RELATIVE NEURAL TOXICITY OF LOCAL-ANESTHETICS

In rat sciatic nerve, relative neural toxicity and relative motor nerv e conduction blockade were assessed for two amide-linked local anesthe tics (etidocaine and lidocaine) and two ester-linked local anesthetics (chloroprocaine and procaine). As measures of neural toxicity, nerve fiber injury and edema were assayed by light microscopic examination o f nerve tissue sampled 2 days after perineural (next to the sciatic ne rve) injection of various concentrations of the local anesthetics. Bot h nerve injury and edema increased with concentration of local anesthe tics, but injury was frequently present in nerve fascicles with little or no edema. In parallel studies, the amplitude of the electrical act ivity elicited from the interosseous muscles of the foot following ips ilateral electrical stimulation at the sciatic notch was monitored for up to 15 minutes to assess the extent of motor nerve blockade. The re sulting log concentration-response curves were analyzed for difference s in potency. Both for injury and for conduction block, the order of d ecreasing potency was: etidocaine, lidocaine, chloroprocaine, procaine . These results are not consistent with the proposal that ester-linked agents are more likely than other local anesthetic agents to cause ne rve injury.