Mechanism of Action

Progesterone is a naturally occurring steroid that is secreted by the ovary, placenta, and adrenal gland. In the presence of adequate estrogen, progesterone transforms a proliferative endometrium into a secretory endometrium. Progesterone is necessary to increase endometrial receptivity for implantation of an embryo. Once an embryo is implanted, progesterone acts to maintain a pregnancy.

Pharmacokinetics

Absorption

Progesterone serum concentrations increased following the administration of the Endometrin Vaginal Insert in 12 healthy pre-menopausal females. On single dosing, the mean Cmax was 17.0 ng/mL in the Endometrin twice daily group and 19.8 ng/mL in the Endometrin three times daily group. On multiple dosing, steady-state concentrations were attained within approximately 1 day after initiation of treatment with Endometrin. Both Endometrin regimens provided average serum concentrations of progesterone exceeding 10 ng/mL on Day 5. The pharmacokinetic results are summarized in Table 2.

Table 2: Mean (± Standard Deviation) Serum Progesterone Pharmacokinetic Parameters

Distribution

Progesterone is approximately 96 % to 99 % bound to serum proteins, primarily to serum albumin and corticosteroid binding globulin.

Metabolism

Progesterone is metabolized primarily by the liver largely to pregnanediols and pregnanolones. Pregnanediols and pregnanolones are conjugated in the liver to glucuronide and sulfate metabolites. Progesterone metabolites that are excreted in the bile may be deconjugated and may be further metabolized in the gut via reduction, dehydroxylation, and epimerization.

Excretion

Progesterone undergoes renal and biliary elimination. Following injection of labeled progesterone, 50-60% of the excretion of metabolites occurs via the kidney; approximately 10% occurs via the bile and feces. Overall recovery of the labeled material accounts for 70% of an administered dose. Only a small portion of unchanged progesterone is excreted in the bile.

Clinical Studies

Luteal Supplementation During Assisted Reproductive Treatment Study

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