Bioavailability of Oral Ondansetron in Dogs: A Crossover Study.

Area of Science:

• Veterinary Pharmacology
• Drug Pharmacokinetics
• Canine Therapeutics

Background:

• Ondansetron is a common antiemetic used in veterinary medicine.
• Understanding oral drug bioavailability is crucial for effective therapeutic dosing.
• Limited pharmacokinetic data exists for oral ondansetron in dogs.

Purpose of the Study:

• To compare the pharmacokinetics of oral (PO) versus intravenous (IV) ondansetron in healthy dogs.
• To determine the oral bioavailability of ondansetron in a canine model.
• To assess the potential efficacy of oral ondansetron dosing in dogs.

Main Methods:

• Eight healthy dogs received PO and IV ondansetron (1 mg/kg) in a crossover design.
• Plasma ondansetron concentrations were measured using liquid chromatography/mass spectrometry.
• Pharmacokinetic parameters, including Cmax and AUC0-8h, were calculated.

Main Results:

• Intravenous ondansetron showed high plasma concentrations (AUC0-8h: 1181 ± 619 ng/mL*h).
• Oral ondansetron resulted in low Cmax (22 ± 11.3 ng/ng/mL) and AUC0-8h (61.7 ± 45.4 ng/mL*h).
• Mean oral bioavailability was estimated at a low 5.2% ± 2.1%.

Conclusions:

• Oral bioavailability of ondansetron is significantly low in healthy dogs at the recommended dose.
• The efficacy of 1 mg/kg oral ondansetron in dogs is questionable due to poor absorption.
• Further pharmacodynamic studies in nauseous dogs are needed to confirm clinical relevance.