Norethindrone acetate
NEA 5 mg daily is approved by the FDA to treat endometriosis.1 NEA was approved at a time when large controlled clinical trials were not routinely required for a medicine to be approved. The data to support NEA treatment of pelvic pain caused by endometriosis is based on cohort studies. In a study of 194 women, median age 21 years with moderate to severe pelvic pain and surgically proven endometriosis, the effect of NEA on pelvic pain was explored.2 The initial dose of NEA was 5 mg daily. If the patient did not achieve a reduction in pelvic pain and amenorrhea on the NEA dose of 5 mg daily, the dose was increased by 2.5 mg every 2 weeks, up to a maximum of 15 mg, until amenorrhea and/or a decrease in pelvic pain was achieved. Ninety-five percent of the women in this cohort had previously been treated with an estrogen-progestin contraceptive or a GnRH antagonist and had discontinued those medications because of inadequate control of pelvic pain or because of side effects of the medication.
In this large cohort, 65% of women reported significant improvement in pelvic pain, with a median pain score of 5 before treatment and 0 following NEA treatment. About 55% of the women reported no side effects. The most commonly reported side effects were weight gain (16%; mean weight gain, 3.1 kg), acne (10%), mood lability (9%), hot flashes (8%), depression (6%), scalp hair loss (4%), headache (4%), nausea (3%), and deepening of the voice (1%). (In this study women could report more than one side effect.)
In another cohort study of 52 women with pelvic pain and surgically confirmed endometriosis, NEA treatment resulted in pain relief in 94% of the women.3 Breakthrough bleeding was a common side effect, reported by 58% of participants. The investigators concluded that NEA treatment was a “cost-effective alternative with relatively mild side effects in the treatment of symptomatic endometriosis.” A conclusion which I endorse.
NEA has been reported to effectively treat ovarian endometriomas and rectovaginal endometriosis.4,5 In a cohort of 18 women who had previously had the surgical resection of an ovarian endometriosis cyst and had postoperative recurrence of pelvic pain and ovarian endometriosis, treatment was initiated with an escalating NEA regimen.4 Treatment was initiated with NEA 5 mg daily, with the dosage increased every 2 weeks by 2.5 mg until amenorrhea was established. Most women achieved amenorrhea with NEA 5 mg daily, and 89% had reduced pelvic pain. The investigators reported complete regression of the endometriosis cyst(s) in 74% of the women. In my experience, NEA does not result in complete regression of endometriosis cysts, but it does cause a reduction in cyst diameter and total volume.
In a retrospective cohort study, 61 women with pelvic pain and rectovaginal endometriosis had 5 years of treatment with NEA 2.5 mg or 5.0 mg daily.5 NEA treatment resulted in a decrease in dysmenorrhea, deep dyspareunia, and dyschezia. The most common side effects attributed to NEA treatment were weight gain (30%), vaginal bleeding (23%), decreased libido (11%), headache (9%), bloating or swelling (8%), depression (7%), and acne (5%). In women who had sequential imaging studies, NEA treatment resulted in a decrease in rectovaginal lesion volume, stable disease volume, or an increase in lesion volume in 56%, 32%, and 12% of the women, respectively. The investigators concluded that for women with rectovaginal endometriosis, NEA treatment is a low-cost option for long-term treatment.
In my practice, I do not prescribe NEA at doses greater than 5 mg daily. There are case reports that NEA at a dose of ≥10 mg daily is associated with the development of a hepatic adenoma,6 elevated liver transaminase concentration,7 and jaundice.8 If NEA 5 mg daily is not effective in controlling pelvic pain caused by endometriosis, I stop the NEA and start a GnRH analogue, most often elagolix.
NEA 5 mg is not FDA approved as a contraceptive. However, norethindrone 0.35 mg daily, also known as the “mini-pill”, is approved as a progestin-only contraceptive.9 NEA is rapidly and completely deacetylated to norethindrone, and the disposition of oral NEA is indistinguishable from that of norethindrone.1 Since norethindrone 0.35 mg daily is approved as a contraceptive, it is highly likely that NEA 5 mg has contraceptive properties if taken daily.
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