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Effects of three methadone doses combined with acepromazine on sedation and some cardiopulmonary variables in dogs

Bitti, Flavia S., Campagnol, Daniela, Rangel, Julia PP., Nunes Junior, Juarez S., Loureiro, Bárbara, Monteiro, Eduardo R.
Veterinary anaesthesia and analgesia 2017 v.44 no.2 pp. 237-245
acepromazine, acidosis, adults, adverse effects, blood gases, blood pressure, dogs, heart rate, methadone, sedation, temperature
To evaluate the sedative and cardiopulmonary effects of three methadone doses, combined with acepromazine, in dogs.Prospective, randomized, complete block study.Six healthy, adult, cross-bred dogs weighing 17.2±4.4 kg (mean±standard deviation).Each dog was administered four treatments: acepromazine (0.05 mg kg−1) alone or acepromazine (same dose) in combination with methadone (0.25, 0.50 or 0.75 mg kg−1). All drugs were administered intramuscularly. Sedation was scored by a numeric descriptive scale (NDS, range 0–3) and a simple numerical scale (SNS, range 0–10). Heart rate, invasive blood pressure, arterial blood gases and rectal temperature were measured at 15 to 30 minute intervals for 120 minutes.According to NDS scores, mild to moderate sedation (NDS=1–2) was observed in most dogs in the acepromazine treatment, with only one out of six dogs scored as exhibiting intense sedation (NDS=3). All treatments with methadone resulted in significantly higher SNS scores compared with acepromazine alone. In these treatments, most dogs exhibited intense sedation (NDS=3). Increasing the dose of methadone from 0.25 to 0.50 or 0.75 mg kg−1 prolonged sedation in a dose-related manner, but did not influence the degree of sedation. The main adverse effects following administration of acepromazine–methadone treatments were decreased blood pressure, mild respiratory acidosis and decreased rectal temperature. These effects were well tolerated and resolved without treatment.In this study in six dogs, acepromazine–methadone administration resulted in intense sedation in most dogs. The results are interpreted to indicate that a low dose of methadone (0.25 mg kg−1) administered in combination with acepromazine (0.05 mg kg−1) will induce short-term sedation in dogs, whereas higher doses of methadone should be administered when prolonged sedation is desired.