Identification of (+)-erythro-mefloquine as an active enantiomer with greater efficacy than mefloquine against Mycobacterium avium infection in mice

Infection caused by Mycobacterium avium is common in AIDS patients who do not receive treatment with highly active antiretroviral therapy (HAART) or who develop resistance to anti-HIV therapy. Mefloquine, a racemic mixture used for malaria prophylaxis and treatment, is bactericidal against M. avium in mice. MICs of (+)-erythro-, (-)-erythro-, (+)-threo-, and (-)-threo-mefloquine were 32 μg/ml, 32 μg/ml, 64 μg/ml, and 64 μg/ml, respectively. The postantibiotic effect for (+)-erythro-mefloquine was 36 h (MIC) and 41 h for a concentration of 4× MIC. The mefloquine postantibiotic effect was 25 h (MIC and 4× MIC). After baseline infection was established (7 days), the (+)- and (-)-isomers of the diastereomeric threo- and erythro-α-(2-piperidyl)-2,8-bis(trifluoromethyl)-4-quinolinemethanol were individually used to orally treat C57BL/6 bg(+)/bg(+) beige mice that were infected intravenously with M. avium. Mice were also treated with commercial mefloquine and diluent as controls. After 4 weeks of treatment, the mice were harvested, and the number of bacteria in spleen and liver was determined. Mice receiving (+)- or (-)-threo-mefloquine or (-)-erythro-mefloquine had numbers of bacterial load in tissues similar to those of untreated control mice at 4 weeks. Commercial mefloquine had a bactericidal effect. However, mice given the (+)-erythro-enantiomer for 4 weeks had a significantly greater reduction of bacterial load than those given mefloquine. Thus, (+)-erythro-mefloquine is the active enantiomer of mefloquine against M. avium and perhaps other mycobacteria.