Rifampin - Drugs Used In Tuberculosis

RIFAMPIN

Rifampin is a semisynthetic derivative of rifamycin, an antibiotic produced by Streptomyces mediterranei. It is active in vitro against gram-positive and gram-negative cocci, some enteric bacteria, mycobacteria, and chlamydiae. Susceptible organisms are inhib-ited by less than 1 mcg/mL. Resistant mutants are present in all microbial populations at approximately 1 in 10⁶ organisms and are rapidly selected out if rifampin is used as a single drug, espe-cially in a patient with active infection. There is no cross-resistance to other classes of antimicrobial drugs, but there is cross-resistance to other rifamycin derivatives, eg, rifabutin and rifapentine.

Mechanism of Action, Resistance, & Pharmacokinetics

Rifampin binds to the β subunit of bacterial DNA-dependent RNA polymerase and thereby inhibits RNA synthesis. Resistance results from any one of several possible point mutations in rpoB, the gene for the β subunit of RNA polymerase. These mutations result in reduced binding of rifampin to RNA polymerase. Human RNA polymerase does not bind rifampin and is not inhibited by it. Rifampin is bactericidal for mycobacteria. It readily penetrates most tissues and penetrates into phagocytic cells. It can kill organisms that are poorly accessible to many other drugs, such as intracellular organisms and those sequestered in abscesses and lung cavities.

Rifampin is well absorbed after oral administration and excreted mainly through the liver into bile. It then undergoes enterohepatic recirculation, with the bulk excreted as a deacylated metabolite in feces and a small amount excreted in the urine. Dosage adjustment for renal or hepatic insufficiency is not necessary. Usual doses result in serum levels of 5–7 mcg/mL. Rifampin is distributed widely in body fluids and tissues. The drug is relatively highly protein-bound, and adequate cerebrospinal fluid concentrations are achieved only in the presence of meningeal inflammation.

Clinical Uses

A. Mycobacterial Infections

Rifampin, usually 600 mg/d (10 mg/kg/d) orally, must be adminis-tered with isoniazid or other antituberculous drugs to patients with active tuberculosis to prevent emergence of drug-resistant mycobac-teria. In some short-course therapies, 600 mg of rifampin is given twice weekly. Rifampin, 600 mg daily or twice weekly for 6 months, also is effective in combination with other agents in some atypical mycobacterial infections and in leprosy. Rifampin, 600 mg daily for 4 months as a single drug, is an alternative to isoniazid for patients with latent tuberculosis who are unable to take isoniazid or who have had exposure to a case of active tuberculosis caused by an iso-niazid-resistant, rifampin-susceptible strain.

B. Other Indications

Rifampin has other uses in bacterial infections. An oral dosage of 600 mg twice daily for 2 days can eliminate meningococcal car-riage. Rifampin, 20 mg/kg/d for 4 days, is used as prophylaxis in contacts of children with Haemophilus influenzae type b disease. Rifampin combined with a second agent is used to eradicate staphylococcal carriage. Rifampin combination therapy is also indicated for treatment of serious staphylococcal infections such as osteomyelitis and prosthetic valve endocarditis.

Adverse Reactions

Rifampin imparts a harmless orange color to urine, sweat, and tears (soft contact lenses may be permanently stained). Occasional adverse effects include rashes, thrombocytopenia, and nephritis. Rifampin may cause cholestatic jaundice and occasionally hepatitis, and it commonly causes light-chain proteinuria. If administered less often than twice weekly, rifampin may cause a flu-like syndrome characterized by fever, chills, myalgias, anemia, and thrombocytope-nia. Its use has been associated with acute tubular necrosis. Rifampin strongly induces most cytochrome P450 isoforms (1A2, 2C9, 2C19, 2D6, and 3A4), which increases the elimination of numer-ous other drugs including methadone, anticoagulants, cyclosporine, some anticonvulsants, protease inhibitors, some nonnucleoside reverse transcriptase inhibitors, contraceptives, and a host of others. Co-administration of rifampin results in significantly lower serum levels of these drugs.