The aim of this study was to gain insight into the pharmacokinetics and cardiovascular response to perineural administration of dexmedetomidine (DEX) and levobupivacaine (LB) and to determine whether DEX limits the perioperative stress response. Forty dogs undergoing dental procedure under general anaesthesia with isoflurane were administered 0.5% LB to both infraorbital (IO) blocks (0.11 mL/kg2/3) and both inferior alveolar (IA) blocks (0.18 mL/kg2/3). In addition to LB, 10 dogs were administered DEX (0.5 µg/kg) perineurally at IO nerve (LB + DEX IO), ten dogs at IA nerve (LB + DEX IA), and 10 dogs were administered DEX intravenously (LB + DEX IV). Ten dogs were administered a placebo intravenously (LB + PLC IV). Blood was collected to determine the concentration of LB and DEX using the LC-MS /MS analysis before and after administration of the two drugs and also at 1, 2, 5, 10, 15, 30, 45, 60, 90, and 120 minutes thereafter. Cardiovascular parameters were measured every minute for the first 12 minutes and then every five minutes until the end of the procedure. Blood was drawn to determine cortisol and glucose concentrations after the induction of general anaesthesia and at the end of the procedure. Twenty additional dogs were included in the study and applied LB to only one site (IO or IA block). For the determination of LB, blood was collected at the same time points as in the first part of the study. The absorption of DEX was non-significantly faster in the LB + DEX IO group, whereas in the LB + DEX IA group, better bioavailability (56% vs. 48%) and faster elimination were observed. Heart rate was significantly lower in all groups of dogs receiving DEX compared to the placebo group. Mean arterial pressure was significantly higher in the LB + DEX IV and LB + DEX IA groups compared to the LB + PLC IV group. Cortisol concentration was non-significantly lower at the end of the procedure in all groups, and glucose concentration was significantly lower at the end of the procedure only in the LB + DEX IA group. Only the stomatologist, but not the anaesthesiologist and the dog owner, determined a significantly lower level of pain 14 days after the procedure. The fastest absorption of LB occurred after administration near the IA nerve (LB IA). The site of perineural application of DEX and LB did not affect the rate and amount of systemic absorption, and DEX did not limit the perioperative stress response, probably because of the low dose we used.
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