Impaired elimination of caffeine by oral contraceptive steroids.

The effect of OCS on the disposition and elimination of caffeine was examined. Caffeine (250 mg) was administered orally to 13 healthy males, nine healthy females taking no OCS, and nine healthy females on OCS. The t1/2 (beta) was significantly prolonged in women on OCS (10.7 +/- 3.0 hr vs. 6.2 +/- 1.6) (p less than 0.001) as compared to women taking no OCS. Women on OCS had a significantly lower total plasma clearance (0.79 +/- 0.21 ml/min/kg vs. 1.3 +/- 0.35) and free clearance (1.12 +/- 0.28 ml/min/kg vs. 1.97 +/- 0.57) that women not taking OCS. Volumes of distribution and plasma binding were similar in both groups of females. When women taking no OCS were compared with men, all pharmacokinetic parameters were similar except for volume of distribution, which was significantly larger in the women (p less than 0.05). We conclude that OCS impair the elimination of caffeine.