Serum concentrations of lidocaine and its metabolites after prolonged infusion in healthy horses.
Authors: Dickey E J, McKenzie H C, Brown K A, de Solis C N
Journal: Equine veterinary journal
Summary
# Editorial Summary Prolonged continuous-rate infusions (CRI) of lidocaine are commonly used in equine practice for analgesia and anti-inflammatory effects, yet pharmacokinetic data beyond 24 hours had been limited. Dickey and colleagues administered lidocaine at 0.05 mg/kg bodyweight per minute to eight healthy horses for 96 hours, measuring serum concentrations of the parent drug and its active metabolites glycinexylidide (GX) and monoethylglycinexylidide (MEGX) using high-performance liquid chromatography at multiple timepoints during and after infusion. Lidocaine reached steady state rapidly (by 3 hours) without accumulation, remaining mostly within therapeutic range (980 ng/ml), whilst MEGX also showed no accumulation; however, GX accumulated substantially over the first 48 hours before plateauing, raising concern given its potential neurotoxicity. Despite this metabolite accumulation, no clinical signs of toxicity were observed in any horse, and all measured compounds cleared to undetectable levels within 24 hours of discontinuing the infusion. These findings suggest that 96-hour lidocaine CRI at this dose is safe in systemically healthy horses, though the significant GX accumulation warrants caution in patients with hepatic or renal compromise, and longer-term safety data in compromised animals remains advisable before extending infusion protocols beyond 96 hours.
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Practical Takeaways
- •96-hour lidocaine infusions at 0.05 mg/kg/min appear safe in healthy horses with no observed toxicity signs, despite GX accumulation up to 48 hours
- •Hepatic metabolism of lidocaine remains adequate even with prolonged infusion, allowing safe use for extended pain management or perioperative applications
- •Monitor horses receiving prolonged lidocaine infusions for GX-related toxicity signs, particularly around 24-48 hours when metabolite accumulation peaks
Key Findings
- •Serum lidocaine reached steady state by 3 hours and did not accumulate during 96-hour continuous infusion at 0.05 mg/kg/min
- •Glycinexylidide (GX) accumulated significantly up to 48 hours then remained constant, while monoethylglycinexylidide (MEGX) did not accumulate
- •Lidocaine concentrations remained below potentially toxic levels (>1850 ng/ml) throughout the 96-hour infusion period
- •All serum concentrations of lidocaine, MEGX, and GX were undetectable within 24 hours of infusion discontinuation