A 28-year-old with BMI 38 kg/m² and PCOS is counselled about combined oral contraceptive pills (COCPs) for cycle regulation. The primary concern regarding efficacy in this context relates to which pharmacokinetic principle?
- A Increased first-pass hepatic metabolism of ethinyl estradiol in obese women
- B Reduced gut absorption of progestin due to gastroparesis in obese women
- C Upregulation of sex hormone binding globulin in obese women reduces free ethinyl estradiol
- D Increased volume of distribution of ethinyl estradiol in adipose tissue, leading to reduced peak serum concentrations ✓
Explanation
The primary pharmacokinetic concern with COCPs in obese women is the increased volume of distribution of lipophilic ethinyl estradiol (and progestins) in adipose tissue, which reduces peak serum concentrations and potentially contraceptive efficacy. Epidemiological data (EUROGEST, MEGA study) show that combined OCP failure rates and VTE risk are higher in obese women. First-pass hepatic metabolism is not substantially increased in obesity for ethinyl estradiol. SHBG is typically reduced (not increased) in obese/hyperandrogenic women, actually increasing free steroid concentrations — working in the opposite direction.
Reference: Shaw's Textbook of Gynaecology, 17th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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