EPIDURAL AND INTRATHECAL N-BUTYL-P-AMINOBENZOATE SOLUTION IN THE RAT - COMPARISON WITH BUPIVACAINE

Background Epidural administration of an aqueous suspension of n-butyl -p-aminobenzoate (BAB) to humans results in long-lasting sensory block ade without motor block. The dose-response of BAB administered epidura lly and intrathecally as a solution was studied in rats to define the local anesthetic properties in an established animal model. Methods: T he time course of changes in tail withdrawal latency and motor functio n were determined in rats after epidural or intrathecal administration of solutions of BAB or bupivacaine. The dose-response relation was de termined and median effective dose values were calculated. Results: Af ter epidural and intrathecal administration of BAB solutions, the onse t and duration of the antinociceptive action were comparable to bupiva caine. Median effective dose values for tail-withdrawal latency of 6 s or more were significantly greater for BAB. After both routes of admi nistration, BAB clearly affected motor function. Conclusions: When adm inistered epidurally and intrathecally as a solution, BAB is a local a nesthetic of relative low potency with onset and duration of action co mparable to those of bupivacaine. These findings suggest that the long -lasting action obtained after applying BAB suspension results from th e slow dissolution (continuous release) of the solid BAB deposited in the epidural space.