Pharmacokinetics and metabolism of lidocaine HCl 2% with epinephrine in horses following a palmar digital nerve block.
Authors: Knych Heather K, Katzman Scott, McKemie Daniel S, Arthur Rick M, Blea Jeff
Journal: BMC veterinary research
Summary
# Editorial Summary Lidocaine with epinephrine is routinely used for palmar digital nerve blocks in horses, yet regulatory concerns about masking lameness in performance animals have created a need for detailed pharmacokinetic data on this combination. Knych and colleagues administered a standard 20 mg dose of 2% lidocaine with 1:100,000 epinephrine as a palmar digital nerve block to twelve horses, then tracked serum and urinary concentrations of lidocaine and its metabolites (MEGX and GX) over 30 and 48 hours respectively using liquid chromatography-mass spectrometry, followed by both compartmental and non-compartmental pharmacokinetic analysis. The epinephrine component successfully prolonged lidocaine residence time at the injection site by reducing systemic absorption, with detectable serum concentrations persisting beyond 24 hours in most horses—information critical for establishing appropriate competition withdrawal periods and understanding individual variation in local anesthetic duration. These findings provide the evidence base regulators and practitioners need to set science-backed guidelines, whilst helping clinicians interpret why some horses may metabolise or absorb the drug differently and thus experience variable analgesia duration during diagnostic lameness work.
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Practical Takeaways
- •Understanding lidocaine pharmacokinetics with epinephrine is critical for practitioners administering blocks to performance/racehorses, as detection windows affect regulatory compliance and eligibility to compete
- •Palmar digital nerve blocks with epinephrine provide prolonged anesthetic effect locally while minimizing systemic absorption, supporting longer lameness masking duration—important for post-procedure protocols
- •Blood and urine detection protocols based on this data can help establish safe administration timing before competitions with regulatory testing
Key Findings
- •Lidocaine 2% with epinephrine (20 mg/horse) administered as palmar digital nerve block was detected in serum for up to 30 hours post-administration
- •Primary metabolites of lidocaine were quantified in serum and urine, with urine elimination continuing up to 48 hours
- •Pharmacokinetic analysis characterized serum and urine concentrations to establish baseline data for regulatory compliance in racehorses
- •Addition of epinephrine 1:100,000 prolonged local anesthetic duration at injection site by reducing systemic absorption