Plasma levels of progesterone after vaginal, rectal, or intramuscular administration of progesterone.
Plasma levels of progesterone were determined after vaginal, rectal, or im administration of 10-100 mg of progesterone to 35 female volunteers. Progesterone was assayed by a competitive protein-binding technique. The absorption was very rapid by all 3 routes of administration, usually resulting in peak plasma levels of progesterone within the first 8 hours after administration. The plasma levels remained elevated for longer periods of time than would be expected from the rapid rate of disappearence described for progesterone. Plasma levels corresponding to those encountered during the luteal phase of the menstrual cycle were attained with an im injection of 25 mg of progesterone in oil while an im dose of 100 mg resulted in a mean peak level corresponding to mid-pregnancy plasma levels of progesterone. However, there was considerable individual variation. The vaginal or rectal administration of 100 mg of progesterone in suppository form resulted in plasma levels in the range usually encountered during the luteal phase of the menstrual cycle. This means that with the vaginal or rectal administration of progesterone, about 4 times the im does is required to reach corresponding plasma levels. The authors recommend that to ensure physiologic luteal phase levels of progesterone in plasma, a daily im dose of 25 mg of progesterone in oil or 4 times this dose by vaginal or rectal administration is needed. When daily administration is utilized, a certain cumulative effect will be obtained. The total daily vaginal or rectal dose should be divided into 2 doses to obtain a stable elevated plasma level of progesterone.