ENHANCEMENT OF BUPIVACAINE SENSORY BLOCKADE OF RAT SCIATIC-NERVE BY COMBINATION WITH PHENOL

We sought to determine whether the addition of phenol would enhance a bupivacaine nerve block. The effects on nerve conduction of bupivacain e (0.125%) and phenol (0.5%), singly and combined, were evaluated in v ivo on the rat sciatic nerve. Three groups of 10 animals each were use d. The left sciatic nerve was infiltrated with 0.125% bupivacaine, 0.5 % phenol, or a solution that contained 0.125% bupivacaine and 0.5% phe nol. The right limb served as control (saline injected). Motor deficit s (visual assessment) and sensory blockade (hot-plate assay) were eval uated at 30-min intervals after injection. Phenol injected alone produ ced no motor blockade. The incidence of motor blockade at 30 min for 0 .125% bupivacaine was 70% (P = 0.003), and for the combination treatme nt, 80% (P = 0.001). The analgesia score derived from the hot-plate te st was more and persisted longer for the combination treatment than fo r either 0.125% bupivacaine or 0.5% phenol given singly; e.g., the ave rage sensory block score after 150 min for the combination treatment w as 1.0 compared with 0.1 for either bupivacaine or phenol given alone (P = 0.003). Analysis of the areas under the sensory score-time curves also demonstrated enhanced blockade from the combination treatment, w hich would be consistent with a synergism of the separate Na+-channel blocking effects of charged and uncharged local anesthetics. These fin dings may suggest other candidates for clinically useful combinations of amine and neutral local anesthetics.