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

ObjectivesThis study described the pharmacokinetics of bupivacaine after bilateral maxillary and caudal inferior alveolar nerve blocks in adult cats under general anaesthesia.MethodsA total of 10 healthy adult cats (mean ± SD weight 4.8 ± 0.8 kg) were included in a randomised, prospective trial. The anaesthetic protocol consisted of acepromazine-methadone-propofol-isoflurane. Each cat randomly received 0.2 (BUPI2) or 0.3 ml (BUPI3) of bupivacaine 0.5% per site (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 mins after all dental blocks. Plasma concentrations of bupivacaine were analysed using liquid chromatography-tandem mass spectrometry. The pharmacokinetics of bupivacaine were described using a non-compartmental analysis.ResultsMean doses of bupivacaine were significantly different (BUPI2: 0.88 ± 0.14 mg/kg; BUPI3: 1.22 ± 0.21 mg/kg). For BUPI2 and BUPI3, mean maximum bupivacaine plasma concentrations (Cmax) were 825 ± 299 and 926 ± 197 ng/ml at 5.0 ± 2.7 and 9.6 ± 5.8 mins (time to peak concentration); mean area under the curve to the last measured concentration was 142 ± 36 and 180 ± 60 min*µg/ml; mean clearance was 5.4 ± 0.8 and 7 ± 5.7 ml/min/kg; mean elimination half-life was 245 ± 54 and 278 ± 90 mins; and mean residence time to the last measured concentration was 185 ± 13 and 182 ± 33 mins, respectively. Concentrations of bupivacaine were detected up to 600 mins (72 ± 22 ng/ml in BUPI2 and 104 ± 55 ng/ml in BUPI3).Conclusions and relevanceBilateral 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.