F02 - Pharmacokinetics of Lidocaine and its Metabolites Following Constant Rate Infusion in Healthy Goats

Abstract: Background – Continuous rate infusion (CRI) of lidocaine is commonly used as an analgesic in hospitalized goats, but no pharmacologic data is available in this species. The dosage used, often extrapolated from equine studies, might lead to suboptimal dosage and pain control in goats. Objectives – To determine the plasma concentrations achieved during a three-day administration of a CRI of lidocaine at 0.05 mg/kg/min in healthy goats. Animals – Eight healthy adult does from a teaching herd. Methods – Nine goats were enrolled for this clinical trial and were administered a CRI of lidocaine, intravenously, at 0.05 mg/kg/min for three consecutive days. Samples were collected before lidocaine administration, 0.25h, 0.5h, 1h, 3h, 6h, 12h, 24h, 36h, 48h, and 72h following the beginning of the CRI, and 0.25h, 0.5h, 1h, 3h, 6h, and 12h after discontinuation. Liquid chromatography tandem mass spectrometry was performed to determine serum concentration of lidocaine and its metabolites (OH-lidocaine, glycinexylidide, and monoethylglycinexylidide). Pharmacokinetic analysis was performed using non-compartment approach. Results – Transient self-limiting collapse was observed in three goats. Serum lidocaine concentrations reached a steady state 6 hours after starting the CRI. Mean maximal serum lidocaine concentration was 1425.2ng/mL (range 527.2–2930.8). Clearance was 4.2L/h/kg, with a terminal half-life of 1.4hours. Only OH-lidocaine was correlated to serum lidocaine concentration (P=0.01). Conclusions and Clinical Importance – Lidocaine metabolism is highly variable among healthy individuals, with some goats possibly requiring higher doses. Lidocaine as a CRI should not be administered to goat undiluted due to increased likelihood of adverse event.