Comparison of premedication with or without vatinoxan, co-administered with medetomidine and methadone, in anesthetized dogs

Vatinoxan, a peripheral alpha-2 antagonist, mitigates the cardiovascular effects of medetomidine but may cause hypotension during general anesthesia and alter the plasma concentrations of co-administered sedatives and analgesics. This study compares the effect of premedication with or without vatinoxan co-administered with medetomidine and methadone on sedation quality, cardiovascular and respiratory variables, and methadone plasma concentration in anesthetized dogs. Twenty healthy dogs undergoing elective ovariectomy were premedicated with methadone (0.2 mg/kg) and medetomidine (0.15 mg/m²), with vatinoxan (3 mg/m²) in group MV or without vatinoxan in group M. Sedation was assessed using a 21-point scale. Anesthesia was induced 20 min after and maintained with isoflurane. Cardiovascular and respiratory variables were recorded 15 min post-premedication, at traction on both ovarian pedicles, 90 min after premedication and at skin suture. Methadone plasma concentration was measured at 15, 90, and 240 min post-premedication. Sedation scores were significantly higher in group MV at 10 min post-premedication (p = 0.014). Only in group M, heart rate decreased significantly after premedication (p < 0.001). Vatinoxan administration did not affect intraoperative cardiovascular variables during nociceptive stimulation or in its absence. Hypotension was not observed in any dog. Time to recover from anesthesia and postoperative analgesia were not different between groups. Plasma methadone concentrations in group MV were not statistically different from group M, though slightly higher at 15 min post-premedication. For elective ovariectomy, adding vatinoxan to medetomidine and methadone provides rapid sedation, stable cardiovascular function during anesthesia, and smooth recovery causeing non-relevant variations in methadone plasma concentrations.