Capreomycin was incorporated into multilamellar vesicles of pure dipalmitoylphosphatidylcholine. The pharmacokinetics and nephrotoxicity of capreomycin in the free and liposomal forms were studied in normal mice. The efficacies of the two forms were evaluated by using the Mycobacterium avium complex beige mouse model. Approximately 10(7) viable M. avium cells were injected intravenously. Seven days later, treatment with either liposomal or free capreomycin at 60 or 120 mg/kg of body weight was administered daily for 5 days. Mice were sacrificed 5 days after the end of treatment, and the viable bacteria in liver, spleen, lungs, and blood were counted. After 5 days of treatment with dosages of 60 or 120 mg/kg/day, the level of blood urea nitrogen increased in the group treated with free capreomycin but not in the group treated with liposomal capreomycin. After intravenous injection of 120 mg/kg, liposomes enhanced the diffusion of capreomycin in the spleen, lungs, and kidneys and increased the half-life in serum. The 120-mg/kg dose of liposomal capreomycin significantly reduced the number of viable mycobacteria in the liver, spleen, and blood compared with those in the controls. Although these results are promising, further studies are needed to assess the efficacy of liposomal capreomycin for the treatment of M. avium complex infections.