We examined various pharmacokinetic parameters of progesterone (P) after its administration in a vaginal suppository to healthy females and compared these parameters with those after injection of P at different sites, in order to evaluate the effectiveness of the P vaginal suppository. The increase in the blood P concentration after administering it in the vaginal suppository was similar to that for injecting P (25 mg) into the gluteal region. Since the P vaginal suppository is a useful P preparation and can be readily used, it can be the dosage form of first choice in P replacement therapy. In addition, since our basic experiment suggested that there was a circadian rhythm in the blood P concentration, it may be possible to determine the optimum administration time for maintaining the blood P concentration based on this rhythm.
