Influence of aspirin on the pharmacokinetics of norethindrone

An investigation into the effect of tenidap sodium on the pharmacokinetics of a combined oral contraceptive

1. The effects of tenidap sodium and placebo on the pharmacokinetics of a combined oral contraceptive (Microgynon 30) were evaluated in 18 healthy premenopausal women in a double-blind, cross-over study lasting two menstrual cycles. 2. Tenidap (120 mg day-1) or placebo was given for 11 days, starting within 4 days of menstruation and Microgynon 30, containing levonorgestrel (150 micrograms) and ethinyloestradiol (30 micrograms), was administered on day 10 of tenidap therapy. 3. The mean maximum plasma levonorgestrel concentrations (Cmax), time to Cmax (tmax) and area under the plasma time-concentration curves (AUC(0,t)) did not differ between subjects given tenidap or placebo. The Cmax, tmax and AUC(0,t) values for ethinyloestradiol did not differ between tenidap and placebo recipients. Only the ethinyloestradiol Cmax showed a significant difference (P = 0.02) between menstrual cycles 1 and 2 (252.9 pg ml-1 and 271.3 pg ml-1, respectively). 4. Co-administration of tenidap and Microgynon 30 was well tolerated and no subject withdrew from the study because of side-effects. There were no side-effects considered to be related to tenidap and no clinically significant laboratory abnormalities were considered to be related to treatment. 5. The results of the study suggest that the pharmacokinetics of the oestrogen and progestin components of the oral contraceptive Microgynon 30 are unlikely to be affected by concomitant administration of tenidap.