Oral Estradiol Equivalent of 0.1 mg Biweekly Transdermal Patch
A 0.1 mg (100 mcg/day) transdermal estradiol patch applied twice weekly is approximately equivalent to 2 mg of oral micronized estradiol daily. 1, 2
Dose Equivalency Rationale
The conversion is based on the following pharmacokinetic principles:
Transdermal estradiol bypasses first-pass hepatic metabolism, delivering physiologic 17β-estradiol directly into systemic circulation at a constant rate, whereas oral estradiol undergoes extensive hepatic conversion to estrone before reaching systemic circulation 3, 4
20 mcg of ethinyl estradiol (EE) is approximately equivalent to 2 mg of oral 17β-estradiol valerate, and transdermal 100 mcg/day patches achieve similar therapeutic efficacy to 2 mg oral estradiol in controlling menopausal symptoms 1
Serum estradiol levels with 2 mg oral estradiol average 107.6 pg/mL, which falls within the therapeutic range achieved by 100 mcg/day transdermal patches (typically 35-100 pg/mL for symptom control) 5, 4
Standard Dosing Context
The 100 mcg/day (0.1 mg) transdermal patch represents the standard adult maintenance dose for hormone replacement therapy in postmenopausal women and those with premature ovarian insufficiency 2, 6
Initial therapy typically starts at 50 mcg/day patches applied twice weekly, with titration to 100 mcg/day if symptoms persist after 2-3 months 2
Maximum maintenance dosing reaches 100-200 mcg/day transdermal (equivalent to 2-4 mg oral estradiol daily) for optimal symptom control 1, 2
Critical Endometrial Protection Requirement
Women with an intact uterus must receive progestin supplementation when taking either transdermal or oral estradiol to prevent endometrial hyperplasia and cancer:
Add 100-200 mg oral micronized progesterone daily for 12-14 days every 28 days (sequential regimen) 1, 2, 6
Alternative progestins include 10 mg medroxyprogesterone acetate or 5-10 mg dydrogesterone for 12-14 days monthly 1
Never omit progestin in women with a uterus, as unopposed estrogen significantly increases endometrial cancer risk 7
Important Clinical Caveats
Transdermal delivery is strongly preferred over oral estradiol for the following reasons:
Transdermal estradiol has a neutral effect on venous thromboembolism risk (OR 0.9), whereas oral estradiol increases VTE risk significantly (OR 4.2) 1
Transdermal administration avoids adverse hepatic effects including increased SHBG, renin substrate, and coagulation factors that occur with oral estrogen 1, 3
Blood pressure and metabolic profiles are more favorable with transdermal versus oral estradiol, particularly in young women with premature ovarian insufficiency 1
If switching from transdermal to oral formulation is necessary, start with 2 mg oral micronized estradiol (not ethinyl estradiol) and monitor for increased thrombotic risk, particularly in patients with additional VTE risk factors 1, 7