Drug Interactions between conjugated estrogens / medroxyprogesterone and elagolix

MONITOR: Coadministration with inducers of CYP450 3A4 may decrease the plasma concentrations and pharmacologic effects of medroxyprogesterone, which is primarily metabolized by the isoenzyme. Aminoglutethimide, a CYP450 3A4 inducer, has been shown to significantly decrease the serum levels of medroxyprogesterone by 50% or more when administered at 250 mg two to four times daily to women with breast cancer receiving high-dose medroxyprogesterone orally. The decrease was accompanied by an increase in serum cortisol level, which suggests diminished adrenal suppressive effect of medroxyprogesterone. The interaction has not been studied with depot formulations of medroxyprogesterone. Because the clearance of medroxyprogesterone is approximately equal to the rate of hepatic blood flow, drugs that induce CYP450 3A4 are not expected to significantly affect the pharmacokinetics of medroxyprogesterone administered parenterally. In one study, no interaction was reported when medroxyprogesterone was administered intravenously with aminoglutethimide.

MANAGEMENT: Pharmacologic response to medroxyprogesterone should be monitored more closely whenever a CYP450 3A4 inducer is added to or withdrawn from therapy, and the dosage adjusted as necessary. When administered as the depot formulation for contraception, no dosage adjustment for medroxyprogesterone is currently recommended during coadministration with CYP450 3A4 inducers. However, consideration may be given to decreasing the dosing interval (e.g., from one injection every 12 weeks to every 10 weeks) if an interaction is suspected.

GENERALLY AVOID: Since endometriosis is fueled by estrogen, coadministration with estrogen-containing medications including combination oral contraceptive pills is expected to reduce the efficacy of elagolix. The effect of progestin-only contraceptives is unknown. Elagolix is a gonadotropin-releasing hormone (GnRH) receptor antagonist that inhibits endogenous GnRH signaling by binding competitively to GnRH receptors in the pituitary gland. Administration of elagolix results in dose-dependent suppression of luteinizing hormone (LH) and follicle-stimulating hormone (FSH), leading to decreased levels of the ovarian sex hormones, estradiol and progesterone.

MANAGEMENT: Women requiring contraception should be advised to use non-hormonal forms of contraception during treatment with elagolix and for one week after its discontinuation.