Pharmacokinetics, pharmacodynamic and endometrial effects of a single dose of 200 mg norethisterone enanthate

Ovulation was confirmed by daily analyses of the peripheral plasma levels of estradiol (E2)4) and progesterone (P) in a pre-treatment cycle of 14 subjects. An endometrial biopsy was taken either in the proliferative or in the secretory phase of the cycle. On the 5th day of a subsequent cycle 200 mg norethisterone enanthate (NET-EN) was administered intramuscularly. The levels of E2, P and those of NET were analyzed during the next 19 days and again during 44-60 days following the injection. The endometrial biopsy was repeated on the 23rd and 59th day of the treated cycle. The levels of NET reached a peak of 34.3 nmol/1 on the sixth post-injection day and decreased to below detectable limits in 3 of 12 subjects by the end of the observation. Ovarian activity was completely suppressed in all women during the first period, but returned to different levels in 11 subjects during the second. Four of them exhibited ovulatory steroid pattern. The morphologic changes of the endometrium reflected the progestogen effect in the first post-injection period but were characteristic of the ovarian reaction in the second.