文摘
Local anesthetics are useful for reducing acute pain, but their short duration precludes them fromuse in solely managing postoperative pain. To prolong the duration of local anesthesia, we conjugatedbupivacaine to native hyaluronan (HA) and divinyl sulfone cross-linked Hylan A (Hylan B particles)using a hydrolyzable linker incorporating an imide. Bupivacaine was prepared for conjugation to HAby forming the acryl imide derivative. Separately, the carboxyl group of HA was reacted withnipsylethylamine (NEA) using carbodiimide-mediated coupling to provide HA-NEA that wassubsequently reduced with tris(2-carboxyethylphosphine) hydrochloride to yield HA carrying a freesulfhydryl (HA-SH). The HA-bupivacaine conjugate was assembled by reacting HA-SH withacrylbupivacaine. Characterization of the conjugates showed 22% degree of modification by 1 mol ofcarboxyl. In vitro release studies comparing bupivacaine admixed in HA with bupivacaine conjugatedto HA showed half-lives of 0.4 ± 0.1 h, and 16.9 ± 0.2 h, respectively, and the bupivacaine was releasedchemically unaltered as confirmed by LC-MS. In vivo studies to assess the duration of anestheticactivity were performed in a rat sciatic nerve blockade model. For these studies, bupivacaine wasconjugated to Hylan B following a similar procedure, and the degree of modification obtained was14%. Free bupivacaine (3 and 16 mg/kg) and free bupivacaine (3 mg/kg) admixed with Hylan B particlesshowed nerve block over 4, 9, and 6 h, respectively. Free bupivacaine (3 mg/kg) admixed withbupivacaine (13 mg/kg) conjugated to Hylan B particles showed a four to 5-fold longer impairment ofmotor function over the free bupivacaine formulations with a total block time of 19 h. Bupivacaineconjugated to Hylan B particles has the potential to prolong the duration of local anesthesia.
