From the Guidelines
The half-life of topical bioidentical estradiol concentrations is not explicitly stated in the provided evidence, but based on the context of transdermal administration, it can be inferred that the half-life is likely to be around 12-24 hours, similar to other transdermal estradiol formulations 1.
Key Points to Consider
- Transdermal administration of 17β-estradiol is preferred due to its ability to mimic physiological serum estradiol concentrations, providing a better safety profile than oral formulations 1.
- This route of administration avoids the hepatic first pass effect and minimizes the impact of estrogens on the synthesis of hemostatic factors 1.
- Transdermal 17βE has a more beneficial profile on circulating lipids, markers of inflammation, and blood pressure compared to oral formulations 1.
- The dosing of transdermal 17βE can range from 50-100 micrograms daily, as mentioned in the context of estrogen replacement therapy 1.
Clinical Implications
- The use of topical bioidentical estradiol formulations, such as gels or sprays, may require daily application to maintain therapeutic hormone levels, considering the relatively short half-life of estradiol.
- Application to clean, dry skin areas, avoiding the breasts, is recommended for optimal absorption and minimal side effects.
- The choice of transdermal estradiol over oral formulations may be preferred in certain clinical scenarios due to its safer profile and more stable estrogen levels, as supported by the evidence 1.
From the Research
Half-Life of Topical Bioidentical Estradiol Concentrations
- The half-life of estradiol after removal of a transdermal estradiol patch was found to be 161 minutes (range 107-221 minutes) in a study of 8 healthy postmenopausal women 2.
- The study also found a direct relationship between the subjects' weight and the half-life of estradiol (r = 0.79, p = 0.02) 2.
- Another study found that the terminal half-lives for different estrogen compounds vary from 1-12 hours after oral or intravenous administration 3.
- A study on bioidentical compounded hormones found that the pharmacokinetics of these preparations are not well understood, and further studies are needed to determine comparable doses to conventional hormonal preparations 4.
- The half-life of topical bioidentical estradiol concentrations is not directly stated in the provided studies, but it can be inferred that the half-life of estradiol after transdermal administration is around 2.7 hours or 161 minutes 2.
Factors Affecting Half-Life
- Weight: a study found a direct relationship between the subjects' weight and the half-life of estradiol (r = 0.79, p = 0.02) 2.
- Administration route: transdermal administration bypasses the first-pass effect, which can affect the half-life of estradiol 3.
- Dosing: a study found that different doses of compounded bioidentical estradiol cream resulted in lower levels of estrogen compared to a standard-dose estradiol patch 4.