Objective: To study the pharmacokinetics of the transvaginal absorption of 100 mg micronized P from an oil-based solution in postmenopausal women before and after the estrogenization of the vaginal mucosa and to evaluate the endometrial effects of 10 days of once daily P vaginal administration.
Design: Prospective clinical trial.
Setting: University Medical School.
Patients: Nine postmenopausal women undergoing hormone replacement therapy.
Interventions: A micronized P (100 mg) oil-based solution currently available on the market for IM use was administered vaginally by means of a Teflon cannula without the aid of a speculum. Subsequently, the women received 4 weeks 0.1 mg/d transdermal E2 treatment combined on the last 10 days with the once daily vaginal administration of P in the same way as before.
Main outcome measures: At the first (before estrogen) and second (during estrogen therapy) P administrations, P serum levels were measured at time 0, and then after 15, 30, 45, 60, 120, 240, 480, and 1440 minutes. Endometrial samples were collected at the end of treatment.
Results: After the first administration, a mean Cmax of 5.40 +/- 0.92 ng/mL (mean +/- SD) was reached at a Tmax of 45 minutes (range 30 to 480 minutes). The serum concentrations returned to their initial values after 24 hours. The second P administration reached a mean Cmax of 5.30 +/- 1.04 ng/mL at a Tmax of 60 minutes (range 30 to 240 minutes); after 24 hours, the serum P levels still were significantly higher than at baseline and at the same time after the first administration. None of the women complained of significant vaginal losses. No signs of vaginal phlogosis or irritation were observed. In all subjects, histologic evaluation showed clear endometrial secretory changes.
Conclusions: The daily vaginal administration of one vial of micronized P for 10 days allowed useful serum P levels to be reached, especially after estrogen therapy, and induced clear secretory changes in the endometrium.