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

Abstract

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 epidural space at the level of L6-7 in each animal. A solution 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 injected 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 and motor block of 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 micro gram/mL) in Group I. In Group II, the level reached a maximum 30 min aftter injection (3.7 +/- 1.5 micro gram/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 system for local anesthetics. (Anesth Analg 1995;80:97-101)