Rifampicin is a potent enzyme inducer. Which of the following drug interactions is MOST clinically critical in TB/HIV co-infection?
- A Rifampicin induces CYP2D6, reducing metoprolol plasma levels
- B Rifampicin competes with efavirenz for CYP2B6 metabolism
- C Rifampicin induces CYP3A4 and P-glycoprotein, dramatically reducing protease inhibitor and NNRTI plasma levels ✓
- D Rifampicin inhibits UGT1A1, increasing dolutegravir exposure
Correct answer: C. Rifampicin induces CYP3A4 and P-glycoprotein, dramatically reducing protease inhibitor and NNRTI plasma levels
Explanation
Rifampicin is one of the most potent inducers of CYP3A4 and P-glycoprotein, reducing plasma levels of virtually all HIV protease inhibitors (boosted or otherwise) by 75–90%, rendering them ineffective; it also substantially reduces NNRTI levels (e.g., nevirapine). For TB/HIV co-infection, rifabutin (a weaker CYP inducer) replaces rifampicin when protease inhibitors are needed, or efavirenz-based regimens are used with rifampicin at adjusted efavirenz doses since EFV is also induced but remains above therapeutic threshold.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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