A 28-year-old woman taking combined OCP (ethinyl estradiol + levonorgestrel) develops a DVT. The prothrombotic mechanism of ethinyl estradiol involves:

• A Platelet activation through direct estrogen receptor signaling increasing TXA2 generation
• B Inhibition of tissue plasminogen activator (tPA) production in endothelial cells decreasing fibrinolysis
• C Upregulation of PAI-1 (plasminogen activator inhibitor-1) in the liver decreasing fibrinolytic capacity
• D Hepatic upregulation of factors II, VII, X and fibrinogen synthesis along with reduced protein S and antithrombin levels mediated by estrogen receptor-alpha in hepatocytes ✓

Explanation

Ethinyl estradiol acts on hepatic estrogen receptor-alpha to increase synthesis of procoagulant proteins (factors II, VII, VIII, X, XII, and fibrinogen) and simultaneously reduce anticoagulant proteins (protein S, antithrombin, protein C). The net shift toward a procoagulant state, particularly the increase in factor VII and decrease in protein S, is the primary mechanism of OCP-associated VTE risk. This effect is dose-dependent; modern low-dose OCPs (20mcg EE) carry lower risk than earlier 50mcg formulations. The progestogen component (especially third-generation progestogens with androgenic activity) also modestly influences this coagulation balance.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.