Anaphylaxis due to First-Time Intravenous Infusion of N-Acetylcysteine in a Dog

A 4-year-old female spayed Pomeranian was referred to the emergency service for intermittent trouble breathing and an enlarged liver found on ultrasound. A severe mixed hepatopathy was found on bloodwork, and ultrasound-guided liver aspirates showed marked hepatocellular vacuolar changes and rare neutrophils. An intravenous (IV) loading dose of n-acetylcysteine (NAC) was given for the first time in this patient, and immediately after the infusion the patient collapsed, became hypotensive, hypothermic, tachycardic, and developed gallbladder wall edema. Treatment for anaphylaxis was immediately initiated with IV fluids, an epinephrine bolus and then continuous rate infusion, diphenhydramine, and famotidine. Clinical signs resolved within an hour of treatment with no recurrence. The hepatic enzymopathy improved, and the patient was ultimately diagnosed with a steroid hepatopathy based on laparoscopic liver biopsies. Anaphylaxis caused by first-time administration of IV NAC in a dog has not previously been reported, though it is known to occur in humans. Based on this report, it would be clinically wise to give careful consideration before prescribing NAC in cases where it is not a specific antidote or if other options are available, and to closely monitor the patient during and immediately after administration.