The neurokinin-1 (NK-1) receptor antagonist,
maropitant citrate, mitigates
nausea and
vomiting in dogs and cats.
Nausea is poorly understood in horses, and clinical use of
NK-1 receptor antagonists has not been reported. This study aimed to determine the pharmacokinetics and safety of
maropitant after administration of multiple doses. We hypothesized that
maropitant concentrations would be similar at steady state to those reported in dogs, with minimal adverse effects.
Maropitant was administered at 4 mg/kg orally, once daily for 5 days in seven adult horses. Serial plasma
maropitant concentrations were measured by liquid chromatography-mass spectrometry. Noncompartmental pharmacokinetic parameters were determined. The maximum, minimum, and average concentrations of
maropitant achieved at steady state were 375.5 ± 200, 16.8 ± 7.7, and 73.5 ± 45.1 ng/ml, respectively. The terminal elimination half-life was 11.6 ± 1.4 hr, and the accumulation index was 1.3 ± 0.07. Heart rate decreased between Day 1 and Day 5 (p = .005), with three horses having heart rates of 20 beats per minute and
atrioventricular block on Day 5. Pharmacokinetics of repeated
maropitant administration suggests the
drug could be considered for use in healthy horses. Further investigation on the clinical relevancy of its cardiac effects is warranted.