Studies have shown that neurokinin1 (NK1) receptor antagonists have broad-spectrum antiemetic activity to both centrally and peripherally acting emetogens. The antiemetic efficacy of maropitant, a highly specific NK1 receptor antagonist, was compared with the activity of 3 other antiemetic drugs commonly used to control emesis in dogs. In these 2 studies, each of 20 dogs was given each of 5 different treatments singly, with a 7-day washout period between treatments. The 5 treatments were 0.9% saline (0.1 mL/kg), maropitant (1 mg/kg SC), metoclopramide (0.5 mg/kg SC), chlorpromazine (0.5 mg/kg SC), and ondansetron (0.5 mg/kg IV). One hour after each treatment, dogs were challenged with a centrally acting emetogen (apomorphine, 0.1 mg/kg IV; study 1) or a peripherally acting emetogen (syrup of ipecac, 0.5 mg/kg PO; study 2). Emetic events (active retching or vomiting) were then counted and recorded. The study found maropitant, metoclopramide, and chlorpromazine to be similarly efficacious in their ability to significantly reduce emetic events in dogs given apomorphine, whereas emesis was not reduced after ondansetron treatment. In dogs given syrup of ipecac, maropitant and ondansetron were similarly efficacious in preventing emesis, whereas no significant reduction in emesis occurred after metoclopramide or chlorpromazine treatment. Other than emesis, no abnormal clinical signs or adverse events were noted in either study. The investigators conclude that only maropitant was effective in controlling emesis from both central and peripheral challenges.

•  Compared antiemetic maropitant to metoclopramide, chlorpromazine, ondansetron, and saline (control).
•  Central-acting emetogen (apomorphine):
    -Efficacy of maropitant same as that of metoclopramide and chlorpromazine
    -Efficacy of maropitant superior to that of ondansetron
•  Peripheral-acting emetogen (syrup of ipecac):
    -Efficacy of maropitant same as that of ondansetron
    -Efficacy of maropitant superior to that of metoclopramide and chlorpromazine
•  Maropitant effective in controlling emesis from both central and peripheral challenges

Comparative efficacy of maropitant and selected drugs in preventing emesis induced by centrally or peripherally acting emetogens in dogs. Sedlacek HS, Ramsey DS, Boucher JF, et al. J VET PHARMACOL THER 31:533-537, 2008.