ON THE RELATIVE POTENCY OF AMINO-AMIDE LOCAL-ANESTHETICS IN-VIVO

With the aim of comparing the analgesic effectiveness of lidocaine, pr ilocaine, bupivacaine and etidocaine in vivo, a study of the relations hips between dose and duration of infraorbital nerve block (IONB) of v arious intensities (IONB degrees 3-10) was performed in the rat. With increasing doses longer durations of action were obtained. Further ana lyses were performed using multiple regression analysis. The log (dose ) - duration lines for bupivacaine and etidocaine were found to be lin ear, whereas those for lidocaine in degree 3 and degree 10 IONB and fo r prilocaine in degree la IONB were so only after omission of some dat a. The only comparisons yielding no deviation from parallelism of log (dose) - duration lines were etidocaine vs. lidocaine at IONB degree 1 0 and lidocaine vs. prilocaine and bupivacaine vs, etidocaine at IONB degree 3. The difference between these agents with respect to their du ration of action at all dose levels amounted to 11 +/- 3 minutes (M+/- s.e.m.) for etidocaine vs lidocaine (IONB degree 10), 27 +/- 4 min for prilocaine vs. lidocaine and 54 +/- 5 min for bupivacaine vs. etidoca ine (IONB degree 3). For all other comparisons the log (dose) - durati on lines deviated from parallelism, i.e. differences between agents wi th respect to their duration of action were found to be dose-dependent . The slopes of the log (dose) - duration lines were found to correlat e closely to the log (partition coefficient) and log (protein binding) of the investigated agents.