Pharmacokinetics of natural progesterone administered in the form of a vaginal tablet

Our study was conducted to assess the pharmacokinetics of natural progesterone administered in the novel formula of an effervescent vaginal tablet. Fifty post-menopausal women, with a median age of 43.5 years (range 28-55), volunteered to participate in the research. All women discontinued their hormonal replacement therapy 1 month prior to the study. The pharmacokinetics of 50 and 100 mg of progesterone administered as a vaginal tablet were evaluated. After the initial administration of 50 mg or 100 mg, a mean serum Cmax of 20.43 +/- 8.01 nmol/l and 31.61 +/- 12.62 nmol/l (P < 0.0004) was reached at a Tmax of 6.1 +/- 2.63 and 6.4 +/- 3.35 h respectively. The terminal half-life was 13.18 +/- 1.3 and 13.7 +/- 1.05 h respectively. Continuous use of the 100-mg tablet resulted in a mean serum progesterone concentration of 26.08 +/- 13.96 nmol/l and 21.42 +/- 16.32 nmol/l after 14 and 30 days respectively. Women >40 years were found to have a significantly lower Tmax compared to younger women (P = 0.02). The continuous use of vaginal progesterone did not influence the hormonal, liver or lipid profiles evaluated. Only three (6%) women suffered from mild vaginal irritation. Natural progesterone given as a vaginal tablet is well tolerated, safe and an easily administered treatment. Even in a non-oestrogenized vagina the absorption was efficient and the 100 mg dosage resulted in adequate serum progesterone concentrations.