Comparison of estrogenic components used for hormonal contraception

Area of Science:

• Endocrinology and Reproductive Health
• Pharmacology and Drug Development

Background:

• Combined oral contraceptives (COCs) traditionally use ethinyl estradiol (EE), a potent synthetic estrogen.
• Efforts to improve COC safety and tolerability involve using natural estrogens like estradiol (E2) or its prodrugs.
• A novel weak natural estrogen, estetrol (E4), is now available in a drospirenone-combined COC.

Purpose of the Study:

• To conduct a comparative analysis of ethinyl estradiol (EE), estradiol (E2), and estetrol (E4) in COCs.
• To evaluate structure-function relationships, receptor binding, potency, metabolism, pharmacokinetics, and pharmacodynamics.
• To assess the potential of E4 as a safer alternative to EE and E2 in oral contraception.

Main Methods:

• Comparative analysis of estrogen structure-function relationships.
• Assessment of estrogen receptor (ER) binding affinities (ERα and ERβ).
• Evaluation of potency, metabolism, pharmacokinetic parameters, and pharmacodynamics, including ovulation inhibition and effects on coagulation factors.

Main Results:

• Ethinyl estradiol (EE) exhibits higher binding affinity to ERα than E2, while E4 has lower affinity than E2.
• EE significantly increases hepatic globulins and coagulation factors; E2 and E4 may be less stimulatory.
• Estetrol (E4) demonstrates higher bioavailability and limited metabolites compared to EE and E2, requiring higher doses for ovulation inhibition.

Conclusions:

• Estetrol (E4) possesses distinct pharmacokinetic and pharmacodynamic properties compared to EE and E2.
• E4-based COCs may offer improved safety profiles due to lower estrogenic potency and potentially reduced impact on coagulation.
• While data on venous thromboembolism risk for E4-based COCs are limited, E4 shows promise as a novel contraceptive estrogen.