Drug Groups

approved

Description

A broad-spectrum antibiotic that is being used as prophylaxis against disseminated Mycobacterium avium complex infection in HIV-positive patients. [PubChem]

Indication

For the prevention of disseminated Mycobacterium avium complex (MAC) disease in patients with advanced HIV infection.

Pharmacology

Rifabutin is an antibiotic that inhibits DNA-dependent RNA polymerase activity in susceptible cells. Specifically, it interacts with bacterial RNA polymerase but does not inhibit the mammalian enzyme. It is bactericidal and has a very broad spectrum of activity against most gram-positive and gram-negative organisms (including Pseudomonas aeruginosa) and specifically Mycobacterium tuberculosis. Because of rapid emergence of resistant bacteria, use is restricted to treatment of mycobacterial infections and a few other indications. Rifabutin is well absorbed when taken orally and is distributed widely in body tissues and fluids, including the CSF. It is metabolized in the liver and eliminated in bile and, to a much lesser extent, in urine, but dose adjustments are unnecessary with renal insufficiency.

Toxicity

LD₅₀ = 4.8 g/kg (mouse, male)

Affected Organisms

Biotransformation

Hepatic. Of the five metabolites that have been identified, 25-O-desacetyl and 31-hydroxy are the most predominant. The former metabolite has an activity equal to the parent drug and contributes up to 10% to the total antimicrobial activity.

Absorption

Rifabutin is readily absorbed from the gastrointestinal tract, with an absolute bioavailability averaging 20%.

Half Life

45 (± 17) hours

Protein Binding

85%

Elimination

A mass-balance study in three healthy adult volunteers with 14C-labeled rifabutin showed that 53% of the oral dose was excreted in the urine, primarily as metabolites. About 30% of the dose is excreted in the feces.

Clearance

* 0.69 +/- 0.32 L/hr/kg

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