Adsorption of actives in ophthalmological drugs for over-the-counter on soft contact lens surfaces.

The adsorption of various kinds of ionic/nonionic actives, added in ophthalmological drugs (artificial tear, contact lens wetting solution, eye-drops, and eyewash) for over-the-counter (marketable drugs with no need of any medical prescription) , on soft contact lens (SCL) surfaces has been studied as a function of hydrophobicity of the actives. The common logarithm of the 1-octanol/water partitioning coefficient (AC_log P) has been used in order to normalize the hydrophobicity of the actives employed in this study. No significant adsorption occurs for relatively hydrophilic actives, whereas the adsorption rate is gradually increased with an increase in the hydrophobicity of the actives. This suggests that the adsorption is predominantly governed by the hydrophobic interaction of the actives with the SCL surfaces, although an electrostatic interaction plays an additional role for the adsorption. The most effective adsorption occurs in the following active-lens combinations: cationic actives--the anionic and hydrated lens IV (methacrylic acid-based SCL); anionic actives---the nonionic and hydrated lens II (N-vinyl pyrrolidone-based SCL); and nonionic actives--the anionic and less-hydrated lens III (containing hydrophobic silicone monomers).