Bioavailability of progesterone with different modes of administration

The bioavailability of micronized progesterone (P) was studied by measuring sequential serum P concentrations after a single bolus of 50-200 mg P given sublingually, orally (capsule and tablet), vaginally and rectally (suppositories) during the follicular phase in a group of normally menstruating women. When compared to other modes of P administration, the area under the curve during the first eight hours was twice as high with the rectal route. With 50 and 100 mg P given sublingually and 100 and 200 mg ingested as tablets, peak levels and area under the curve were twice as high with the higher dosage. The response was more sustained with the higher dosage. All subjects exhibited a significant increase in serum P levels over baseline that persisted for at least eight hours. P levels were still increased over baseline at 24 hours in all subjects after the administration of 100-mg vaginal and rectal suppositories and 200-mg tablets. These findings are in general agreement with previous reports showing that luteal phase serum P concentrations can be reached easily with non-parenteral modes of administering micronized P and that oral P administration could become an attractive alternative to the currently used oral mode of administering synthetic progestins.