The Pharmacokinetics of Intravenous and Subcutaneous Ondansetron in Female Beagle Dogs

The purpose of this study was to evaluate the pharmacokinetic profile of ondansetron following intravenous (IV) and subcutaneous (SC) administration in five healthy adult female Beagles. Dogs were administered ondansetron at 0.5 mg/kg IV and SC in a randomized crossover design. On day 0 ondansetron was administered either IV (OV group) or SC (OS group), and 7 days later administered via the opposite route. Plasma samples were collected, and heart and respiratory rates, and rectal temperature were recorded over an 8 h period. Ondansetron concentrations were quantified using liquid chromatography-tandem mass spectrometry. Non-compartmental analysis was performed using commercially available software. Median (min-max) peak plasma concentration following OS was 84.6 (56.0-326.1) ng/mL, which occurred at the first sampled time point of 0.25 (0.25-0.5) h. The terminal half-life was longer in the OS versus the OV group. Bioavailability of ondansetron in the OS group was 84.6 (51.2-132.6)%. Ondansetron administered SC at 0.5 mg/kg to adult healthy dogs has a similar bioavailability and a longer duration of action compared to the IV route of administration. Future pharmacokinetic and pharmacodynamic clinical studies should be performed in dogs utilizing the SC route of administration of ondansetron.