Postabortal contraception with norethisterone enanthate injections.

Area of Science:

• Reproductive Endocrinology
• Pharmacokinetics
• Contraception

Background:

• Norethisterone enanthate (NET-EN) is an injectable progestogen used for contraception.
• Understanding its pharmacokinetic profile and ovulation inhibition duration is crucial for effective use.

Purpose of the Study:

• To evaluate the hormonal effects and ovulation inhibition duration of intramuscular NET-EN in women undergoing first-trimester abortion.
• To determine the optimal injection interval for sustained ovulation inhibition.

Main Methods:

• Five women received 200 mg intramuscular NET-EN post-abortion, with repeat injections at 8-week and then 12-week intervals.
• Plasma levels of FSH, LH/hCG, estradiol, progesterone, and norethisterone (NET) were monitored.
• Ovulation was assessed by progesterone levels and follicular activity by estradiol concentrations.

Main Results:

• NET-EN did not impact hCG, estradiol, or progesterone elimination.
• Peak plasma NET concentrations (5.5-11 ng/ml) occurred around day 10, decreasing to 0.18-0.64 ng/ml by 8 weeks.
• Ovulation was inhibited for at least 8 weeks post-injection.
• NET accumulation occurred with 8-week intervals; 12-week intervals led to decreased NET levels and observed ovulation.

Conclusions:

• An injection interval of less than twelve weeks is necessary for consistent ovulation inhibition with NET-EN in this population.
• NET-EN effectively postpones FSH increase and follicular activity until plasma NET levels fall below 3 ng/ml.