Significant differences in estradiol bioavailability from two similarly labelled estradiol matrix transdermal systems

Area of Science:

• Endocrinology
• Pharmacokinetics
• Drug Delivery Systems

Background:

• Transdermal estradiol systems are used for hormone replacement therapy.
• Understanding the bioavailability differences between systems is crucial for effective treatment.

Purpose of the Study:

• To compare the bioavailability of estradiol from two transdermal systems, Alora and Evorel.
• To assess the consistency of estradiol delivery over an 84-hour interval.

Main Methods:

• A randomized, two-period cross-over study involving 33 postmenopausal women.
• Subjects applied Alora or Evorel patches (delivering 50 µg/day 17β-estradiol) sequentially.
• Serum estradiol levels were measured via radioimmunoassay over 84 hours.

Main Results:

• Evorel exhibited a significantly higher fluctuation index (135%) compared to Alora (76%).
• Alora showed a significantly higher baseline-corrected area under the curve (2871.8 pg h/ml) than Evorel (1870.6 pg h/ml).
• Both systems were generally well tolerated.

Conclusions:

• Alora provides a higher and more consistent systemic concentration of estradiol over the dosing interval compared to Evorel.
• Significant differences in estradiol delivery exist between Alora and Evorel, despite identical nominal delivery rates.
• Further research is needed to determine the full clinical significance of these delivery differences.