EXPRESS: Pharmacokinetics of bupivacaine after bilateral maxillary and caudal inferior alveolar nerve blocks using two injection volumes in adult cats

Objectives This study described the pharmacokinetics of bupivacaine after bilateral maxillary and caudal inferior alveolar nerve blocks in adult cats under general anesthesia. Methods Ten healthy adult cats (4.8 ± 0.8 kg) were included in a randomized, prospective trial. Anesthetic protocol included acepromazine-methadone-propofol-isoflurane. Each cat randomly received 0.2 (BUPI2) or 0.3 mL (BUPI3) per site of bupivacaine 0.5% (4 and 6 mg per cat, respectively) (n = 5/group). Blood was collected before (time 0) and at 2, 7, 20, 30, 60, 120, 240, 360, 480 and 600 minutes after all dental blocks. Plasma concentrations of bupivacaine were analyzed using liquid chromatography-tandem mass spectrometry. The pharmacokinetics of bupivacaine were described using a non-compartmental analysis. Results Doses of bupivacaine were significantly different (BUPI2: 0.88 ± 0.14 mg/kg; BUPI3: 1.22 ± 0.21 mg/kg). For BUPI2 and BUPI3, maximum bupivacaine plasma concentrations (Cmax) were 825 ± 299 and 926 ± 197 ng/mL at 5.0 ± 2.7 and 9.6 ± 5.8 min (Tmax); area under the curve (AUC) to last measured concentration was 142 ± 36 and 180 ± 60 min*µg/mL; clearance was 5.2 (2) and 4.6 (13) mL/min/kg; elimination half-life was 245 ± 54 and 278 ± 90 min and mean residence time to the last measured concentration was 185 (32) and 196 (76) min, respectively. Concentrations of bupivacaine were detected up to 600 minutes (72 ± 22 in BUPI2 and 104 ± 55 ng/mL in BUPI3). Conclusions and relevance Bilateral maxillary and caudal inferior alveolar nerve blocks using two volumes and doses of administration produced Cmax below those reported to cause toxicity in cats. Further studies are warranted to investigate the pharmacodynamics of dental blocks in cats.