Rifampin induces hepatic enzymes, leading to interactions with which medications?

• A. It inhibits hepatic enzymes causing accumulation
• B. It induces hepatic enzymes, increasing interactions with oral contraceptives and antiretrovirals
• C. It has no effect on drug metabolism
• D. It reduces absorption of all oral medications

Answer: (B)

Rifampin is a strong inducer of hepatic drug-metabolizing enzymes, especially the cytochrome P450 system (notably CYP3A4). By boosting the activity of these enzymes, it speeds up the metabolism of drugs that are substrates for them, which lowers their blood levels and can reduce or negate therapeutic effects. This is why it interacts with medications like oral contraceptives, whose hormone levels can fall, increasing the risk of breakthrough bleeding or pregnancy, and with antiretrovirals, where reduced drug levels can lead to virologic failure and resistance. This induction of enzymes explains why the combination with these drugs is a key concern.