Two blinded, placebo-controlled studies were designed to evaluate the efficacy of maropitant at a dose of 8 mg/kg for prevention of vomiting in dogs with a recent history of motion sickness. The first study was conducted at 3 veterinary clinics in the United States. The study was a 2-way crossover design that included 17 dogs. After an initial examination and confirmation of motion sickness, each dog was given either maropitant or placebo. The other treatment was then given 10 to 14 days later. One hour after either treatment, the dog was taken for a car ride that lasted at least 1 hour and was then brought to the veterinary clinic for an evaluation. A 70% proportional reduction in dogs that vomited after being treated with maropitant in comparison with placebo was found; however, the difference between the number of animals vomiting after each treatment was not statistically significant.

The second study was conducted at 30 veterinary clinics throughout Europe (France, Italy, United Kingdom) and was a parallel design study that included 211 dogs. A dog was eligible for the study if it had a history of motion sickness that included at least 1 incident of vomiting in the past 3 months. One hundred six dogs were treated with maropitant, and 105 dogs were given placebo. Each dog received a second dose of the same treatment about 24 hours later. This dose was used to evaluate the safety of the drug for intended label duration of up to 2 consecutive days of administration. As in the first study, 1 hour after being given the initial treatment the dog was taken for a car ride that lasted at least 1 hour and was then brought to the veterinary clinic for an evaluation. In the first study, 66% of the dogs given placebo vomited compared with 14% of those given maropitant. In this larger study, there was a 79% reduction in the proportion of the treated dogs that vomited-a statistically significant difference.

COMMENTARY: Maropitant citrate monohydrate (Cerenia; Pfizer Animal Health, is a neurokinin-1-receptor antagonist that has been developed for its antiemetic properties in dogs. Maropitant is formulated as a tablet, and the oral dose for the treatment or prevention of vomiting in dogs due to parvovirus, pancreatitis, and dietary indiscretion is 2 mg/kg; however, for prevention of motion sickness, the dose is 8 mg/kg. (Studies have indicated that this higher dose would be more effective while still retaining a good safety margin.) It is intended as a once-daily preventive treatment for motion sickness that can be given on 2 consecutive days. In these studies, no serious side effects were noted. Based on these results, it can be concluded that when maropitant is administered orally 1 hour before a car ride that lasts at least 1 hour, it is well tolerated and effective in preventing motion sickness in susceptible dogs.

Efficacy of maropitant for preventing vomiting associated with motion sickness in dogs. Benchaoui HA, Siedek EM, De La Puente-Redondo VA, et al. VET REC 161:444-447, 2007.