Duration of action of mepivacaine and lidocaine in equine palmar digital perineural blocks in an experimental lameness model.
Authors: Hoerdemann Mona, Smith Rachael L, Hosgood Giselle
Journal: Veterinary surgery : VS
Summary
# Editorial Summary Eight horses with experimentally induced forelimb lameness received palmar digital nerve blocks using either 2% mepivacaine or 2% lidocaine in a crossover design, with lameness quantified via inertial sensor and skin sensitivity assessed by force gauge. Mepivacaine proved markedly superior: it resolved lameness in all eight horses compared to only three with lidocaine, and maintained analgesia substantially longer (mean duration 366 minutes versus 113 minutes for lameness resolution; 195 versus 63 minutes for skin sensitivity recovery). A critical finding emerged regarding diagnostic use—skin desensitization occurred independently of lameness resolution, particularly with lidocaine where sensation returned whilst lameness persisted, meaning practitioners cannot reliably interpret skin sensitivity as a proxy for effective analgesia or nerve block duration. For equine practitioners using palmar digital blocks for both diagnostic and therapeutic purposes, mepivacaine offers significantly greater reliability and longer-lasting effect, whilst lidocaine's poor lameness resolution rate warrants reconsideration in clinical decision-making; additionally, relying on simple skin palpation to confirm block effectiveness or predict duration may lead to premature case dismissal or inadequate pain control.
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Practical Takeaways
- •Use mepivacaine instead of lidocaine for palmar digital nerve blocks in diagnostic lameness work—lidocaine fails to resolve lameness in ~60% of cases despite apparent desensitization
- •Do not rely on return of skin sensation to assess when a palmar digital block is wearing off; mepivacaine analgesia lasts ~3 hours but lidocaine only ~2 hours, yet skin sensation returns at different rates
- •When performing diagnostic nerve blocks, understand that the horse may still be lame despite losing skin sensation—use objective lameness assessment (sensors, gait evaluation) rather than skin prick tests alone
Key Findings
- •Mepivacaine resolved lameness in 8/8 horses versus only 3/8 horses with lidocaine despite both causing skin desensitization
- •Mepivacaine provided significantly longer duration of action: 366 minutes for lameness resolution compared to 113 minutes for lidocaine (P=0.038)
- •Skin sensitivity returned sooner than lameness relief after lidocaine blocks, making skin sensation an unreliable indicator of anesthetic effectiveness for this drug
- •Skin desensitization occurred before lameness resolution with mepivacaine, indicating these two effects have different onset kinetics