Prolongation of epidural anesthesia using a lipid drug carrier with procaine, lidocaine, and tetracaine.

This study evaluated the effect of a lipid drug carrier (iophendylate) on epidural anesthesia. The intensity and duration of motor blockade produced by aqueous and lipid preparations of local anesthetics were assessed in rabbits with long-term indwelling catheters in the epidural space. Motor blockades produced by procaine (1%, 2%, and 4%), lidocaine (1%, 2%, and 4%), and tetracaine (0.5%, 1%, and 2%) in normal saline solution were compared with the effects produced by equimolar amounts of the drug solutions in iophendylate. Procaine (4%) in aqueous solution produced motor blockade lasting 30 +/- 3.54 min (mean +/- SD) versus 84 +/- 4.18 min in lipid solution. Lidocaine (2% and 4%) in aqueous solution produced motor blockade lasting 41 +/- 4.18 and 65 +/- 6.12 min versus 39 +/- 4.18 and 118 +/- 10.1 min, respectively, in lipid solution. Aqueous tetracaine (0.5%, 1%, and 2%) produced motor blockade of 106 +/- 9.62, 189 +/- 6.52, and 273 +/- 26.8 min versus 284 +/- 14.7, 335 +/- 15.8, and 365 +/- 26.9 min, respectively, in their lipid counterparts. A control group of animals that received normal saline solution or iophendylate alone did not exhibit motor blockade. These results may be attributed to sustained release of local anesthetics from the lipid vehicle. Hence, lipid drug carriers may be effective in prolonging epidural anesthesia.