Clinical toxicology of an antibiotic ionophore (monensin) in ponies and horses; diagnostic markers and therapeutic considerations

Abstract

Toxicity of the ionophorous antibiotic monensin has been documented in a number of species, with the horse showing greatest sensitivity. This study examined haemodynamic, renal, erythrocytic, and biochemical variables to determine mechanisms of equine monensin toxicosis, and potential therapy. Horse and pony mares were fitted uith catheters for blood and urine collection, then given monensin orally. Other studies were carried out in anaesthetized ponies, which received an intravenous dose of monensin. Cardiovascu1ar effects included pressor and positive inotropic responses, myocardial lesions postmortem, and increased pericardial fluid CK and LDH, Renal disturbances noted were rises in BUN and in clearance of phosphorus and potassium, decline in urine pH, and elevated urine N-acety1g1ucosaminidase. Erythrocytic responses included a rise in unconjugated serum bilirubin, increased red cell osmotic fragility, and altered blood gas variables.