Oral contraceptive steroids impair the elimination of theophylline.

The influence of OCS and sex differences on the disposition of theophylline has been studied in 12 healthy young men (29 +/- 4 years old), 13 healthy young women (29 +/- 12), and 10 healthy young women (24 +/- 3) receiving OCS for a period greater than 6 months. The elimination t1/2 was longer in women taking oral contraceptives (523 +/- 110 min) than in women not on oral contraceptives (386 +/- 157). Weight-normalized plasma clearance of theophylline was less in women taking oral contraceptive steroids (0.70 +/- 0.15 ml X min-1 X kg-1) than in women not on oral contraceptive steroids (0.98 +/- 0.32). Plasma binding and volume of distribution were not different between the two groups of women. Weight-normalized clearance, weight-normalized volume of distribution, plasma t1/2, and plasma binding were not different between men and women not taking OCS.