Comparison of transdermal and oral sequential gestagen in combination with transdermal estradiol: effects on bleeding patterns and endometrial histology.

Objective: To assess prospectively the effect on bleeding patterns, transformation of the endometrium, and rate of endometrial hyperplasia of transdermal norethisterone acetate when administered sequentially in combination with transdermal estradiol (E2), and to compare it to a regimen using oral medroxyprogesterone acetate.

Methods: Two hundred eighteen women were randomized to receive either transdermal E2 0.05 mg/day for 14 days followed by transdermal E2 0.05 mg/day plus transdermal norethisterone acetate 0.25 mg/day for 14 days, or transdermal E2 0.05 mg/day for 25 days with the addition of oral medroxyprogesterone acetate 10 mg/day on days 16-25, followed by a 3-day treatment-free period. Treatment was planned for 13 cycles of 28 days. The subjects kept daily bleeding diaries, and endometrial biopsies were taken before and at the end of treatment.

Results: The mean duration of bleeding (regular) induced by the gestagen was 7.33 days in the transdermal gestagen-treated group, which was 1.54 days longer than in the oral gestagen-treated group (P = .0001). The mean cycle day of onset was 25.74. Bleeding was spotting or light in the transdermal group in 77% of the days in which bleeding occurred. When comparing the two groups, there were no differences in the overall mean cycle day of onset or in the intensity of gestagen-induced bleeding. Breakthrough (irregular) bleeding episodes occurred in 42% of the transdermal subjects, lasted a mean of 4.18 days, and were spotting or light in 87% of the days when they occurred. There were no differences between the treatment groups. There was only one case (1.3%) of confirmed simple hyperplasia and five cases of failure of gestagenic transformation of the endometrium in 77 women treated for a mean of 367 days with transdermal gestagen.

Conclusion: A transdermal system delivering a combination of E2 and norethisterone acetate for 14 days in sequence with E2 delivered transdermally for 14 days produced bleeding patterns that are clinically acceptable and comparable to those produced by oral medroxyprogesterone acetate given in sequence with E2 delivered transdermally for 25 days. The use of the combination system was not associated with a significant risk of endometrial hyperplasia.