No interaction between ciprofloxacin and an oral contraceptive

Several antibiotics have been reported to lessen the ovarian suppression produced by oral contraceptive agents, as a result of drug interactions. The present investigation was designed to study the likelihood of the occurrence of any such interaction between the fluoroquinolone antibiotic ciprofloxacin (Ciproxin) at a dosage of 500 mg twice a day and the "low-dose" oral contraceptive Marvelon (30 microgram of ethinyl estradiol [EE] plus 150 microgram of desogestrel). Twenty-four healthy female volunteers were studied in a double-blind, placebo-controlled, randomized crossover trial. There were no significant differences between measurements of the area under the concentration-time curve of EE up to 24 h after oral contraceptive intake during placebo and ciprofloxacin administration on days 11 and 16 of the cycles, indicating the absence of pharmacokinetic interaction. Similarly, no clinically significant differences in the levels of sex hormone binding globulin were found between the placebo and ciprofloxacin cycles, indicating no major variation in EE levels during ciprofloxacin and placebo treatment. Ten subjects in each of the placebo and ciprofloxacin groups had early-follicular-phase levels of 17-beta estradiol (<184 ng/liter) at one or more points during their cycles, but none had values above the early-follicular-phase range, indicating no significant ovarian activity. In addition, all subjects had progesterone levels of <2 ng/ml, indicating the absence of ovulation. Only two subjects, who received the placebo, had evidence of sustained follicular growth to a potentially ovulatory follicle ( approximately 18 mm). We conclude that ciprofloxacin does not interfere with the ovarian suppression produced by the low-dose oral contraceptive Marvelon.