Rifampin

Rifampin, also known as rifampicin, is an antibiotic in the rifamycin class. It inhibits bacterial DNA-dependent RNA polymerase by binding to the beta subunit, blocking RNA synthesis. It is bactericidal for many intracellular organisms and is particularly important in treating infections caused by Mycobacterium tuberculosis complex. Resistance can develop rapidly when used alone.

Common medical uses include active tuberculosis therapy as a core first‑line agent in combination regimens with isoniazid, pyrazinamide, and ethambutol. Rifampin is also used for post‑exposure prophylaxis against Neisseria meningitidis and Haemophilus influenzae type b, and as part of multidrug regimens for some Staphylococcus aureus infections and leprosy.

Pharmacokinetics and interactions: rifampin is well absorbed orally and undergoes hepatic metabolism with biliary excretion. It is a potent inducer of hepatic enzymes (including CYP450) and can autoinduce its own metabolism. This leads to numerous drug interactions, reducing the effectiveness of anticoagulants, antiretrovirals, oral contraceptives, and many other agents. Caution is advised in liver disease.

Adverse effects and safety: potential hepatotoxicity, GI upset, rash, and hypersensitivity reactions can occur. A distinctive side effect is orange to red discoloration of urine, sweat, and tears. Other adverse effects include flu-like symptoms and, less commonly, neuropathy or phlebitis with IV use. Monitoring liver function is recommended in at-risk individuals.

Resistance and stewardship: resistance to rifampin emerges readily with monotherapy due to rpoB gene mutations; there is cross-resistance with rifabutin and rifapentine. Therefore, rifampin is used only in combination therapies as part of established regimens.