Pancytopenia in two horses following administration of potentiated sulfonamide antimicrobials

Adverse drug reactions to potentiated sulfonamide antimicrobial drug combinations have been reported in many species, including horses. This report describes the occurrence of pancytopenia in 2 horses, one subsequent to an immune mediated reaction and the other bone marrow aplasia following the administration of trimethoprim and sulfadimidine. These cases highlight the importance of judicious use of antimicrobial agents and describe adverse drug reactions in horses receiving potentiated sulfonamide antimicrobials.