A woman on combined oral contraceptive pills containing ethinyl estradiol develops a deep vein thrombosis. The most specific pharmacodynamic mechanism linking ethinyl estradiol to venous thromboembolism is:

• A Ethinyl estradiol directly activates platelet thromboxane synthesis, increasing platelet aggregation
• B Ethinyl estradiol upregulates PAI-1 (plasminogen activator inhibitor-1) in adipose tissue, inhibiting fibrinolysis
• C Ethinyl estradiol competitively inhibits vitamin K at VKORC1, creating a paradoxical hypercoagulable state at low doses
• D Ethinyl estradiol increases hepatic synthesis of coagulation factors II, VII, X and fibrinogen via estrogen response elements on their promoters, and reduces protein S and antithrombin levels ✓

Explanation

Ethinyl estradiol (EE) stimulates hepatic synthesis of procoagulant factors II, VII, VIII, X, fibrinogen, and von Willebrand factor via nuclear estrogen receptor-mediated gene transcription. Simultaneously, EE reduces anticoagulant proteins S and antithrombin levels. This net shift toward a procoagulant state accounts for the 3–4× increased VTE risk with combined OCPs. Third-generation progestogens (desogestrel, gestodene) potentiate EE's procoagulant effect compared to levonorgestrel, partly through antifibrinolytic effects. The prothrombotic effect is independent of platelet aggregation or VKORC1 inhibition.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.