Abstract

The effect of fentanyl, meperidine and diamorphine on A- and C-fiber conduction in an in vitro rabbit vagus nerve preparation was examined. The nerves were maintained at 37°C with an oxygenated electrolyte solution. The effect of the commercial preparation of fentanyl (Sublimaze) and isotonic solutions of fentanyl, meperidine and diamorphine were observed. Sublimaze had a neurotoxic effect related to its hypotonicity. In isotonic solutions, fentanyl and meperidine, but not diamorphine, blocked nerve conduction and both showed marked frequency-dependent blocking actions in C-fibers. Naloxone (Narcan) did not prevent the effect of fentanyl. Both fentanyl and meperidine potentiated the block produced by a low concentration of bupivacaine (0.005 mM, 0.00016%), the effect of meperidine being seen at clinically relevant concentrations. Fentanyl was slightly more potent than meperidine in its effect on nerve conduction, but its greater opioid potency would not allow its use as a local anesthetic. The local anesthetic effect of meperidine may be more useful clinically.