Effect of Intravenous Administration of Cobalt Chloride to Horses on Clinical and Hemodynamic Variables

BACKGROUND Cobalt chloride (CoCl2 ) is administered to racehorses to enhance performance. The purpose of this study was to evaluate the clinical, cardiovascular, and endocrine effects of parenterally administered CoCl2 . OBJECTIVES To describe the effects of weekly intravenous doses of CoCl2 on Standardbred horses. ANIMALS Five, healthy Standardbred mares. METHODS Prospective, randomized, experimental dose-escalation pilot. Five Standardbred mares were assigned to receive 1 of 5 doses of CoCl2 (4, 2, 1, 0.5, or 0.25 mg/kg) weekly IV for 5 weeks. Physical examination, blood pressure, cardiac output, and electrocardiography (ECG) were evaluated for 4 hours after administration of the first and fifth doses. Blood and urine samples were collected for evaluation of cobalt concentration, CBC and clinical chemistry, and hormone concentrations. RESULTS All mares displayed pawing, nostril flaring, muscle tremors, and straining after CoCl2 infusion. Mares receiving 4, 2, or 1 mg/kg doses developed tachycardia after dosing (HR 60-126 bpm). Ventricular tachycardia was noted for 10 minutes after administration of the 4 mg/kg dose. Increases in systolic arterial pressure (SAP), diastolic arterial pressure (DAP), and mean arterial pressure (MAP) occurred after administration of all doses (4, 2, 1, 0.5, and 0.25 mg/kg). Profound hypertension was observed after the 4 mg/kg dose (SAP/DAP, MAP [mmHg] = 291-300/163-213, 218-279). Hemodynamics normalized by 1-2 hours after administration. ACTH and cortisol concentrations increased within 30 minutes of administration of all CoCl2 doses, and cardiac troponin I concentration increased after administration of the 4 and 2 mg/kg doses. CONCLUSIONS AND CLINICAL IMPORTANCE The degree of hypertension and arrhythmia observed after IV CoCl2 administration raises animal welfare and human safety concerns.