Delivery of bupivacaine included in poly(acrylamide-co-monomethyl itaconate) hydrogels as a function of the pH swelling medium

Copolymeric hydrogels of poly(acrylamide-co-monomethyl itaconate) (A/MMI) crosslinked with N,N'-methylenbisacrylamide (NBA) were synthesized as devices for the controlled release of bupivacaine (Bp). Two compositions of the copolymer, 60A/40MMI and 75A/25MMI, were studied. A local anesthetic was included in the feed mixture of polymerization (2-8 mg Bp/tablet) and by immersion of the copolymeric tablets in an aqueous solution of the drug. A very large amount of Bp (36-38 mg Bp/tablet) was included in the gels by sorption due to interactions between the drug and the side groups of the hydrogels. Swelling and drug release were in accordance with the second Fick's law at the first stages of the processes. The swelling behavior of these copolymers depended on the pH of the medium. The equilibrium swelling degree (W-infinity) was larger at pH 7.5 (W-infinity approximate to 90 wt %) than at pH 1.5 (W-infinity approximate to 52-64 wt %) due to the ionization of the side groups of the copolymer. Release of the drug also depended on the pH of the swelling medium; at pH 7.5, about 60% of the included drug was released, and at pH 1.5, about 80% was released. Bp release was controlled by the comonomer composition of the gels, their drug-load, and the pH of the swelling medium. (C) 2002 Wiley Periodicals, Inc.