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

Objective: To determine whether dexamethasone sodium phosphate (dexamethasone SP) prolongs the sensory blockade produced by perineural bupivacaine during medial and lateral palmar digital nerve blocks in horses. Methods: 8 healthy adult horses were enrolled in a blinded, randomized 4 X 4 crossover trial. Each horse received 1 of 4 perineural treatments over the palmar digital nerves of the left forelimb: bupivacaine, bupivacaine + dexamethasone SP, dexamethasone SP alone, or saline. A minimum 7-day washout was used between treatments. Mechanical nociceptive threshold (MNT) was measured at baseline and at prespecified intervals for up to 12 hours. Duration of sensory blockade was defined as the time during which MNT remained at the maximal measurable value (3.5 kg/cm2). Time-to-event analyses were performed using Kaplan-Meier curves and Gehan-Breslow-Wilcoxon tests (α = 0.05). Results: Bupivacaine and bupivacaine + dexamethasone SP both increased MNT relative to saline and dexamethasone SP alone (P < .05). Dexamethasone SP alone had no detectable effect on MNT. Contrary to the study hypothesis, the addition of dexamethasone SP did not prolong bupivacaine's duration of sensory blockade. Median duration was 4.5 hours for bupivacaine alone and 2.5 hours for bupivacaine + dexamethasone SP. No adverse local or systemic effects occurred. Conclusions: Perineural dexamethasone SP did not enhance, and may reduce, the duration of sensory blockade produced by bupivacaine in palmar digital nerve blocks in healthy horses. These findings warrant further investigation into potential pharmacologic interactions and clinical implications for equine analgesic protocols. Clinical Relevance: Contrary to strong translational clinical data, the addition of dexamethasone does not prolong the duration of nerve blocks in horses. These findings highlight a clear interspecies difference and suggest that the effect seen in human and murine models does not correlate to the effect in equids.