5-fluorouracil toxicity with severe bone marrow suppression in a dog.

This report describes 5-fluorouracil (5-FU) toxicity in a dog that resulted in severe bone marrow suppression. The dog initially was presented with neurologic and gastrointestinal signs and developed pancytopenia characterized by severe neutropenia and thrombocytopenia. Examination of bone marrow aspirate showed aplasia. The dog also had marked echinocytosis, which has been previously associated with in vitro 5-FU exposure. The patient was given aggressive supportive care and recovered within 25 d of exposure. To the authors' knowledge, this is the first report of a case of 5-FU toxicity in a dog to include results of bone marrow examination, as well as the first to describe echinocytosis related to 5-FU toxicity.