Caerulomycin, an antifungal antibiotic with marked in vitro and in vivo activity against Entamoeba histolytica.

The anti-amoebic action of the bipyridyl antibiotic caerulomycin was assessed in vitro and in vivo using various strains of Entamoeba histolytica from polyxenic, axenic and monoxenic cultures. Minimum inhibition concentrations of caerulomycin (metronidazole) were 7.5 (5), 15.6(1.95) and 60 (2.5) micrograms/ml against polyxenic, axenic and monoxenic cultures of E. histolytica, respectively. The ED50 values ascertained in golden hamsters (extraintestinal amoebiasis) and rats (intestinal amoebiasis) after the oral route were 136 and 199 mg/kg (X4), respectively. Metronidazole proved to be approximately four times more active against tissue forms of E. histolytica than caerulomycin [ED50 of metronidazole: less than 40 mg/kg (X4)]. The antibiotic was slightly superior to metronidazole in its action on lumen forms of E. histolytica [ED50 of metronidazole: 233 mg/kg (X4)]. The antibiotic was in some cases toxic to hamsters and rats within the therapeutic range.