The use of ophthalmic lenses as drug carriers seems a promising option for the sustained delivery of ocular drugs. Ophthalmic lenses sterilization is mandatory to fulfil strict microbiological safety requirements. However, it must not compromise the drugs or material properties and must allow keeping adequate drug release profiles.
The goal of this study was to investigate the effect of two sterilization methods, steam heat (SH - 60 min, 121oC and 1 bar) and γ-irradiation (doses: 5, 15 and 25 kGy) on two polymeric materials used to produce ophthalmic lenses (a contact lens and an intraocular lens material) loaded with two ophthalmic drugs (diclofenac and moxifloxacin).
The impact of the sterilization procedures on the stability and antimicrobial activity of the drugs as well as on the properties of lenses materials was assessed. The activity of the drugs was studied by high performance liquid chromatography (HPLC) and microbiological tests were performed against two strains of bacteria (Staphylococcus aureus and Staphylococcus epidermidis) for moxifloxacin. The materials were characterized relatively to transmittance (UV-Vis spectroscopy), swelling behaviour and wettability (captive bubble method). Drug release experiments were carried out at 36ºC in sink conditions, before and after sterilization.
Results of both HPLC and microbiological assays showed that SH sterilization did not induce drug degradation, while γ-irradiation led to different results: 5 kGy did not lead to significant changes on drug activity but 15 and 25 kGy led to degradation. For this reason, the higher radiation doses were abandoned in the following studies. Concerning the materials properties, SH and γ-irradiation at 5 kGy did not affect the studied properties. The drug release experiments showed that SH sterilization improved significantly the release profiles of the intraocular lens material loaded with both studied drugs.