Perineural dexamethasone does not prolong bupivacaine sensory blockade in equine palmar digital nerve blocks: a randomized crossover trial.

Perineural dexamethasone SP does not prolong bupivacaine nerve blocks in horses and may shorten duration.

This blinded, randomized 4×4 crossover trial investigated whether adding dexamethasone sodium phosphate (dexamethasone SP) to bupivacaine prolongs sensory blockade in equine palmar digital nerve blocks. Eight healthy adult horses received four perineural treatments—bupivacaine alone, bupivacaine combined with dexamethasone SP, dexamethasone SP alone, or saline—over the palmar digital nerves of the left forelimb, with a minimum 7-day washout between treatments. Mechanical nociceptive threshold (MNT) was measured at baseline and at prespecified intervals for up to 12 hours, with blockade duration defined as the period MNT remained at the maximum measurable value (3.5 kg/cm²). Both bupivacaine alone and the bupivacaine–dexamethasone SP combination significantly elevated MNT compared to saline and dexamethasone SP alone. Dexamethasone SP alone produced no measurable analgesic effect. Contrary to the study hypothesis—and to established human and murine data—the addition of dexamethasone SP did not prolong bupivacaine-induced blockade. Notably, median blockade duration was shorter for the combination (2.5 hours) than for bupivacaine alone (4.5 hours), suggesting dexamethasone SP may actually reduce duration. No local or systemic adverse effects were observed. These findings reveal a significant interspecies difference and indicate that extrapolation of human adjuvant protocols to equine patients is not appropriate. Further investigation into pharmacologic interactions and species-specific mechanisms is warranted before incorporating perineural dexamethasone into equine regional analgesia protocols.

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