Amiodarone-induced anaphylaxis in a Chihuahua: a case report

Amiodarone, a class III antiarrhythmic drug, is widely used in both human and veterinary medicine to manage ventricular and supraventricular arrhythmias. While its efficacy in rhythm control is well-established, the drug is associated with significant adverse effects, affecting multiple organ systems. In humans, amiodarone-induced toxicity commonly involves the pulmonary, hepatic, thyroid, and dermatological systems, with pulmonary toxicity being one of the most severe complications. Acute hypersensitivity reactions, including anaphylaxis, are rare but have been reported, particularly in association with intravenous (IV) formulations containing polysorbate 80. In veterinary medicine, amiodarone is increasingly used to treat life-threatening arrhythmias in dogs, yet its safety profile is less extensively studied. Unlike humans, dogs appear to be more susceptible to immediate hypersensitivity reactions following IV administration, characterized by severe cutaneous signs, hypotension, and cardiovascular collapse. The present case report describes a 9-year-old Chihuahua that developed a rapid hypersensitivity reaction, including erythema, mucosal hyperemia, and facial edema, immediately after receiving IV amiodarone. The reaction resolved spontaneously within 15 minutes without requiring corticosteroid administration. Haematological and biochemical analyses showed a mildly decreased reticulocyte value, elevated neutrophil count, and increased ALT, while all other parameters were within reference ranges. A review of the literature suggests that excipients such as polysorbate 80 and benzyl alcohol may be primary contributors to amiodarone-induced anaphylaxis in dogs. Histamine-mediated responses, severe hypotension, and cardiovascular complications have been documented in both human and veterinary cases, with dogs displaying heightened sensitivity to IV administration. Additionally, while pulmonary and thyroid toxicity are well-recognized chronic effects in human patients, hepatic and gastrointestinal toxicities are more frequently observed in dogs. This case underscores the need for heightened awareness of amiodarone-induced hypersensitivity reactions in veterinary medicine, particularly in IV formulations. Pre-medication strategies, controlled infusion rates, and close monitoring are essential to mitigating the risk of life-threatening anaphylaxis in human and canine patients. Further research is needed to better understand species-specific differences in amiodarone metabolism and toxicity.