Rifamycins

Oral absorption is good, producing wide distribution in body tissues and fluids, including cerebrospinal fluid.

Rifampin is concentrated in polymorphonuclear granulocytes and macrophages, facilitating clearance of bacteria from abscesses. It is metabolized in the liver and eliminated in bile and, to a much lesser extent, in urine.

Rifampin is active against

• Most gram-positive and some gram-negative bacteria

• Mycobacterium species

Resistance develops rapidly, so rifampinis rarely used alone. Rifampin is used with other antibiotics for

• Tuberculosis

• Atypical mycobacterial infection (rifampin is active against many nontuberculous mycobacteria, but rapidly growing mycobacteria, such as Mycobacterium fortuitum, M. chelonae, or M. abscessus, are naturally resistant)

• Leprosy(with dapsone with or without clofazimine)

• Staphylococcal infections, including osteomyelitis, prosthetic valve endocarditis, and infections involving foreign bodies such as a prosthetic joint (with other antistaphylococcal antibiotics)

• Legionellainfections (older data suggest better outcomes for rifampin when used witherythromycin; use of rifampinwith azithromycin or a fluoroquinolone offers no advantage)

• Pneumococcal meningitis when organisms are susceptible to rifampin(with vancomycin with or without ceftriaxone or cefotaxime forceftriaxone- or cefotaxime-resistant organisms [minimum inhibitory concentration > 4 mcg/mL]) or when expected clinical or microbiologic response is delayed

Rifampin can be used alone for prophylaxis of close contacts of patients with meningococcal meningitis or Haemophilus influenzae type b meningitis.

Rifabutin andrifampin are equally efficacious in regimens for tuberculosis in patients who are HIV-positive and HIV-negative. However, if patients are receiving antiretroviral therapy (ART), rifabutin is preferred because it is less likely to induce cytochrome P-450 metabolic enzymes that lower serum levels of protease inhibitors and non-nucleoside reverse transcriptase inhibitors.

Rifampin is preferred overrifabutin for Mycobacterium avium complex (MAC) lung disease, unless patients are receiving ART; in such cases, rifabutin may be substituted. However, rifabutin is preferred over rifampin for disseminated MAC infections because of its superior activity in vitro and reduced drug interaction potential.

Rifapentine is used to treat pulmonary and latent tuberculosis.

Rifampin and rifabutin are contraindicated in patients who have had an allergic reaction to them.

Some animal reproduction studies with rifabutin showed adverse effects when drug levels were higher than those typically achieved in humans. No adequate and well-controlled studies have been done in pregnant or breastfeeding women. Safety during breastfeeding is unknown.

Animal reproduction studies with rifampin or rifapentine show some risk (ie, teratogenicity) at medication levels less than or equal to those typically achieved in humans. No adequate and well-controlled studies with either medication have been done in pregnant women.

Because of potential tumorigenicity shown in animal studies, the manufacturer does not recommend use of rifampin during breastfeeding. However, the Centers for Disease Control and Prevention (CDC) does not consider rifampin a contraindication to breastfeeding; a decision to stop breastfeeding or to stop the medication should be made depending on the importance of the medication to the mother.

Adverse effects of rifamycins include

• Hepatitis (most serious)

• Gastrointestinal disturbances

• Central nervous system effects

• Myelosuppression

Hepatitis occurs much more often when isoniazid or pyrazinamide is used concurrently with rifampin. During the first week of therapy,rifampin may cause a transient rise in unconjugated serum bilirubin, which results from competition between rifampin and bilirubin for excretion and which is not in itself an indication for interrupting treatment.

Central nervous system effects may include headache, drowsiness, ataxia, and confusion. Rash, fever, leukopenia, hemolytic anemia, thrombocytopenia, interstitial nephritis, acute tubular necrosis, renal insufficiency, and interstitial nephritis are generally considered to be hypersensitivity reactions and occur when therapy is intermittent or when treatment is resumed after interruption of a daily dosage regimen; they are reversed when rifampin is stopped.

Rifabutin can cause dose-dependent unilateral or bilateral uveitis.

Less serious adverse effects are common; they include heartburn, nausea, vomiting, and diarrhea. Rifampin, rifabutin, and rifapentine can cause temporary reddish orange discoloration of urine, saliva, sweat, sputum, and tears. Soft contact lenses may be permanently discolored.

If patients have a liver disorder, liver tests should be done before rifampin therapy is started and every 2 to 4 weeks during therapy, or an alternate medication should be used. Dose adjustments are unnecessary for renal insufficiency.

Rifampin interacts with many medications because it is a potent inducer of hepatic cytochrome P-450 (CYP450) microsomal enzymes.Rifampinaccelerates elimination and thereby may decrease the effectiveness of the following medications: angiotensin-converting enzyme inhibitors, atovaquone, barbiturates, beta-blockers, calcium channel blockers,chloramphenicol, clarithromycin, oral and systemic hormone contraceptives, corticosteroids, cyclosporine, dapsone, digoxin, doxycycline, fluconazole, haloperidol, itraconazole, ketoconazole, the non-nucleoside reverse transcriptase inhibitors delavirdine and nevirapine, opioid analgesics, phenytoin, protease inhibitors, quinidine, sulfonylureas, tacrolimus, theophylline, thyroxine, tocainide, tricyclic antidepressants, voriconazole, warfarin, and zidovudine. To maintain optimum therapeutic effect of these medications, clinicians may have to adjust the dosage when rifampin is started or stopped.

Conversely, protease inhibitors, as well as other medications (eg, azoles, the macrolide clarithromycin, non-nucleoside reverse transcriptase inhibitors) inhibit CYP450 enzymes and increase levels of rifamycins and thus potentially increase the frequency of toxic reactions. For example, uveitis occurs more commonly when rifabutin is used with clarithromycin or azoles.