Rifampin is an antibacterial agent active against many gram-positive cocci, Mycobacteria, Clostridium difficle, and select gram-negative organisms, namely Neisseria meningitides, N. gonorrhoeae, and Hemophilus influenzae. Clinically, rifampin is recommended for infections where the disease-causing organisms are identified, their drug susceptibility determined, and it is used in combination with other antimicrobial agents to prevent the drug resistance. It is used for the treatment of active/latent tuberculosis (TB), leprosy, and severe gram-positive bacterial infections like osteomyelitis, endocarditis, brain abscess, meningitis, and implant infections in combinations with other antimicrobial agents. Prophylactically, it is used for the prevention of TB, Meningococcal infections in high-risk groups like close contacts, history of travel to endemic areas, and Hemophilus influenzae carriers who can transmit the infection to children less than four years. It is also beneficial as a second-line agent for the treatment of cholestatic pruritis.[1][2][3]

Rifampin produces the antimicrobial activity by inhibition of DNA dependent RNA polymerase (RNAP) either by sterically blocking the path of the elongating RNA at the 5′ end or by decreasing the affinity of the RNAP for short RNA transcripts.[4][5][6] It specifically inhibits the microbial RNAP and has no action on the mammalian enzyme, thereby decreasing the number of adverse effects it can cause in humans.

Elevated levels of bile acids are primarily responsible for the pruritis seen with cholestatic diseases like primary biliary cirrhosis. Its antipruritic effect in these cholestatic disorders is by the upregulation of microsomal enzymes CYP3A, which in turn induces hydroxylation of bile acids. The hydroxylation of bile acids makes them incapable of inducing pruritis or decreases their ileal reabsorption or both, thus alleviating the pruritic symptoms.[7][8] 

Rifampin is a highly lipid-soluble drug and is available in oral or intravenous formulations. When given orally, it is rapidly absorbed and distributed throughout the body. It is excreted equally in bile and urine and has a half-life of 2.5 hours.[9] When meninges are inflamed, a significant amount of drug can enter the cerebrospinal fluid, thereby making it useful clinically in the treatment of bacterial meningitis.[10] It is available for intravenous use in critically ill patients with life-threatening infections caused by gram-positive organisms when oral formulations are not as effective.

It does not require dosage adjustments in renal disorders, but it is required in patients with preexisting liver diseases since rifampin is associated with significant hepatotoxicity. It can be safely administered during pregnancy and breastfeeding and is not associated with any congenital malformations or neonatal complications.[11][12] 

Rifampin is generally a well-tolerated drug but is associated with both dose-dependent and dose-independent adverse effects. Dose-dependent side effects include orange discoloration of body fluids like tears (can stain the contact lenses), sweat, saliva, urine, and also feces due to its excretion in them and gastrointestinal symptoms like nausea, anorexia, and diarrhea. If it causes diarrhea, testing for Clostridium difficile infection is indicated to rule out antibiotic-induced pseudomembranous colitis. Hepatotoxicity is also a well-documented side effect, especially in those with preexisting liver disease. Dose-independent adverse effects include hypersensitive reactions like urticaria, flu-like symptoms, thrombocytopenia, hemolysis, and renal failure. These hypersensitivity reactions are common when used intermittently or for a prolonged duration. They generally resolve with the discontinuation of rifampin.[13][14]

Any previous history of allergy to rifampin or other rifamycin's (rifabutin/ rifaximin/ rifapentine) is a significant contraindication to its use. It is also a potent inducer of many drug-metabolizing enzymes, notably cytochrome P450 (CYP) 3A4 and drug transporter proteins, such as hepatic P-glycoprotein. This property of rifampin reduces the efficacy of concomitantly administered drugs and thus can limit its administration. Commonly involved drugs include HIV protease inhibitors, antimycotics (itraconazole and ketoconazole), cyclosporine (can cause graft rejections), DHP CCB's, sulfonylureas, oral contraceptives, and warfarin. After starting rifampin, it takes around a week to induce drug-metabolizing enzymes and produce clinically significant interactions. Furthermore, it takes almost two weeks for this effect to wear-off after stopping rifampin.[15]