Prolongation of Epidural Anesthesia in the Rabbit with the Use of a Biodegradable Copolymer Paste Containing Lidocaine

MD* Departments of *Anesthesiology and SClinical Pharmacy, Institute of Clinical Medicine, University of Tsukuba, and tDepartment of Pharmacy, University Hospital of Tsukuba, Tsukuba, Ibaraki, Japan Prolongation of the drug effect using a drug-delivery system has recently been introduced in local anesthesia. In this study, we investigated the prolonging effect of an epidurally injected biodegradable copolymer paste containing 10% lidocaine (Lid-CoPol). Twenty-nine rabbits were studied. A catheter was placed in the epi- dural space at the level of L6-7 in each animal. A solu- tion of 10% lidocaine (Group I, n = 12), or a copolymer containing 10% lidocaine (Lid-CoPol), (Group II, n = 12) or copolymer paste only (Group III, n = 5) was in- jected epidurally at a dose of 0.15 mL/kg. The effect of each drug was assessed by evaluation of response to pain stimulation and of the degree of motor block produced. The plasma lidocaine concentration was also measured consecutively in five animals of both Groups I and II. The duration of sensory motor block Lid-CoPol was 800% and 975% longer, respectively, than that of plain lidocaine solution. Plasma lidocaine concentration reached a maximum 5 min after injection (5.5 ? 0.5 pg/mL) in Group I. In Group II, the level reached a maximum 30 min aftter injection (3.7 ? 1.5 pg/mL). The findings are attributed in part to the slow release of lidocaine from the biodegradable copolymer paste, which is suggested as a new drug-delivery sys- tem for local anesthetics. (Anesth Analg 1995;80:97-101)