Bone marrow hypoplasia associated with fenbendazole administration in a dog

A 1.5-year-old Doberman pinscher was presented with sudden-onset of fever and malaise. Twelve days prior to presentation, fenbendazole therapy was initiated for a suspected lungworm infection. Results of a complete blood count on presentation showed pancytopenia, while histopathological evaluation of a bone marrow core sample revealed bone marrow hypoplasia of undetermined etiology. Bactericidal antibiotics and fluid therapy, as well as discontinuation of fenbendazole administration, led to a complete resolution of clinical and hematological abnormalities within 15 days. An idiosyncratic reaction to fenbendazole was suspected based on the absence of infectious, neoplastic, autoimmune, and toxic etiologies, as well as resolution of clinical signs and pancytopenia upon drug withdrawal.