Inefficacy of metronidazole in experimental infections of Leishmania donovani, L. mexicana, and Trypanosoma brucei brucei.

Metronidazole has been claimed in several earlier reports to be active in human cases of leishmaniasis and trypanosomiasis. Its efficacy against the protozoa causing these diseases was tested in hamsters infected with Leishmania mexicana or L. donovani, and in mice infected with Trypanosoma brucei brucei. In separate experiments, hamsters were either inoculated intradermally into the nose with 5 million amastigotes of L. mexicana or intracardially with 10-30 million amastigotes of L. donovani, and mice were infected intraperitoneally with 30 million T. b. brucei. Metronidazole was administered in four oral doses on alternate days for a total of 375 mg/kg to hamsters and 500 mg/kg to mice. Sodium stibogluconate (Pentostam) served as a positive control. In hamsters the extent of infection was assessed by the appearance of flagellates in blood agar cultures of nose and spleen, by counting amastigotes in nose and liver impression smears, and by measuring the size of nose lesions. Ultrastructure of nose lesions before and after treatment with metronidazole or Pentostam was also evaluated. Infection in mice was assessed by the extent of parasitemia and/or survival to 30 days. In no case did metronidazole-treated animals differ from untreated controls. Metronidazole shows no activity against experimental infections of leishmaniasis or trypanosomiasis in these animal models.