MK-467 accelerated the absorption of IM coadministered drugs. This is clinically relevant as it may hasten the onset of peak sedative effects.

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OBJECTIVE To investigate the cardiovascular and sedation reversal effects of IM administration of atipamezole (AA) in dogs treated with medetomidine hydrochloride (MED) or MED and vatinoxan (MK-467). ANIMALS 8 purpose-bred, 2-year-old Beagles. PROCEDURES A randomized, blinded, crossover study was performed in which each dog received 2 IM treatments at a ≥ 2-week interval as follows: injection of MED (20 μg/kg) or MED mixed with 400 μg of vatinoxan/kg (MEDVAT) 30 minutes before AA (100 μg/kg). Sedation score, heart rate, mean arterial and central venous blood pressures, and cardiac output were recorded before and at various time points (up to 90 minutes) after AA. Cardiac and systemic vascular resistance indices were calculated. Venous blood samples were collected at intervals until 210 minutes after AA for drug concentration analysis. RESULTS Heart rate following MED administration was lower, compared with findings after MEDVAT administration, prior to and at ≥ 10 minutes after AA. Mean arterial blood pressure was lower with MEDVAT than with MED at 5 minutes after AA, when its nadir was detected. Overall, cardiac index was higher and systemic vascular resistance index lower, indicating better cardiovascular function, in MEDVAT-atipamezole–treated dogs. Plasma dexmedetomidine concentrations were lower and recoveries from sedation were faster and more complete after MEDVAT treatment with AA than after MED treatment with AA. CONCLUSIONS AND CLINICAL RELEVANCE Atipamezole failed to restore heart rate and cardiac index in medetomidine-sedated dogs, and relapses into sedation were observed. Coadministration of vatinoxan with MED helped to maintain hemodynamic function and hastened the recovery from sedation after AA in dogs.

Objective To investigate the impact of intramuscular (IM) co-administration of the peripheral a 2 -adrenoceptor agonist vatinoxan (MK-467) with medetomidine and butorphanol prior to intravenous (IV) ketamine on the cardiopulmonary and anaesthetic effects in dogs, followed by atipamezole reversal.Study design Randomized, masked crossover study.Animals A total of eight purpose-bred Beagle dogs aged 3 years.Methods Each dog was instrumented and administered two treatments 2 weeks apart: medetomidine (20 mg kg e1 ) and butorphanol (100 mg kg e1 ) premedication with vatinoxan (500 mg kg e1 ; treatment MVB) or without vatinoxan (treatment MB) IM 20 minutes before IV ketamine (4 mg kg e1 ). Atipamezole (100 mg kg e1 ) was administered IM 60 minutes after ketamine. Heart rate (HR), mean arterial (MAP) and central venous (CVP) pressures and cardiac output (CO) were measured; cardiac (CI) and systemic vascular resistance (SVRI) indices were calculated before and 10 minutes after MVB or MB, and 10, 25, 40, 55, 70 and 100 minutes after ketamine. Data were analysed with repeated measures analysis of covariance models. A p-value <0.05 was considered statistically significant. Sedation, induction, intubation and recovery scores were assessed.Results At most time points, HR and CI were significantly higher, and SVRI and CVP significantly lower with MVB than with MB. With both treatments, SVRI and MAP decreased after ketamine, whereas HR and CI increased.MAP was significantly lower with MVB than with MB; mild hypotension (57e59 mmHg) was recorded in two dogs with MVB prior to atipamezole administration. Sedation, induction, intubation and recovery scores were not different between treatments, but intolerance to the endotracheal tube was observed earlier with MVB.Conclusions and clinical relevance Haemodynamic performance was improved by vatinoxan co-administration with medetomidineebutorphanol, before and after ketamine administration. However, vatinoxan was associated with mild hypotension after ketamine with the dose used in this study. Vatinoxan shortened the duration of anaesthesia.