Roles of acid/base nature and molecular weight in drug release from matrices of gelfoam and monoisopropyl ester of poly(vinyl methyl ether maleic anhydride)

Ophthalmic drug inserts are usually placed in the conjunctival sac. Being i n contact with the conjunctiva, they may provide means to deliver large and hydrophilic molecules, such as peptides and oligonucleotides into the eye. We evaluated Gelfoam and monoisopropyl ester of poly(vinyl methyl ether/ma leic anhydride) (PVM/MA) as potential polymers for ocular inserts, Matrices were solvent cast with model drugs that had different pK(a), molecular wei ght and hydrophilicity. Drug release from the matrices as well as charge an d swelling of Gelfoam(R)-matrix were studied. The release of drugs from PVM /MA-matrices was by erosion of thee polymer matrix. The molecular weight an d other variants of the releasing compound did not affect their release. In Gelfoam(R)-matrices the release was diffusion controlled and it was affect ed by the pH of the external solution as well as the charge and molecular w eight of the studied compound. (C) 1998 Elsevier Science B,V. All rights re served.