Major
Rifampicin × ritonavir
Antituberculous antibiotic×HIV protease inhibitor / pharmacokinetic booster
Mechanism
Rifampicin strongly induces CYP3A4 – the main ritonavir metabolic route. Ritonavir plasma levels fall by 35%, reducing its ability to boost other antiretrovirals. Antiretroviral efficacy is lost.
Symptoms
The patient feels nothing. Laboratory: rising HIV viral load. Risk of antiretroviral resistance.
Management
Avoid the combination. Alternative anti-TB drug in HIV patients: rifabutin (weaker CYP3A4 induction). Alternative ritonavir-free regimens: dolutegravir + tenofovir + emtricitabine (no booster needed).
Check the full regimen, not just this pair
Opens the checker with these two drugs prefilled. Add the rest of the regimen and recompute additive risks.