Anticryptosporidial activity of lasalocid and other ionophorous antibiotics in immunosuppressed rats.

The anticryptosporidial activities of three ionophorous antibiotics were assessed in dexamethasone-immunosuppressed rats infected with Cryptosporidium parvum. When administered prophylactically, lasalocid prevented infection in a dose-dependent manner, whereas monensin and salinomycin were ineffective. Therapeutically, lasalocid eliminated established overt infections of the intestine, although infection persisted in the common bile duct and intestinal infection recurred after lasalocid treatment was stopped. These findings suggest that lasalocid is a potentially useful anticryptosporidial agent but that long-term continuous administration may be necessary in the immunocompromised host.