Drug Interactions between ethinyl estradiol / ethynodiol and relugolix

GENERALLY AVOID: Coadministration of hormonal contraceptives may decrease the efficacy of the fixed-dose oral formulation of relugolix, estradiol, and norethindrone when used for the management of uterine fibroids in premenopausal women. The effect of progestin-only contraceptives is unknown. Relugolix is an orally active gonadotropin-releasing hormone (GnRH) receptor antagonist that inhibits endogenous GnRH signaling by binding competitively to GnRH receptors in the pituitary gland. Administration of relugolix results in dose-dependent suppression of luteinizing hormone (LH) and follicle-stimulating hormone (FSH). This leads to decreased levels of the ovarian sex hormones estradiol and progesterone, and reduction of heavy menstrual bleeding in women with uterine fibroids. It has been suggested that uterine fibroid growth may be stimulated by estrogen and progesterone via paracrine mechanisms. However, combination with estradiol and norethindrone at doses lower than those used in combined hormonal contraceptives have been demonstrated in clinical studies to reduce hypoestrogenic effects and preserves bone mineral density. In addition, concomitant use of estrogen-containing hormonal contraceptives may lead to an increased risk of estrogen-related adverse effects such as breast tenderness/breast pain, abdominal pain, headache, edema, and arterial or venous thromboembolism.

MANAGEMENT: It is recommended that hormonal contraceptives (particularly those containing estrogen) should be discontinued prior to starting treatment with the fixed-dose oral formulation containing relugolix, estradiol, and norethindrone (brand name Myfembree). Some authorities consider their concomitant use to be contraindicated (UK). The manufacturer of Myfembree recommends using effective non-hormonal contraception during treatment and for one week after the final dose. Input from a gynecologist or similar expert on adequate contraception, including emergency contraception, should be sought as needed.

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