Sedative effects of hydromorphone or oxymorphone with or without acepromazine in dogs

Hydromorphone is an agonist opioid with potency approximately five times that of morphine and half that of oxymorphone. The purpose of this study was to compare hydromorphone with oxymorphone, with or without acepromazine, for sedation in dogs, and to measure plasma histamine before and after drug administration. Ten dogs received IM hydromorphone (H; 0.2 mg kg^?1), oxymorphone (O; 0.1 mg kg^?1), hydromorphone with acepromazine (H; 0.2 mg kg^?1, A; 0.05 mg kg^?1) or oxymorphone with acepromazine (O; 0.1 mg kg^?1, A; 0.05 mg kg^?1) in a randomized Latin‐square design. Sedation score, heart rate, respiratory rate, blood pressure, and SpO₂ were recorded at baseline and every 5 minutes after drug administration up to 25 minutes. Plasma histamine was measured at baseline and at 25 minutes post‐drug administration. Data were analyzed with repeated measures anova . Mean ± SD body weight was 21.62 ± 1.54 kg. Mean ± SD age was 1.07 ± 0.19 years. Sedation score was significantly greater for OA after 5 minutes than O alone (4.1 ± 3.5 versus 1.9 ± 1.5) and for HA after 15 minutes than H alone (8.6 ± 2.9 versus 5.9 ± 2.5). There was no significant difference in sedation between H and O at any time point. There was no significant difference between groups at any time with respect to heart rate, respiratory rate, blood pressure or SpO₂. Mean ± SD plasma histamine (nM ml^?1) for all groups was 1.72 ± 2.69 at baseline and 1.13 ± 1.18 at 25 minutes. There was no significant change in plasma histamine concentration in any group. Hydromorphone is effective for sedation in dogs and does not cause measurable increase in histamine. Sedation with hydromorphone is enhanced by acepromazine.