Sedative effects of methadone combined with medetomidine alone, or with medetomidine and vatinoxan in dogs

Vatinoxan, a peripheral alpha-2 antagonist, mitigates medetomidine's cardiovascular effects. This study compared sedation quality and cardiovascular variables in healthy dogs given methadone and medetomidine, with or without vatinoxan. This study enrolled healthy dogs, undergoing elective midline ovariectomy. The animals were randomly assigned to two groups: one group received IM methadone (0.2 mg kg-1) with medetomidine (0.15 mg m-2) (group MM), and the other group received the same combination plus vatinoxan (3 mg m-2) (group MVM). Sedation was evaluated using a 21-point scale (Grint et al. 2009) at 5, 10, and 15 minutes post-administration, with scores 3 to 6 considered mild sedation. HR was measured before sedation and at 15 minutes, and systemic arterial blood pressure was measured using oscillometry. Group differences were analysed using a Student’s t-test or Wilcoxon test. A linear mixed model was used to analyse HR and MAP over time. Statistical significance was set at p < 0.05 Sixteen dogs weighing 2.5 to 46 kg were enrolled. Compared to group MM, group MVM had a statistically higher weight (p = 0.014) and body surface area (p = 0.012). Medetomidine dose was not significantly different between dogs (p = 0.760), and was 5.8 ± 3.1 and 5.5 ± 0.9 μg kg-1 in MM and MVM groups, respectively. The sedation was mild in 2 MVM dogs; the other animals were scored ≥ 8. IV catheter was inserted in all animals. HR decreased significantly (p < 0.001) in both groups, with an overall median (range) of 68 (42-100) bpm. MAP remained above 70 mmHg. Both protocols may provide similar sedation for IV catheter insertion with cardiovascular stability. However, dogs receiving medetomidine and vatinoxan exhibited more variability in sedation compared to those receiving medetomidine alone, suggesting the need for higher doses of the combination to achieve consistent sedation levels.