Bioavailability of estradiol from two transdermal patches

Area of Science:

• Pharmacokinetics and Drug Delivery
• Endocrinology
• Dermatology

Background:

• Estradiol (E2) transdermal patches are crucial for hormone replacement therapy in postmenopausal women.
• Different patch designs, such as matrix and liquid-reservoir types, influence drug release and absorption kinetics.
• Understanding bioavailability differences is key to optimizing therapeutic efficacy and patient compliance.

Purpose of the Study:

• To compare the bioavailability of estradiol from a novel "matrix type" transdermal patch (Test patch) against a "liquid-reservoir" transdermal patch (Reference patch).
• To evaluate both the extent and rate of estradiol absorption over a 4-day application period.

Main Methods:

• A two-way randomized cross-over study involving 28 healthy postmenopausal women.
• Application of two patch types (Test and Reference) with identical total estradiol content and nominal release rates.
• Serum estradiol concentrations were monitored over 96 hours to determine pharmacokinetic parameters, including AUC0-96h and Cmax.

Main Results:

• The extent of estradiol bioavailability (AUC0-96h) was comparable between the Test and Reference patches.
• Significant differences were observed in the rate of bioavailability: the Reference patch exhibited rapid initial release followed by a marked decline, potentially dropping below effective levels.
• The Test patch demonstrated a more constant release and absorption rate, maintaining sustained estradiol concentrations with smaller fluctuations over the 4-day period.

Conclusions:

• The Test patch is bioequivalent to the Reference patch in terms of the extent of estradiol absorption.
• The Test patch offers an advantage in the rate of absorption, providing more consistent serum estradiol levels compared to the Reference patch.
• This suggests the Test patch may offer improved therapeutic stability for estradiol delivery in postmenopausal hormone therapy.