Absorption and bioavailability of oestradiol from a gel, a patch and a tablet

Area of Science:

• Endocrinology
• Pharmacokinetics
• Women's Health

Background:

• Hormone replacement therapy (HRT) is crucial for managing menopausal symptoms.
• Different estradiol formulations (oral, transdermal gel, transdermal patch) offer varied pharmacokinetic profiles.
• Understanding bioavailability and serum concentrations is key for effective HRT.

Purpose of the Study:

• To compare serum estradiol and estrone concentrations and bioavailability.
• To evaluate single-dose and steady-state pharmacokinetics of oral estradiol valerate, transdermal estradiol gel, and transdermal estradiol patch.
• To assess bioequivalence between different estradiol delivery methods.

Main Methods:

• Two open-label, randomized, cross-over studies in postmenopausal women.
• Administration of oral estradiol valerate (2 mg/day), transdermal estradiol gel (1.5 mg/day), and transdermal estradiol patch (50 µg/24h).
• Serum hormone levels measured via RIA at various time points post-administration.

Main Results:

• Oral tablets and transdermal gel showed similar serum estradiol profiles with rapid peak concentrations.
• Transdermal patch provided more stable levels but with greater fluctuation between peak and trough concentrations.
• Estradiol bioavailability was higher from the tablet compared to the gel; the gel was not bioequivalent to either the tablet or the patch.

Conclusions:

• Oral estradiol valerate demonstrated significantly higher bioavailability than transdermal gel.
• Observed differences in serum estradiol profiles and lack of bioequivalence necessitate careful consideration.
• Individual dose adjustments are recommended when transitioning between oral and transdermal estradiol formulations.