No interaction between ciprofloxacin and an oral contraceptive

Several antibiotics have been reported to lessen the ovarian suppression pr oduced by oral contraceptive agents, as a result of drug interactions. The present investigation was designed to study the likelihood of the occurrenc e of any such interaction between the fluoroquinolone antibiotic ciprofloxa cin (Ciproxin) at a dosage of 500 mg twice a day and the "low-dose" oral co ntraceptive Marvelon (30 mu g of ethinyl estradiol [EE] plus 150 mu g of de sogestrel). Twenty-four healthy female volunteers mere studied in a double- blind, placebo-controlled, randomized crossover trial. There were no signif icant 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, indicatin g the absence of pharmacokinetic interaction, Similarly, no clinically sign ificant differences in the levels of sex hormone binding globulin were foun d between the placebo and ciprofloxacin cycles, indicating no major variati on in EE levels during ciprofloxacin and placebo treatment. Ten subjects in each of the placebo and ciprofloxacin groups had early-follicular-phase le vels of 17-beta estradiol (<184 ng/liter) at one or more points during thei r cycles, but none had values above the early-follicular-phase range, indic ating no significant ovarian activity. In addition, all subjects had proges terone levels of <2 ng/ml, indicating the absence of ovulation. Only two su bjects, who received the placebo, had evidence of sustained follicular grow th to a potentially ovulatory follicle (similar to 18 mm). We conclude that ciprofloxacin does not interfere with the ovarian suppression produced by the low-dose oral contraceptive Marvelon.