Drug Interactions between Estinyl and Viramune

ADDITIONAL CONTRACEPTION RECOMMENDED: Coadministration with nevirapine may decrease the plasma concentrations of contraceptive hormones. The proposed mechanism is nevirapine induction of CYP450 3A4, the isoenzyme partially responsible for the metabolic clearance of sex hormones and other steroids. In ten HIV-positive subjects, nevirapine (200 mg once a day for 2 weeks followed by 200 mg twice a day for 2 weeks) decreased the area under the plasma concentration-time curve (AUC) of ethinyl estradiol (administered as ethinyl estradiol-norethindrone 0.035 mg-1 mg) by 20% compared to administration of the oral contraceptive alone. The AUC and peak plasma concentration (Cmax) of norethindrone decreased by 19% and 16%, respectively.

MANAGEMENT: Women using hormonal contraceptives should be advised of the risk of breakthrough bleeding and unintended pregnancy during concomitant therapy with nevirapine. Alternative or additional methods of birth control should be used during and for at least two weeks after short-term and 4 weeks after long-term (greater than 4 weeks) nevirapine therapy. Some authorities suggest that no dose adjustment of ethinyl estradiol or norethindrone is required when used together for contraception.
-If a combination oral contraceptive pill is used, a regimen containing at least 50 mcg of ethinyl estradiol per day or equivalent should be selected. Although breakthrough bleeding is not necessarily indicative of low ethinyl estradiol serum levels or increased risk of ovulation, some clinicians suggest that women who experience breakthrough bleeding during enzyme-inducing therapy may be prescribed an increased dose of ethinyl estradiol above 50 mcg daily by combining more than one formulation of contraceptive pill if necessary.
-For emergency contraception in patients who have used an hepatic enzyme inducer in the past 4 weeks, a non-hormonal emergency contraceptive (e.g., copper intrauterine device) is considered preferable. If this is not possible, some authorities recommend that the usual dose of levonorgestrel (1.5 mg) should be doubled to 3 mg and taken as a single dose as soon as possible (within 72 hours of unprotected sexual intercourse). However, there are no data on efficacy, compliance, or side effects of this regimen.
-No precautions or recommendations are available for women using hormone-releasing intrauterine systems, but a significant interaction with these systems is thought to be unlikely due to their local action. -Injectable progestin-only contraceptives are also thought to be unaffected by enzyme-inducing drugs.

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