Comparison of two hydrogel formulations for drug release in ophthalmic lenses

In the present work two types of polymers were investigated as drug releasing contact lens materials: a poly-hydroxyethylmethacrylate (pHEMA) based hydrogel and a silicone hydrogel. The silicone hydrogel resulted from the addition of TRIS, a hydrophobic monomer containing silicon (3-tris(trimethylsilyloxy)silylpropyl 2-methylprop-2-enoate), to pHEMA. Both hydrogels were loaded with an antibiotic (levofloxacin) and an antiseptic (chlorhexidine) by soaking in the drug solutions. The hydrogel properties were determined to be within the range demanded for lens materials. The release profiles of both drugs from the hydrogels were obtained and eventual drug/polymer interactions were assessed with the help of Raman spectra. A mathematical model, developed to mimic the eye conditions, was applied to the experimental results in order to predict the in vivo efficacy of the studied systems. The release profiles were compared with those resulting from the application of commercial eyedrops. The pHEMA based hydrogel demonstrated to be the best material to achieve a controlled release of levofloxacin. In the case of chlorhexidine, the silicone hydrogel seems to lead to better results. In both cases, our results suggest that these materials are adequate for the preparation of daily disposable therapeutic contact lenses.