Formation and Characterization of Carbopol 971P-PVP Interpolymer complex and its application for sustained delivery of Acyclovir

INTRODUCTION Polymers are the substances of high molecular weight with repeating monomer units widely used in pharmaceutical systems. The chemical reactivity of polymers depends upon chemical nature of their monomer units, but their properties depend upon the way the monomers are put together.[1] Modifications of polymers and their properties is an important technological problem. For realization of this problem, some scientific principles for polymer modification are necessary. The change of structural organization of polymer systems can be used as indicator of polymer modification. The ways to perform polymer modification include interpolymer complexes, protein-polymer conjugates, macromolecular metal complexes and complexes of polymers with low molecular weight compounds.[2] However, use of interpolymer complexation method has wide applications in case of pharmaceutical delivery systems. These include mucoadhesive systems using poly (acrylic acid),[3-5] poloxamer,[4] Poly (vinyl) pyrrolidone;[6] complexation hydrogels using poly(methacrylic acid grafted with poly(ethylene glycol)), (P(MAA-g-EG));[7] controlled drug release;[8,9] nanoparticulates;[10] in situ gelling systems [11] etc. In particular, use of Carbopol as mucoadhesive polymer is widely accepted. It was used in various interpolymer polymer complexes for controlling drug release.[9-12] Poly(vinyl pyrrolidone) (PVP) was used by Gonjari et al.[13] as mucoadhesive polymer for ophthalmic gels. PVP was used for complexation with various other polymers. Chun et al.[14] studied complexation of PVP and poly (acrylic acid). In another study, PVP was complexed with poly vinyl acetate phthalate.[15] Complexation between polymers can be studied by measurement of turbidity, pH, and ionic strength as the function of weight ratio of polymer in media, Research Article