(P03) Pharmacokinetics of Oral Ondansetron in Hospitalized Dogs Exhibiting Clinical Signs of Nausea

Abstract:

Background: Oral ondansetron is commonly prescribed to dogs but pharmacokinetics in clinical patients have not been evaluated.
Hypothesis/

Objectives: To evaluate the pharmacokinetics of oral ondansetron in a population of hospitalized dogs exhibiting clinical signs of nausea.
Animals: Twenty-four client-owned dogs.

Methods: A prospective blinded study was performed. Dogs were randomly assigned to one of the following oral ondansetron protocols: 1 mg/kg q12h, 0.5 mg/kg q12h, 1 mg/kg q8h, 0.5 mg/kg q8h. Plasma was initially collected at 0, 0.25, 0.5, 1, 2, 4, 8, 16, 24h after the first dose in 7 dogs and was collected at 0, 2, 4, 8h in the remaining 17 dogs. Ondansetron concentrations were measured via high-performance liquid chromatography coupled to tandem mass spectrometry. Below limit of quantification (BLOQ) values were arbitrarily set at 1 ng/mL for statistical analysis. Plasma ondansetron concentrations were compared between groups using a Mann Whitney Test.

Results: Ondansetron concentrations were BLOQ in 18/36 (50%) samples in the 0.5 mg/kg groups and 14/36 (39%) samples in the 1 mg/kg groups. Plasma ondansetron concentrations were not significantly different between these groups [0.5 mg/kg group median 8.53 ng/mL; range 1-96.83 ng/mL and 1 mg/kg group median 7.43 ng/mL; range 1-278.67 ng/mL]. In six dogs, ondansetron was not detected at any timepoint.
Conclusions and Clinical Importance: Ondansetron was not detected in the plasma of multiple dogs after oral administration, raising concern for efficacy at currently recommended dosages.