CYP3A4 Inducers: Drugs or herbal products that induce certain enzymes, including CYP3A4, may decrease the effectiveness of COCs or increase breakthrough bleeding. Some drugs or herbal products that may decrease the effectiveness of hormonal contraceptives include barbiturates, bosentan, felbamate, griseofulvin, oxcarbazepine, and topiramate. Counsel women to use an alternative method of contraception or a back-up method when moderate or weak enzyme inducers are used with COCs, and to continue back-up contraception for 28 days after discontinuing the enzyme inducer to ensure contraceptive reliability.
Dienogest is a substrate of CYP3A4. Women who take medications that are strong CYP3A4 inducers (for example, carbamazepine, phenytoin, rifampicin, and St. John’s wort) should not choose Estradiol Valerate and Estradiol Valerate/Dienogest as their oral contraceptive while using these inducers and for at least 28 days after discontinuation of these inducers due to the possibility of decreased contraceptive efficacy.
The effect of the CYP3A4 inducer rifampicin was studied in an open-label, non-randomized, single center study in 16 healthy postmenopausal women. All volunteers received a treatment regimen of 2 mg estradiol valerate and 3 mg dienogest combination tablets, dosed once daily over 17 days, and of rifampicin, which was administered once daily in an oral dose of 600 mg on Days 12 to 16. 24–hr pharmacokinetics of estradiol and dienogest on Days 11 and 17 were compared. Co-administration of rifampicin with estradiol valerate/dienogest tablets led to a 52 % and 83% decrease in the mean Cmax and AUC(0–24hr), respectively, for dienogest and a 25% and 44% decrease in Cmax and AUC(0–24hr), respectively, for estradiol at steady state.
Strong CYP3A4 Inhibitors: Strong CYP3A4 inhibitors such as ketoconazole increase hormone serum concentrations. The effect of a strong CYP3A4 inhibitor, ketoconazole, on dienogest and estradiol pharmacokinetics was studied in an open-label, two parallel-groups, one-sequence, one-way crossover study in healthy postmenopausal Caucasian women. One tablet of 2 mg estradiol valerate and 3 mg dienogest was administered orally once a day for 14 days. Twelve volunteers received an oral dose of 400 mg ketoconazole (that is, 2 tablets containing 200 mg ketoconazole) once daily for 7 days (Days 8–14). Twenty-four hour pharmacokinetics of estradiol and dienogest on Days 7 and 14 were compared. Co-administration with the strong inhibitor ketoconazole resulted in a 186% and 57% increase of AUC (0–24hr) at steady state for dienogest and estradiol. There was also a 94% and 65% increase of Cmax at steady state for dienogest and estradiol when co-administered with ketoconazole.
Moderate CYP3A4 Inhibitors: Moderate CYP3A4 inhibitors such as erythromycin increase hormone serum concentrations. The effect of a moderate CYP3A4 inhibitor, erythromycin on dienogest and estradiol pharmacokinetics was studied in an open-label, two parallel-groups, one-sequence, one-way crossover study in healthy postmenopausal Caucasian women. One tablet of 2 mg estradiol valerate and 3 mg dienogest was administered orally once a day for 14 days. Twelve volunteers received an oral dose of 500 mg erythromycin three times a day for 7 days (Days 8–14). Twenty-four hour pharmacokinetics of estradiol and dienogest on Days 7 and 14 were compared. When co-administered with the moderate inhibitor erythromycin, the AUC (0–24hr) of dienogest and estradiol at steady state were increased by 62% and 33%, respectively. There was also a 33% and 51% increase of Cmax at steady state for dienogest and estradiol when co-administered with erythromycin.
Other known CYP3A4 inhibitors such as azole antifungals, cimetidine, verapamil, macrolides, diltiazem, antidepressants, and grapefruit juice may increase plasma concentrations of dienogest and estradiol.
HIV/HCV Protease Inhibitors and non-nucleoside reverse transcriptase inhibitors: Significant changes (increase or decrease) in the plasma concentrations of the estrogen and progestin have been noted in some cases of co-administration of HIV/HCV protease inhibitors or with non-nucleoside reverse transcriptase inhibitors.
Antibiotics: There have been reports of pregnancy while taking hormonal contraceptives and antibiotics, but clinical pharmacokinetic studies have not shown consistent effects of antibiotics on plasma concentrations of synthetic steroids.