Intermittent progestin administration as part of hormone replacement therapy: long-term comparison between estradiol 1 mg combined with intermittent norgestimate and estradiol 2 mg combined with constant norethisterone acetate.

Background: To decrease exposure to progestin during hormone replacement therapy (HRT), a novel oral regimen consisting of constant 17beta-estradiol (E2) daily plus intermittent norgestimate (NGM) has been developed.

Methods: A multicenter study compared the safety and efficacy of E2 1 mg daily plus intermittent NGM 90 micro g (3 days off, 3 days on) (n = 150) vs. a continuous oral dose of E2 2 mg plus norethisterone acetate (NETA) 1 mg (n = 172) daily, for a period of 2 years. Endometrial biopsies were performed at 1 and 2 years. Subjects recorded the occurrence of vasomotor symptoms, uterine bleeding, and adverse events on diary cards.

Results: At 2 years' follow-up, no subject had developed endometrial hyperplasia or cancer. Endometrial atrophy was seen in 75% of subjects using the intermittent NGM regimen and in 78% of women using the constant NETA regimen. Both groups maintained a 96% reduction in vasomotor symptoms up to 2 years. The rates of bleeding and/or spotting showed no difference between the groups, and at 2 years' follow-up, 73% of women in the intermittent NGM group and 83% of subjects in the constant NETA group were amenorrheic. There was a lower incidence of progestin-associated side-effects, such as abdominal discomfort, edema, painful bleeding episodes, and breast symptoms, with the intermittent progestin regimen vs. the constant progestin regimen. Intermittent NGM use was associated with an elevation in HDL- and HDL2-cholesterol, whereas constant NETA reduced these lipoproteins.

Conclusions: The intermittent administration of a progestin, such as NGM, provides a new, well-tolerated regimen to achieve endometrial safety, an adequate rate of amenorrhea, and effective reduction of vasomotor symptoms in postmenopausal women.