Serum Concentrations of Lidocaine and Its Metabolites MEGX and GX During and After Prolonged Intravenous Infusion of Lidocaine in Horses after Colic Surgery

Abstract

Lidocaine is the most commonly used prokinetic after gastrointestinal surgery in horses. Cardiovascular status, hepatic function, and duration of therapy are the primary determinants of lidocaine metabolism, and these factors could affect equine patients after colic surgery. This study examined the systemic concentrations of lidocaine and its active metabolites monoethylglycinexylidide (MEGX) and glycinexylidide (GX), in horses that had undergone colic surgery and subsequently received prolonged postoperative lidocaine infusions. The mean lidocaine concentration increased over the course of treatment but did not exceed the therapeutic range. Concentrations of MEGX and GX increased progressively, and concentrations exceeding 1,000 ng/ml were observed frequently after 72 hours of infusion. None of the horses in the study developed severe signs of toxicity; however, the progressively increasing concentrations of lidocaine, MEGX, and GX are cause for concern in clinically ill patients receiving prolonged lidocaine therapy. The potential contribution of MEGX and GX should be considered when evaluating adverse reactions to prolonged lidocaine infusions.