Electrocardiographic and cardiopulmonary effects of intramuscular administration of glycopyrrolate and romifidine in conscious beagle dogs.

Objective To determine the electrocardiographic and cardiopulmonary effects of IM administration of romifidine with and without prior administration of glycopyrrolate in conscious dogs. Study design Prospective randomized study. Animals Twelve healthy, adult beagles. Materials and methods Dogs were assigned at random to each of three treatments with glycopyrrolate (six dogs), and to each of three treatments without glycopyrrolate (six dogs). Baseline data were recorded, and saline solution or glycopyrrolate (10 µg kg) was given IM. After 15 minutes, saline solution (control) or romifidine (20 or 40 µg kg) was given IM. An ECG, heart rate (HR), systemic blood pressures, and respiratory rate (RR) were recorded before and 2.5, 5, 10, 15, 30, 45, 60, 75, 90, 105 and 120 minutes after romifidine administration. Rectal temperature (RT), pH, PaCO, PaO, hematocrit and plasma protein were determined before and 15, 30, 60 and 120 minutes after romifidine administration. Data were analyzed using analysis of variance for repeated measures and Tukey multiple comparison tests. Results Without glycopyrrolate, HR (beats minute) decreased to minimum values (mean ± SD) of 52 ± 7 and 49 ± 12 (control 89 ± 20) 45 minutes after administration of romifidine at doses of 20 and 40 µg kg, respectively. Sinus bradycardia (HR < 60 beats minute), which persisted for up to 120 minutes, was observed in five of six and six of six dogs given romifidine at doses of 20 and 40 µg kg, respectively. With glycopyrrolate, decreases in HR were prevented and mean arterial pressure (mm Hg) increased to maximum values of 139 ± 25 and 173 ± 17 (control 113 ± 11) 30 minutes after administration of romifidine at doses of 20 and 40 µg kg, respectively. With and without glycopyrrolate, RR did not change appreciably, RT decreased, and pH, PaCO, PaO, hematocrit and plasma protein did not change after administration of romifidine. Conclusions and clinical relevance In healthy conscious beagles, IM administration of romifidine at doses of 20 and 40 µg kg causes sinus bradycardia which persists for up to 120 minutes. Administration of glycopyrrolate 15 minutes before administration of romifidine, prevents sinus bradycardia and induces moderate increases in arterial pressure.