| Popis: |
Summary Interaction studies by Boston lens material, both as powder and lenses with benzalkonium chloride (BAK) in simple aqueous solution and a model isotonic phosphate buffer system, pH 7.0, have been carried out and the results compared with data for PMMA. The level of interaction with Boston material increased with temperature and the presence of electrolyte. Over the concentration range of clinical interest (0.002 – 0.01% BAK) the uptake by both Boston lenses and powder on a polymer weight basis was not significantly greater (and often less) than that for the PMMA under the corresponding conditions. The nature of the Boston-BAK interaction is clearly different in character from that of the PMMA-BAK interaction; the latter produces typical L type isotherms whereas with Boston material sigmoidal type hysteresis isotherms are obtained. As evidenced by the powder-buffer data at 30°, the desorption of BAK from Boston material is only partially reversible and alternative mechanisms involving two or three types of binding site are proposed to account for this behaviour. Uptake studies by Boston lenses equilibrated in twocommercial products, Kelsoak and Kelvinol, resulted in low levels of interaction which were not significantly different to those of PMMA lenses with these products. Interaction with these formulated products were less than predicted from the interactions found in the model isotonic buffer formulation. After three months storage in the commercial formulation vehicles containing up to 0.2% benzalkonium chloride, there were no changes in the physical and optical characters of the lenses. |
