Physico-chemical, in vitro and in vivo characterisation of polymers for ocular use

The influence of artificial tear fluid (AT) on ionic and nonionic ophthalmic polymer excipients was rheologically established. In usual concentrations polyvinylalcohol, polyvinylpyrrolidone, dextran, hydroxypropylmethylcellulose, hydroxyethylcellulose and methylcellulose did not show any changes. In contrast, solutions of polyacrylic acid, sodium hyaluronate (S-Hya), sodium alginate (S-Alg) and chitosan decrease the apparent viscosity in contact with AT, while gellan solution increases the viscosity and shows thixotropy. The adhesion of selected polymers (polysaccharides) on mucin was evaluated using a rheological method and resulted in the order S-Hya > Gellan > S-Alg > dextran. Miosis testing of Gellan containing pilocarpine HCl formulations in rabbits shows a possible reduction of drug concentration from 2% to 0.5% obtaining the same bioavailability.