A woman on a combined OCP containing 30 mcg ethinyl estradiol and 150 mcg levonorgestrel requires rifampicin for latent TB treatment. The pharmacist warns of contraceptive failure. The recommended approach is:

• A Switch to a progestogen-only pill, which is unaffected by CYP induction
• B Use additional barrier contraception throughout rifampicin therapy and for 4 weeks after stopping ✓
• C Increase the ethinyl estradiol dose to 50 mcg, which compensates for rifampicin-induced metabolism
• D Use depot medroxyprogesterone injection, which is not susceptible to CYP450 induction

Explanation

Rifampicin is a potent CYP3A4 and P-glycoprotein inducer that dramatically reduces plasma concentrations of both ethinyl estradiol and progestins in combined and progestogen-only pills, leading to contraceptive failure. Current FSRH and WHO MEC guidelines recommend using additional barrier contraception throughout rifampicin therapy and for 4 weeks after its completion, regardless of OCP type (including POPs, which are equally affected). Depot medroxyprogesterone acetate injection is also potentially affected by CYP induction and is not recommended as a reliable alternative during rifampicin therapy.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.