Cardiovascular Complications of Minoxidil Toxicosis in Two Dogs

A 3 yr old female spayed golden retriever and a 9 mo old female spayed mixed-breed dog were evaluated at separate veterinary hospitals for ingestion of oral minoxidil tablets at dosages of 1.1 and 1.52 mg/kg, respectively. Decontamination was initiated in both dogs. Both dogs were hospitalized and developed sinus tachycardia. Both dogs developed hypotension, with one requiring vasopressor therapy. Both dogs were treated with antiarrhythmic medications and one dog received IV injectable lipid emulsion therapy. Markedly elevated serum cardiac troponin I (TnI) values were reported in both dogs during hospitalization, indicating myocardial damage. Both dogs had resolution of clinical signs by the second day of hospitalization and were discharged. A TnI measurement was obtained in one dog weeks after discharge and was within normal limits, whereas the other showed significant improvement in TnI levels during hospitalization. Minoxidil has long been recognized as a cardiovascular toxin in dogs and cats. Existing reports of minoxidil toxicosis in pets involve the topical formulation of the drug. To the authors' knowledge, this is the first report of toxicity involving the oral formulation of minoxidil and the first reported instance of minoxidil-related acute myocardial injury with clinical resolution and marked reduction in TnI levels.