Drug Interactions between clotrimazole and Nuvelle TS Phase I

MONITOR: Azole antifungal agents may increase the plasma concentrations of estrogens and progestins. The mechanism is decreased clearance of the hormones due to inhibition of CYP450 3A4 activity by azole antifungals. Coadministration of voriconazole (200 mg every 12 hours) and an oral contraceptive containing 35 mcg of ethinyl estradiol and 1 mg of norethindrone increased the steady-state peak plasma concentration (Cmax) and area under the concentration-time curve (AUC) of ethinyl estradiol by an average of 36% and 61%, respectively, and Cmax and AUC of norethindrone by 15% and 53%, respectively, in healthy volunteers. Fluconazole doses of 150 mg and 200 mg have also been shown to increase the serum concentrations of ethinyl estradiol and levonorgestrel in healthy women receiving low-dose oral contraceptives, while single and multiple doses of fluconazole 50 mg had no significant effect on the pharmacokinetics of a high-dose oral contraceptive containing 150 mcg ethinyl estradiol and norgestrel 300 mcg. Ironically, there have been isolated reports of breakthrough bleeding and unintended pregnancy during use of oral contraceptives with itraconazole, which would suggest decreased rather than increased effect of the contraceptives. However, the association to itraconazole is questionable.

MANAGEMENT: During concomitant therapy with azole antifungal agents, patients should be observed for increased or altered pharmacologic response to estrogens and progestins, and dosage(s) adjusted accordingly as necessary.

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