The effect of butorphanol with or without subsequent methadone on the fentanyl requirements in dogs undergoing interventional cardiac procedures.

Methadone added to butorphanol premedication does not significantly reduce fentanyl requirements in cardiac intervention dogs.

This retrospective study investigated whether premedication with methadone, following butorphanol sedation, altered fentanyl requirements during anesthesia for interventional cardiac procedures in dogs. Twenty-three client-owned dogs received IV butorphanol (0.2–0.3 mg/kg) for echocardiography 60–90 minutes prior to anesthetic induction. Thirteen dogs also received methadone IM (0.5–1.1 mg/kg) or IV (0.26–0.3 mg/kg) approximately 30 minutes before induction. Anesthesia was induced with fentanyl, midazolam, and etomidate, and maintained with fentanyl, lidocaine, and isoflurane. No statistically significant differences were found between the butorphanol-only and butorphanol/methadone groups in induction fentanyl dose (5 vs. 9 μg/kg), etomidate dose, maintenance fentanyl infusion rate (7 vs. 5 μg/kg/hour), or lidocaine infusion rate. Cardiopulmonary parameters including prevalence of arrhythmias (9/10 vs. 8/13), hypotension (10/10 vs. 9/13), and arterial blood gas values were also not significantly different between groups. The high prevalence of hypotension and arrhythmias in both groups reflects the severity of underlying cardiac disease in these patients rather than drug effects. The study concludes that the addition of methadone to a butorphanol premedication protocol does not meaningfully reduce fentanyl requirements or improve cardiopulmonary stability in this population. Butorphanol alone may be a reasonable sedation choice prior to fentanyl-based anesthetic induction for interventional cardiac procedures in dogs.

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