Comparative study of progesterone plasma levels after nasal spray and intramuscular administration of natural progesterone in menopausal women.

11 mg natural progesterone (P) was administered to 20 healthy menopausal women by means of a nasal spray or intramuscular injection. Circulating P levels were calculated at various times after administration. The spray formulation yielded a CMax of 3.75 ng/ml at TMax = 60 min, the area under the curve (AUC)0-720 being 1,481.6 +/- 343. Intramuscular administration yielded a mean CMax of 4.137 ng/ml at TMax = 240 min, the AUC0-720 being 2,491.2 +/- 540. P absorption was faster through the nasal than through the intramuscular route, but intramuscular administration led to high serum levels for a much longer period.