Pharmacokinetic and pharmacodynamic studies of levonorgestrel-releasing intrauterine device.
Level 4 - case-series / case-control
Prospective single-arm pharmacokinetic and pharmacodynamic study without a control group
PubMed 2335100 · doi:10.1016/0010-7824(90)90035-t
What was done
Ten women aged 25 to 34 received an intrauterine device (IUD) releasing 20 µg/day of levonorgestrel (LNG) and were followed for one year. Bleeding and spotting patterns were tracked using menstrual diary cards. Serial blood samples were collected for radioimmunoassays of luteinizing hormone, estradiol (E2), progesterone (P), LNG, and sex hormone-binding globulin (SHBG) three times per week during month 1, and twice per week during months 6 and 12.
What was found
Across 29 evaluated treatment cycles, 44.8% were ovulatory (10 fully ovulatory [type D] and 3 ovulatory with luteal insufficiency [type C]) and 55.2% were anovulatory (13 anovulatory with high follicular activity [type B] and 3 anovulatory [type A]). Serum LNG levels were significantly lower in ovulatory cycles than in anovulatory cycles. Mean serum LNG declined 34.9% from month 1 (492 pmol/l) to month 6 (320 pmol/l). Four women developed amenorrhea in later treatment months, which predominantly coincided with ovulatory hormonal profiles. Two women experienced irregular bleeding with prolonged intermenstrual spotting, and four had regular cycles. Serum LNG correlated with SHBG (r = 0.8856, p < 0.001) and E2 (r = 0.4661, p < 0.05).
Why it matters
This study demonstrates that the contraceptive effect and amenorrhea associated with a 20 µg/day LNG-releasing IUD are primarily driven by local endometrial suppression rather than consistent systemic suppression of ovulation.
Limits
The sample size was very small (n = 10), there was no comparator or control group, and endometrial tissue histology and clinical contraceptive efficacy were not directly measured.
Cited by
- context A levonorgestrel-releasing (progesterone) intrauterine device typically suppresses ovulation during the first two years of use, after which progesterone levels decline and ovulation typically resumes.