Objective—To evaluate the effect of dosing interval on the efficacy of maropitant for prevention of opioid-induced vomiting and signs of nausea in dogs.

Design—Randomized prospective clinical study.

Animals—50 client-owned dogs that underwent an elective surgical procedure.

Procedures—Dogs were randomly assigned to receive maropitant (1 mg/kg [0.45 mg/lb], SC), then hydromorphone (0.1 mg/kg [0.045 mg/lb], IM) at 0 (simultaneously; group 0; n = 10), 15 (group 15; 10), 30 (group 30; 10), 45 (group 45; 10), or 60 (group 60; 10) minutes later. Dogs were monitored for vomiting and signs of nausea for 30 minutes after hydromorphone administration. A historical control group of similar dogs (n = 9) that were administered hydromorphone (0.1 mg/kg, IM) but not maropitant served as the referent for comparison purposes.

Results—Vomiting was recorded for 6 dogs in group 0 and 2 dogs in group 15. Signs of nausea were recorded for 10 dogs in group 0, 9 dogs in group 15, 8 dogs in group 30, 6 dogs in group 45, and 1 dog in group 60. Compared with dogs in the historical control group, vomiting was significantly decreased and prevented when maropitant was administered 15 and 30 minutes, respectively, before hydromorphone; signs of nausea were significantly decreased only when maropitant was administered 60 minutes before hydromorphone.

Conclusions and Clinical Relevance—Results indicated that vomiting was significantly decreased and then prevented when maropitant was administered to dogs 15 and 30 minutes before hydromorphone. However, signs of nausea were significantly decreased only when the dosing interval was 60 minutes.