Pharmacodynamics and plasma concentrations of dexmedetomidine with or without vatinoxan as a constant-rate infusion in horses anaesthetized with isoflurane-A pilot study.

The aim was to determine the effects of vatinoxan on dexmedetomidine plasma concentrations and effects on cardiovascular and intestinal tissue pharmacodynamics. In a prospective randomized study, six horses were premedicated intravenously with dexmedetomidine 3.5 µg kg-1 followed by a constant-rate infusion of 7 µg kg-1 h-1 (group DEX) and six horses with dexmedetomidine of the same dose (bolus and constant-rate infusion) combined with vatinoxan 130 µg kg-1 followed by 40 µg kg-1 h-1 (group VAT). Anaesthesia was induced with ketamine and diazepam and maintained with isoflurane. Venous blood samples were withdrawn before and at predefined points in time after drug application. During sedation and anaesthesia, cardiopulmonary variables, gastrointestinal tissue perfusion and oxygenation were recorded. Data were analysed using two-way-ANOVA, unpaired-t-test and Dunnett's-t-test (p < 0.05). Group VAT had significantly higher oxygen delivery and lower oxygen extraction ratio, venous admixture, alveolar dead space and alveolar-arterial-oxygen difference. Tissue perfusion of buccal mucosa was reduced during anaesthesia in group DEX. Plasma concentrations of dexmedetomidine in group VAT (n = 6) and group DEX (n = 5) were comparable between groups. In the present pilot study, co-administration of vatinoxan with dexmedetomidine did not alter plasma concentrations of dexmedetomidine but ameliorated tissue perfusion and global oxygenation variables.