Estradiolinteractions

No drug interaction studies have been conducted with CombiPatch. In vitro and in vivo studies have shown that estrogens are metabolized partially by cytochrome P450 3A4 (CYP3A4). Therefore, inducers or inhibitors of CYP3A4 may affect estrogen drug metabolism. Inducers of CYP3A4 such as St. John’s wort ( Hypericum perforatum ) preparations, anticonvulsants (e.g., phenobarbital, phenytoin and carbamazepine), phenylbutazone, and anti-infectives (e.g., rifampin, rifabutin, nevirapine and efavirenz) may reduce plasma concentrations of estrogens, possibly resulting in a decrease in therapeutic effects and/or changes in the uterine bleeding profile. Inhibitors of CYP3A4 such as erythromycin, clarithromycin, ketoconazole, itraconazole, ritonavir, nelfinavir and grapefruit juice may increase plasma concentrations of estrogens and may result in side effects. Adhesion Averaging across 6 clinical trials lasting 3 months to 1 year, of 1,287 patients treated, CombiPatch transdermal systems completely adhered to the skin nearly 90 percent of the time over the 3- to 4-day wear period. Less than 2 percent of the patients required reapplication or replacement of systems due to lifting or detachment. Two patients (0.2 percent) discontinued therapy during clinical trials due to adhesion failure.