Equine Ionophore Toxicity Study Guide

Overview and Clinical Importance

Ionophore toxicity is a life-threatening emergency in horses caused by accidental ingestion of ionophore antibiotics (monensin, salinomycin, lasalocid, narasin) intended for cattle, poultry, and other livestock. Horses are extraordinarily sensitive - 10-20 times more than cattle. Ionophores cause severe cardiomyopathy, myocardial necrosis, arrhythmias, and often sudden death.

What Are Ionophores?

Definition and Mechanism

Ionophores are lipid-soluble compounds that transport ions across cell membranes. They have a hydrophilic interior (binds cations) and hydrophobic exterior (crosses lipid bilayers). Ionophores disrupt normal ionic gradients by facilitating unregulated ion transport, causing cellular dysfunction and death in cardiac and skeletal muscle.

Common Ionophores in Veterinary Medicine

Species Sensitivity and Toxic Doses

Horses are 10-20 times more sensitive than cattle and 200 times more sensitive than poultry. Factors: pharmacokinetic differences, cardiac muscle sensitivity, lack of ruminal buffering.