Steady-state bioavailability of estradiol from two matrix transdermal delivery systems, Alora and Climara

The relative bioavailability of estradiol from two matrix transdermal delivery systems, Alora (0.05 mg/day when applied for 3-4 days) and Climara (0.05 mg/day when applied for 7 days), was evaluated in this two-period, randomized crossover study.

A total of 27 healthy, postmenopausal women completed this study. Each subject received four successive doses of Alora every 84 h (3.5 days) and two doses of Climara every 168 h (7 days) in a randomized sequence without a washout period. Serial serum samples were collected over a 7-day period during the second week of each treatment. Samples were analyzed for estradiol and estrone using a validated radioimmunoassay method. Pharmacokinetic analyses were conducted using baseline-corrected parameters.

Fluctuations in serum estradiol levels were 44% higher for Climara, as indicated by the ratio of Cmax/Cmin. Because the Cmin values for the two regimens were similar, the differences in fluctuation reflected the difference in their Cmax values (49.8 pg/ml for Alora, 67.7 pg/ml for Climara.) The estradiol AUC for Climara was 124% (95% CI 115.6-133.7) of the value for Alora.

Serum estradiol concentrations were maintained at a more constant level during twice-weekly application of Alora than during once-weekly application of Climara. Both regimens were generally well tolerated and no serious skin or other adverse effects were reported by the subjects. However, Alora exhibited better skin tolerability as indicated by a lower incidence of moderate skin erythema. In addition, there was less adhesive transfer to skin at the application site with Alora.