DISCREPANCY BETWEEN THE DEVELOPMENT OF TOLERANCE TO BUPIVACAINE IN EXTRADURAL AND SPINAL-ANESTHESIA IN RABBITS

We gave equal groups of rabbits seven extradural (500 mug kg-1) or int rathecal (250 mug kg-1) injections of bupivacaine, at 24-h intervals. A decrease in the duration of motor block was observed after the extra dural injections. The intrathecal injections exerted a reproducible ef fect. An additional regimen was tested in which five doses of bupivaca ine 125 mug kg-1 were administered intrathecally after a loading dose of 250 mug kg-1, when the animals showed partial recovery from the pre vious dose; there was no. decrease in the effect The absence of tolera nce to intrathecal bupivacaine implies that tachyphylaxis to extradura l local anaesthetics results from a decrease in availability of the dr ug to the neural target, rather than a diminution in effect at the sit e of action.