# Incidence of Post-Sedation Emesis in Cynomolgus (Macaca fascicularis) and Rhesus (Macaca mulatta) Macaques, and Evaluation of Prophylactic Antiemetic Efficacy

## TL;DR

Cynomolgus macaques experience more vomiting after ketamine sedation than rhesus macaques, and ondansetron shows some effectiveness in reducing this.

## Contribution

This study identifies species and sex as predictors of emesis in macaques and evaluates antiemetic efficacy in cynomolgus macaques.

## Key findings

- Cynomolgus macaques had a 55% emesis rate compared to 2.6% in rhesus macaques.
- Ondansetron reduced emesis incidence to 33%, showing clinical effectiveness despite not being statistically significant.
- Maropitant citrate did not significantly reduce emesis in cynomolgus macaques.

## Abstract

A retrospective analysis of 70 ketamine sedation events in rhesus and cynomolgus macaques identified this species as a predictor of emesis, with cynomolgus macaques having a higher incidence of emesis (55%) than rhesus macaques (2.6%). Female cynomolgus macaques had a higher incidence of emesis than males. Next, we conducted a prospective study to assess the efficacy of antiemetics in preventing vomiting. Maropitant citrate, ondansetron, or a placebo was given to cynomolgus macaques prophylactically before a sedation event. Emesis was reduced from 58% in the control group to 50% in the maropitant group and 33% in the ondansetron group. Although the reduction in relative risk was not statistically significant, orally administered ondansetron demonstrated a clinically meaningful reduction in the incidence of vomiting in cynomolgus macaques following ketamine sedation.

Emesis is one of the most common side effects of ketamine sedation; however, predictors like species and sex have not been studied in macaques. This study aimed to determine the incidence and predictors of emesis in macaques undergoing ketamine sedation and to assess the efficacy of orally administered antiemetics in preventing emesis. A retrospective analysis was performed using medical records from rhesus and cynomolgus macaques who received ketamine sedation for veterinary examination events from August 2023 to April 2024. Among the 70 sedations performed using IM ketamine, the overall incidence of emesis was 26%. Cynomolgus macaques had a significantly higher risk of emesis (odds ratio (OR) 46.14, 95% confidence interval (CI): 7.08–493.9; p < 0.0001), with an emesis incidence of 55%. Females showed a higher incidence of emesis (75%) with an odds ratio of 3.72 (95% CI: 0.55–17.91; p = 0.24), though this difference was not statistically significant. In a prospective, randomized study, we compared the prophylactic use of oral maropitant citrate at a dose of 2 mg/kg or oral ondansetron at a dose of 1 mg/kg versus placebo for the prevention of emesis in cynomolgus macaques undergoing veterinary examination. Emesis was reduced from 58% in the control group to 50% in the maropitant group and 33% in the ondansetron group. However, the reduction in relative risk with either treatment did not reach statistical significance. Prophylactic oral administration of maropitant appears ineffective in preventing emesis in cynomolgus macaques. In contrast, prophylactic oral ondansetron is a more effective alternative in preventing emesis in these animals.