Preservatives in Topical Ophthalmic Medications: Historical and Clinical Perspectives

P. David Freeman; Malik Y. Kahook


Expert Rev Ophthalmol. 2009;4(1):59-64. 

In This Article

Oxidizing Preservatives

Oxidative preservatives alter the lipid membrane of microbes in a different fashion to detergent preservatives, by penetrating the membrane and altering the DNA, protein and lipid components of bacterial cells.[4] Oxidizing preservatives are considered second-generation ophthalmic preservatives and were developed because of their reduced toxicity to human ocular surface cells in comparison with detergent preservatives. Although ocular surface cells may still be injured by oxidative preservatives, the low concentrations contained in ophthalmic preparations deem these effects insignificant.[4] Noecker et al. reported that medications preserved with Purite® induce less corneal toxicity than those preserved with BAK.[5] Examples of oxidizing preservatives include sodium perborate and stabilized oxychloro complex (SOC).

Recently Introduced Ionic-buffered Preservatives

Ionic-buffering systems are the latest class of ophthalmic preservatives to be incorporated into topical medicines and act in a similar manner to oxidizing preservatives within multidose bottles. SofZia (Alcon, TX, USA), the most recent preservative of this kind, is a combination of boric acid, zinc, sorbitol and propylene glycol. This ionic-buffered system has been shown to have both antibacterial and antifungal qualities.[6] When exposed to cations, such as those that are normally encountered in the tear film of the eye, the substance is deemed inactive. This is thought to induce less cytotoxicity to the ocular surface compared with more conventional preservatives.