Chlorhexidine loss from simulated contact lens solutions stored in glass and plastic packages.

A storage test on chlorhexidine gluconate (0.004%) in aqueous or simulated contact lens solutions, conducted for 6 months in various containers, suggested [l] that loss of activity by a surface adsorption process was occurring. It has been reported [2] that contact lens solutions containing chlorhexidine gluconate (0.~5%) stored at room temperature in the dark for 6 months in polypropylene, polyethylene, and amber and clear glass, showed an antiseptic loss of 4-10% in plastic containers and, unexpectedly, of 16% and 25% in amber and clear glass respectively. However, the type of glass employed was not stated. More recently [3], storage experiments on ophthalmic drops containing benzalkonium chloride or chlorhexidine acetate indicated no adsorption by glass or ~lyethylene containers. The calorimetric method [4] used in this case for assaying the preservatives has been criticized as yielding large errors [5] and as unsuitable for the determination of chlorhexidine salts [6]. Chlorhexidine gluconate (O.OOl-0.006%), combined with benzalkonium chloride or thiomersal, is widely employed as a preservative in contact lens solutions. These solutions are ~mmonly packaged in polyolefin containers and many regulatory authorities demand that there should be no container-preservative interaction. Recently the present workers described [6] a rapid and reliable calorimetric method for determining chlorhexidine gluconate in commercial contact lens solutions through the formation of a stable ion-pair with methyl orange. The ion pair can be extracted with chloroform without interference from other ingredients or from 4-chloroaniline, the main breakdown product of chlorhexidine. The present paper reports the application of