Aplastic anemia associated with trimethoprim-sulfadiazine and fenbendazole administration in a dog.

A dog that was treated with trimethoprim-sulfadiazine and fenbendazole developed transient aplastic anemia. The onset of bone marrow aplasia at 14 days after initiation of treatment and remission of it after cessation of treatment suggested that the aplasia was drug-induced. A hematologically normal dog treated with the same drug combination failed to develop hematologic dyscrasia. Because of the potential toxic effects of trimethoprim-sulfadiazine and/or fenbendazole, animals under treatment with this combination should be monitored by use of periodic CBC.