Clinical effects of vatinoxan co-administered with medetomidine and methadone in healthy dogs undergoing isoflurane anaesthesia

Vatinoxan mitigates the cardiovascular effects of medetomidine but may cause hypotension during general anaesthesia and may alter plasma concentrations of co-administered analgesics (Kallio-Kujala et al., 2022). This study examines cardiovascular variables and methadone plasma levels in anesthetized dogs premedicated intramuscularly with vatinoxan, medetomidine, and methadone. This study enrolled 16 healthy dogs, weighing 2.5 to 46 kg, undergoing elective midline ovariectomy. The animals received medetomidine (0.15 mg m-2) and methadone (0.2 mg kg-1) premedication with vatinoxan (3 mg m-2; group MVM) or without vatinoxan (group MM). Anaesthesia was induced with propofol 20 minutes after the injection and maintained with isoflurane in oxygen. Clinical variables, including HR, non-invasive MAP, and end-tidal concentration of isoflurane (EtISO), were recorded at maximal traction of both ovarian pedicles and at skin suture. Methadone plasma concentration (cM) was measured at 15 (T15) and 90 (T90) minutes after premedication. Propofol dose and cM were compared between groups with a Student’s t-test, and a linear mixed model was used to analyse the effect of time and group on clinical variables. Propofol dose did not differ between groups. Time and group did not show any statistically significant effects on haemodynamic and respiratory variables. During anaesthesia, mean HR was 76 ± 21 and 91 ± 22 beats minute-1 and mean MAP was 88 ± 14 and 94 ± 16 mmHg in group MM and MVM, respectively. In both groups EtISO ranged between 0.6 and 1.8 %. A statistically significant difference between groups was found in cM only at T90 with a lower value in group MVM than MM (13.2 ± 3.0 vs 17.2 ± 3.4 ng ml-1; p = 0.024). The co-administration of vatinoxan in dogs premedicated with methadone and medetomidine may affect the plasma concentration of the opioid, although cardiovascular variables do not appear to present clinically relevant variations.