Retrospective Determination of the Incidence of Apparent Type I Hypersensitivity Reaction to Intravenous Amoxicillin–Clavulanate in Dogs and Cats

OBJECTIVE: To determine the incidence of, and characterize the clinical signs associated with, apparent type I hypersensitivity (HS) reactions due to administration of a new formulation of IV amoxicillin-clavulanate (AC). DESIGN: Observational retrospective study. SETTING: Two private specialty hospitals in New South Wales, Australia. ANIMALS: One thousand six hundred seventy-two dogs and cats administered a new formulation of IV AC. MEASUREMENTS AND MAIN RESULTS: Between September 2018 and May 2022, patients were identified that received chlorpheniramine or dexamethasone within 6 h of receiving the new formulation of IV AC, had an allergy alert to the new formulation noted in the medical record, or had an allergy or suspected reaction to the new formulation described in the medical record. Patients were included if the new formulation was administered, if they had evidence of a type I HS reaction within 6 h of injection, and if they were administered treatment for a type I HS reaction. Eleven dogs (and no cats) had an apparent type I HS reaction (incidence 0.81% for dogs). Cases were clustered between November 2021 and May 2022 (n = 10), with an incidence of 2.13% for dogs. Dermatologic signs were recorded for all cases (n = 11), with some showing cardiovascular (n = 2) or gastrointestinal signs (n = 1). All cases survived. CONCLUSIONS: The incidence of a type I HS reaction to the new formulation of IV AC in dogs was low, and the outcome was excellent. No reactions in cats were identified. A cause for clustering of cases within a 6-month period was not elucidated.