinidine disposition may be altered by caffeine-inducible hepatic microsomal enzymes was not supported by these data. Caffeine treatment at a daily dose of 1 g per day for one week had no apparent effect on the absorption or disposition of quinidine after a single 300-mg oral dose of quinidine sulfate in healthy men.