Pharmacokinetics and endometrial tissue levels of progesterone after administration by intramuscular and vaginal routes: a comparative study

To determine pharmacokinetic and endometrial effects of vaginally delivered micronized P.

Functionally agonadal estrogen-replacement recipients received either micronized P administered vaginally or bi-daily IM injections of P. Hourly blood samples were obtained, from baseline to 6 hours after the initial dose of P and again on simulated cycle day 21 when transvaginal ultrasound (US) measurements and tissue samples of the endometrium were performed. Blood and tissue samples were assayed for P. Endometrial histology, estrogen receptor (ER) and P receptor (PR) contents were evaluated.

University of Southern California School of Medicine, Los Angeles, California.

Twenty functionally agonadal and four normally ovulating women.

Delivery differences were assessed by [1] endometrial P concentrations; [2] USs; [3] histologic datings; [4] ER and PR contents, and [5] serum P levels.

Endometrial P concentrations were higher with vaginally administered P than endometrial concentrations observed in normal ovulatory women or women who consistently had the highest serum P after IM administration (11.50 +/- 2.60 versus 1.40 +/- 0.40 versus 0.30 +/- 0.10 ng/mg protein [36.56 +/- 8.27 versus 4.45 +/- 1.27 versus 0.95 +/- 0.32 nmol/L], respectively). After 7 days of P, no differences between either treatment regimen and control groups were detected by histologic, ultrasonographic, or immunocytochemical receptor analyses.

Vaginal micronized P enhances P delivery to the uterus compared with a standard IM regimen and results in a synchronous secretory endometrial histology in agonadal women preparing for embryo donation.