Estradiol drug interactions

Ethinyl estradiol is metabolized in the liver via the cytochrome P-450 system. It is metabolized primarily via CYP450 3A4. When reviewing drug interactions of oral contraceptives, it is important to keep in mind that antibiotic administration during contraceptive use may decrease the efficacy of many combined contraceptives. Refer to Table 45-4 for a list of common drug interactions seen with oral contraceptives.1,31... 

ALESSE 28 (levonorgestrel and ethinyl estradiol tablets) Wyeth April 2004 labeling Precautions. Drug Interactions Herbal products containing St. John s wort H. perforatum) may induce hepatic enzymes (CYP) and P-gp transporter and may reduce the effectiveness of contraceptive steroids. This may also result in breakthrough bleeding ... 

Karim A, Schwartz L, Perez A, Cao C. Lack of clinically significant drug interaction in tiie coadministration of pioglitazone witii ethinyl estradiol and noretiiindrone. DiabeUs (2003) 52 (Suppl 1)A123. 

Nevirapine induces and is metabolized by CYP3A4 therefore, coadministration of drugs that induce or are metabolized by this isoenzyme may result in interactions. Nevirapine may decrease the effectiveness of ethinyl estradiol-based contraceptives and can lower plasma concentrations of methadone. Nevirapine should not be administered with ketoconazole, rifampin, or rifabutin. 

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