Comparison of 2% mepivacaine and a solution of 2% lidocaine/epinephrine administered for median and ulnar nerve blocks in horses with naturally occurring forelimb lameness.

Objective: To compare a 2% lidocaine solution containing 5 μg/ml (1:200 000) epinephrine with 2% mepivacaine for reducing lameness in horses after use in proximal nerve blocks.

Study Design: Experimental randomized crossover.

Animals: Six adult horses with naturally occurring forelimb lameness.

Methods: Horses were evaluated using an inertial gait sensor system. Lameness was measured as a vector sum (VS). Following baseline lameness examination, median and ulnar nerve blocks were performed with lidocaine/epinephrine (0.5 mg epinephrine added to 50 ml of 2% lidocaine immediately prior to administration) or an equal volume of 2% mepivacaine. Horses were trotted at 5 min and then at 30 min intervals for 150 min. After 24 h, nerve blocks were repeated using the other local anesthetic. Data were evaluated using linear models.

Results: The reduction in the VS did not differ after nerve blocks with lidocaine/epinephrine or mepivacaine (P = .791). Mean time to VS <8.5 mm (n = 5) was 5 and 9.6 min for lidocaine/epinephrine and mepivacaine, respectively. For one horse, VS was not reduced to <8.5 mm with either treatment (this horse had the highest VS before treatments were administered). The decrease in VS to <8.5 mm lasted for 150 min in both treatment groups.

Conclusion: The outcomes of the median and ulnar nerve blocks performed with 2% lidocaine with epinephrine did not differ from blocks performed with 2% mepivacaine.

Clinical Relevance: Two percent lidocaine with epinephrine may serve as an adequate replacement for proximal nerve blocks when mepivacaine is unavailable.