PURPOSE: To investigate if the ordinary use of a vaginal suppository containing miconazole results in systemic absorption that is sufficient to affect the activities of CYP1A2 and CYP3A4, which are major drug- and steroid-metabolising enzymes.
METHODS: In 20 healthy non-pregnant women aged 18-45 years, the serum concentration of miconazole was determined following the use of a vaginal suppository containing 1,200 mg miconazole. Enzyme activities of CYP1A2 and CYP3A4 were determined as metabolic ratios of caffeine (CMR = (AFMU + 1MU + 1MX)/17DMU) and quinidine (QMR = 3-hydroxy-quinidine/quinidine) respectively before and 34 h after insertion of the suppository. Miconazole was analysed by LC-MS/MS, while caffeine and metabolites were analysed by HPLC-UV and quinidine and hydroxy-quinidine were analysed by HPLC fluorescence.
RESULTS: All 20 women had measurable concentrations of miconazole in serum (mean ± SD: 12.9 ± 5.6 μg/L; range: 3.5-24.6 μg/L). Although not statistically significant, an association between the serum concentrations of miconazole and the inhibition of CYP1A2 activity was indicated. No relation was observed between the CYP3A4 activity and the miconazole serum concentration.
CONCLUSIONS: Miconazole is absorbed via the vaginal mucosa to the systemic circulation in measurable concentrations. Our data indicate a concentration-dependent inhibition of CYP1A2, but the effect is negligible compared with the variation in the activity of CYP1A2 and is regarded to be of no clinical significance to the women. However, further studies on the ability of miconazole to be transferred across the placenta or to interfere with the placental function are warranted to secure safe use during pregnancy.