Rifabutin (ansamycin LM 427): a new rifamycin-S derivative for the treatment of mycobacterial diseases.

Rifabutin (ansamycin LM 427), a semisynthetic spiropiperidyl derivative of rifamycin S, shows good in vitro activity against most mycobacterial species, including Mycobacterium avium complex. In animal models, the drug is more active against both Mycobacterium tuberculosis and Mycobacterium leprae than in rifampin, and studies indicate that rifabutin is active against some rifampin-resistant strains of both species. The drug has a long half-life (16 hr) in humans and a marked tissue tropism, with tissue levels five- to 10-fold higher than that in the serum. In animals rifabutin is no more toxic than rifampin. A large experience from the compassionate use of rifabutin for life-threatening mycobacterial infections in humans, most commonly disseminated M. avium complex disease in patients with AIDS, has also indicated relative drug safety. Although some data suggest that rifabutin is effective, firm conclusions about drug efficacy await results from controlled clinical trials.