Ondansetron in dogs with nausea associated with vestibular disease: A double‐blinded, randomized placebo‐controlled crossover study

Background Nausea and emesis can be, among other signs, common manifestations of acute vestibular system dysfunction in dogs. Currently, antiemetic drugs, such as maropitant and metoclopramide, are used commonly, but do not appear to control nausea. A non‐placebo‐controlled preliminary study suggested good efficacy of 5‐HT3‐receptor antagonists, such as ondansetron, against nausea in dogs with vestibular syndrome. Objectives To assess and confirm the effect of ondansetron on behavior suggestive of nausea in dogs with vestibular syndrome. Animals Fourteen dogs with vestibular syndrome and clinical signs of nausea presented to a neurology service. Methods Placebo‐controlled, double‐blinded, crossover study. Behavioral assessment was performed hourly for 4 hours using an established numerical rating scale. The criteria salivation, lip licking, vocalization, restlessness, lethargy, and general nausea were scored. The occurrence of emesis was recorded. After scoring at T0 (pre‐dose) and T2 (2 hours post‐dose) either ondansetron (0.5 mg/kg) or placebo was injected IV. Two hours post‐dose, treatments were switched. Blood samples were collected to measure serum arginine vasopressin (AVP) concentration, which previously has been shown to correlate with clinical signs of nausea. Results Clinical resolution of nausea was observed 1 hour after administration of ondansetron, whereas serum AVP concentration decreased 4 hours after ondansetron administration. Conclusion and Clinical Importance Administration of ondansetron IV is beneficial for dogs with nausea secondary to acute vestibular syndrome. Ondansetron substantially and rapidly decreased clinical signs of nausea behavior and stopped emesis.