Effects of intravenous lidocaine overdose on cardiac electrical activity and blood pressure in the horse

Abstract

Summary This study aimed to identify blood serum lidocaine concentrations in the horse which resulted in clinical signs of intoxication, and to document the effects of toxic levels on the cardiovascular and cardiopulmonary systems. Nineteen clinically normal mature horses of mixed breed, age and sex were observed. Lidocaine administration was initiated in each subject with an i.v. loading dose of 1.5 mg/kg bwt and followed by continuous infusion of 0.3 mg/kg bwt/min until clinical signs of intoxication were observed. Intoxication was defined as the development of skeletal muscle tremors. Prior to administration of lidocaine, blood samples for lidocaine analysis, heart rate, mean arterial blood pressure, systolic blood pressure, diastolic blood pressure, respiratory rate and electrocardiographic (ECG) data were collected. After recording baseline data, repeat data were collected at 5 min intervals until signs of intoxication were observed. The range of serum lidocaine concentrations at which the clinical signs of intoxication were observed was 1.85–4.53 μg/ml (mean ± s.d. 3.24 ± 0.74 μg/ml). Statistically significant changes in P wave duration, P‐R interval, R‐R interval and Q‐T interval were observed in comparison to control values, as a result of lidocaine administration. These changes in ECG values did not fall outside published normal values and were not clinically significant. Heart rate, blood pressures and respiratory rates were unchanged from control values. This study establishes toxic serum lidocaine levels in the horse, and demonstrates that there were no clinically significant cardiovascular effects with serum lidocaine concentrations less than those required to produce signs of toxicity.

Serum concentrations of lidocaine and its metabolites after prolonged infusion in healthy horses

“…The target steady state concentration for the treatment of ileus in the horse is 980ng/ml (1000-2000ng/ml range), (Malone et al 1998) and the serum lidocaine concentrations resulting in adverse side effects have been reported to be >1850ng/ml. (Meyer et al 2001) In that study the investigators did not note any cardiovascular anomalies, however behavioral abnormalities were observed at a serum concentration of 1.85-4.35ug/ml (mean 3.24+/-740ug/ml). In human patients subjective side effects are reported at lidocaine concentrations above 3-5ug/ml and objective toxicities observed above 6-10ug/ml.…”

“…In only one instance did this occur in temporal proximity to a sample collection, and this sample was not included in the analysis. Conversely, serum lidocaine concentrations did not at any time point reach concentrations in the range described as potentially toxic (>1850ng/ml) (Brianceau et al 2002;Malone et al 2006;Meyer et al 2001).…”

“…The signs of lidocaine toxicity reported in the horse include alteration in visual function, rapid eye blinking, anxiety, mild sedation, ataxia and collapse. (Brianceau et al 2002;Malone et al 2006;Meyer et al 2001) Equine colic patients at the investigator's clinic (MDSEMC) that were receiving prolonged lidocaine infusions have been observed to develop ataxia, muscle tremors and altered mentation, raising concern that toxic levels may have been reached despite the use of the recommended dosage regimen. The target steady state concentration for the treatment of ileus in the horse is 980ng/ml (1000-2000ng/ml range), (Malone et al 1998) and the serum lidocaine concentrations resulting in adverse side effects have been reported to be >1850ng/ml.…”

Effects of the morphine-lidocaine-ketamine combination on cardiopulmonary function and isoflurane sparing in sheep

“…Alterations in behavior, which include visual dysfunction, anxiety and ataxia, were observed after overdosing with lidocaine at plasma concentrations of 1850-4530 ng/mL in horses (MEYER et al, 2001). Tremors and signs similar to visual dysfunction, including staring and inspecting the walls and floor were observed in some of the horses that received the same dose of lidocaine used in the present study (VALVERDE et al, 2005).…”

Antinociceptive effects of three escalating dexmedetomidine and lignocaine constant rate infusions in conscious horses

“…The pharmacokinetic profiles following lignocaine infusions in conscious and anaesthetised horses have been determined (Feary et al, 2005(Feary et al, , 2006, and the plasma concentrations for reducing the minimal alveolar concentration of inhalational anaesthetics, as well as plasma concentrations producing toxic side effects in conscious horses, are known (Meyer et al, 2001;Waxman et al, 2012). However, the minimum infusion rate and corresponding plasma concentrations of lignocaine necessary to provide antinociception in conscious horses have not been described.…”