Chlorhexidine kinetics of hydrophilic contact lenses

Abstract

An average chlorhexidine concentration of 4·5 μg mg−1 lens (wet weight) was measured in HEMA‐based contact lenses after 16 days of the following treatment. The lenses were maintained 16 h daily in 1·5 ml of a solution containing Chlorhexidine digluconate 0·005%, and then worn by adult albino rabbits 8 h daily. Similarly maintained, but unworn lenses contained approximately 23 μg Chlorhexidine mg−1 wet lens weight after 16 days. A plot of the results indicates that continued exposure to Chlorhexidine following initial immersion increased its concentration in unworn lenses while that in the worn lenses reached a peak at 8 days, then decreased slightly in the subsequent days of wearing. Continuous exposure of lenses to the disinfecting solution (1 lens/167 ml) in which the Chlorhexidine concentration was maintained at 0005% for 16 days gave a maximal concentration of 44 μg mg−1 wet lens weight. The comparatively small concentration in a worn lens results from: (1) daily loss from the lens during wear, a large percentage of which is apparently absorbed to tear proteins which subsequently flow from the eyes via the canaliculi; (2) limited uptake because of the small immersion volume employed in routine storage; and (3) the possible competition between Chlorhexidine and tear components for lens binding sites or establishment of an equilibrium condition between uptake and release.

The Role of Polymer Permeability in the Control of Drug Release

“…The linear relationship between M, and t that occurs when the steady state is reached in the release of drug from a device with slab geometry is given by eqn (5) (5) where em is the uniform concentration of drug that exists initially in the membrane. In addition, the diffusion coefficient of the drug in the membrane can be derived from eqn (6), (6) where tB is the negative intercept on the time axis in the plot shown in Fig. 5.…”

Response to the Report ‘Influence of Soft Contact Lens Solutions on Rabbit Cornea’ by Dreifus and Wobmann

“…For example, the use of corneal epithelial tissue cultures is an excellent method which provides the investigator with a system for the study of the effects of chemicals in a population of the cells concerned. However, even with such a system one does not duplicate either the corneal epithelium or the surface milieu resulting from the regular influx and efflux of tears, the associated dilution of any instilled solutions [3] and the protein binding of chemicals to the soluble tear proteins [4], The use of experimental animals provides a host of other problems. These include the general lack of enthusiasm exhibited for lens wearing, as well as anatomical and physiological differences.…”