Investigating which opioid has the greatest sedative effects in conjunction with acepromazine
The sedative acepromazine only produces mild sedation and has no analgesic effects; increasing the dose of acepromazine does not increase the level of sedation and may only intensify any adverse effects. So if more intense sedation is needed, various drugs, including opioids, are often given in addition to the acepromazine. A recent study in Veterinary Anaesthesia and Analgesia looked at four opioids--butorphanol, methadone, morphine, and tramadol--to compare the levels of sedation achieved with each of the opioids when given in combination with acepromazine. The researchers also looked for specific adverse effects by monitoring respiratory rate, pulse rate, systolic arterial pressure, and rectal temperature. Six dogs were used in the cross-over study. They received the acepromazine intravenously and then one of the four opioids intravenously 15 minutes later. A washout period of at least one week was used between each of the four drugs in the six dogs.
The most sedation was seen with methadone and acepromazine. Butorphanol or morphine in combination with acepromazine also provided a moderate sedation level. Tramadol and acepromazine did not improve the sedation level compared with acepromazine alone, so the authors did not recommend this combination if moderate sedation is needed. The peak level of sedation for all four opioids was 30 to 45 minutes after administration. No clinically significant adverse effects were noted in the study, although the pulse rate decreased in dogs receiving acepromazine and morphine, butorphanol, or tramadol. And rectal temperatures were lower in dogs receiving acepromazine and morphine or methadone. One of the dogs vomited after receiving acepromazine and morphine, so the authors recommended using a different opioid if vomiting should be avoided.
Monteiro ER, Junior AR, Assis HM, et al. Comparative study on the sedative effects of morphine, methadone, butorphanol or tramadol, in combination with acepromazine, in dogs. Vet Anaesth Analg 2009;36(1):25-33.
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