Rifampin is a derivative of rifamycin that suppresses RNA synthesis, resulting in broad antimicrobial properties. When rifampin is used as monotherapy, resistance develops rapidly because of single-point mutations. In combination therapy, rifampin has many important applications. It exhibits good activity against many gram-positive cocci (including methicillin-resistant Staphylococcus aureus), some gram-negative organisms, Legionella, many mycobacteria and some fungi.
Loeffler described the utility of rifampin in nontuberculosis infections. Rifampin is used at dosages of 10 to 20 mg per kg per day (intravenous or oral), with a maximal dosage of 600 mg per day. In pediatric suspensions it can be formulated in doses of 15 or 50 mg per mL in simple syrup and is commercially available in 150- or 300-mg breakable capsules. Rifampin may discolor the tears, urine and feces. Hepatic enzyme induction may result in decreased levels of other medications (i.e., coumadin, oral contraceptives, clarithromycin, azoles) that are metabolized by the same pathway. Rifabutin (another rifamycin) exhibits less hepatic enzyme induction and less effect on other drug levels. Other side effects include gastrointestinal upset, rash, hepatotoxicity, hypersensitivity and a flu-like syndrome. The parenteral form may cause thrombophlebitis.
As monotherapy, rifampin is used to clear pharyngeal carriage of Haemophilus influenzae type B and Neisseria meningitidis, primarily as prophylactic therapy in persons who are in close contact with active carriers. It is also used as monotherapy to eradicate pharyngeal carriage of group B streptococci in infants who have recurrent group B streptococcal sepsis, and in combination therapy to clear resistant Streptococcus pneumoniae colonization or nasal carriage of S. aureus in patients with recurrent furunculosis.
Although not every case of cat scratch disease (Bartonella henselae) requires treatment, rifampin may be useful in combination regimens to treat patients with complicated or severe cases. Resistant S. pneumoniae can be treated with a combination of a third-generation cephalosporin and rifampin. In the treatment of nontuberculous mycobacteria (e.g., Mycobacterium aviumintracellulare complex that occurs in immunocompromised hosts), rifampin may be used with clarithromycin, azithromycin and, sometimes, ethambutal.
The author concludes that rifampin has limited use as monotherapy because of the rapid development of resistance but is useful in combination therapy for many serious infections.