Effectiveness of Ondansetron for Treating Nausea in Dogs with Vestibular Syndrome

Treatment of vestibular disease is usually multimodal and includes treating underlying disease, when present, and providing supportive care for emesis and nausea. Drugs currently approved in veterinary medicine for management of nausea and vomiting include metoclopramide (a dopamine D₂ receptor antagonist) and maropitant (a neurokinin-1 receptor antagonist). Both of these drugs can manage vomiting but lack antinausea properties when compared with placebo.^1,2

Ondansetron (a 5-HT₃ receptor antagonist) can eliminate nausea and vomiting in dogs^2,3 and alleviates signs of kinetosis (ie, motion sickness), presumably due to the high distribution rate of 5-HT₃ receptors in the area postrema.^4,5 The area postrema lacks a specific blood–brain diffusion barrier to large polar molecules, and its specialized cells are therefore able to detect emetic toxins in the blood and CSF. Along with the nucleus of the solitary tract, this area is responsible for generating nausea and emesis.⁶ 

Nausea is a multidimensional sensation affected by vestibular inputs and other factors (eg, GI stimulation, physical and psychological factors)⁷ and is easier to quantify in humans, as they can report its existence and severity. Behavior and facial expressions are used in dogs and cats to evaluate the level of nausea, making it harder to quantify. 

This study evaluated ondansetron as an antinausea drug in 16 dogs with nausea due to vestibular disease; only 31.3% of the dogs also had emesis. The intensity of nausea-like behavior (ie, salivation, lip licking, restlessness, lethargy, vocalization) was evaluated using a severity numeric scale prior to ondansetron administration (0.5 mg/kg IV) and 2 hours posttreatment. The occurrence and frequency of salivation, lip licking, restlessness, lethargy, and vomiting were significantly decreased in 11 dogs after ondansetron administration. The level of vocalization did not change.

Key pearls to put into practice:

Increased awareness of the difference between a drug’s antiemetic and/or antinausea effects is warranted. Medical management of nausea and emesis in dogs and cats can improve patient care.

Five nausea-like behaviors were scored in this study: salivation, lip licking, restlessness, lethargy, and vocalization. Apart from vocalization, nausea-like behaviors significantly decreased after ondansetron administration. All of these behaviors should be considered in dogs with vestibular disease as potential signs of nausea.

Although all dogs in this study showed signs of nausea prior to drug administration, only 31.3% had emesis, supporting the idea that nausea and emesis can occur separately. Antinausea treatment should be considered in dogs with vestibular signs regardless of emetic status. Ondansetron (0.5 mg/kg IV) was beneficial in this preliminary study.