Intraocular irritation evaluation of benzalkonium chloride in rabbits

The purpose of this study was to define the threshold for intraocular irritation of benzalkonium chloride, a preservative used in some formulations which enter the anterior segment of the eye during ocular surgery. Various concentrations of benzalkonium were injected into anterior chambers of albino rabbit eyes. Conjunctivitis, flare, iritis, and corneal changes occurred in a dose response pattern. The threshold of irritation was 0.03%, with highest nonirritating concentration being 0.01%. In other works in this laboratory, threshold of irritation for topical ocular benzalkonium was 0.05%, but the nature of ocular changes was less substantial than those observed intraocularly. Because the threshold for intraocular irritation is less than that topically, the nature of ocular changes was different for two routes, and there is a paucity of clinical data for intraocular benzalkonium chloride, a safety factor of 10 was utilized in setting the highest safe concentration of 0.001% for intraocular use. The preservative efficacy of 0.001% is questionable; therefore, we cannot endorse benzalkonium chloride as a preservative for formulations which will enter the anterior segment of the eye.