Comparison of bupivacaine carbonate and bupivacaine hydrochloride in epedural anesthesia in sheep

Abstract

Carbonated solutions of local anesthetic agents have been reported to exhibit shorter latency and more profound blockade than solutions of the hydrochloride salt. Using the sheep as a model for epidural anesthesia, we compared the carbonate and hydrochloride salts of bupivacaine, with and without epinephrine. Onsets and durations of analgesia and motor blockade were recorded, and plasma levels of drug were determined at various intervals after the epidural injections. Mean onset times were shorter with bupivacaine carbonate than with bupivacaine HCl and mean durations of analgesia were longer with the carbonated solutions, but these differences were not statistically significant. Peak plasma levels were higher with bupivacaine carbonate than with bupivacaine HCl, but the levels were quite low and none of the animals exhibited overt signs of systemic toxicity. Comparison of our results with those obtained in humans indicate the sheep is a reliable animal model for evaluating and comparing local anesthetic agents in epidural anesthesin.