A model to detect interactions between roxithromycin and oral contraceptives

Abstract

Twenty-two healthy women participated in a study to determine whether roxithromycin (a new macrolide antibiotic agent) obtunds the activity of a triphasic oral contraceptive. The duration of the study was four menstrual cycles. Medication was given as follows: (1) cycle 1, no medication to demonstrate ovulation; (2) cycle 2, triphasic oral contraceptive daily to suppress ovulation; (3) cycle 3, triphasic oral contraceptive daily plus roxithromycin, 150 mg b.i.d.; and (4) cycle 4, triphasic oral contraceptive daily plus rifampin, 300 mg daily. Sonography of the ovaries was performed on day 13, and serum progesterone was measured on day 21 of each cycle. Elevated progesterone indicated ovulation. The presence of a maturing follicle supported this finding. All volunteers ovulated in the first cycle and no volunteers ovulated in the second and third cycles. However, 11 women ovulated when rifampin and the triphasic oral contraceptive were given concomitantly. The findings suggest there is no reason to believe that roxithromycin interferes with the efficacy of oral contraceptives.

A pharmacokinetic interaction between roxithromycin and midazolam

“…Roxithromycin has been reported to interact with theophylline, leading to a small but statistically significant increase in the Cm~ and the AUC of theophylline (Houin et al 1992;Saint-Salvi et al 1987). However, it has no clinically significant interaction with cyclosporin, carbamazepine, oral contraceptives, ranitidine or warfarin (Billaud et al 1990;Meyer et al 1990;Paulsen et al 1988;Saint-Salvi et al 1987;Young et al 1989).…”

Drug interactions and hormonal contraception

“…Using the rifampicin studies to illustrate this, the two earlier studies both showed ovulation in some women, 4,5 whereas the two later studies showed no ovulation. 6,7 However, the two earlier studies gave rifampicin for longer (21 days or more) than the later two (10 and 14 days).…”

FFPRHC Guidance (April 2005) Drug interactions with hormonal contraception

“…[63][64][65] Progestogen-only contraception. Evidence for reduced efficacy of POPs with rifampicin is obtained from one small prospective study of nine women using antitubercular treatment (rifampicin and ethambutol).…”