Spinal anesthesia: significant prolongation of the pharmacologic effect of tetracaine with lipid solution of the agent.

A novel approach for increasing the duration of anesthesia after a single subarachnoid injection of a local anesthetic is presented. Tetracaine 1% 0.5 mg/kg was administered in 10% glucose or in lipid solution (iophendylate) in two groups of rabbits via catheters chronically implanted in the subarachnoid space. The pharmacologic effect was assessed by evaluation of the intensity and duration of the motor blockade according to a three-stage scale. Significant prolongation (447 +/- 13 min vs. 130 +/- 7 min, P less than 0.01) with a moderate decrease in the intensity of the motor blockade was observed with lipid solution as compared to the aqueous solution. This effect is attributed to the slow release of the agent from the lipid phase, which actually functions as a drug depot in the cerebrospinal fluid. The proposed method is suggested as an additional approach for the development of drug delivery system intended for prolongation of spinal anesthesia.