Effect of Low Concentrations of Benzalkonium Chloride on Acanthamoebal Survival and Its Potential Impact on Empirical Therapy of Infectious Keratitis

Abstract

The significant antiacanthamoebal effect of benzalkonium chloride, at or below concentrations used for preservation of common ophthalmic preparations, should be understood both when choosing empiric antibiotic therapy for infectious keratitis and when assessing the persistent rise in Acanthamoeba cases in the United States since 2003. Objective: To characterize the antiacanthamoebal efficacy of low concentrations of benzalkonium chloride (BAK) for drug preservation and therapeutic effect against Acanthamoeba. Design: Experimental study with a review of the literature. Setting: Laboratory. Exposures: A concentration of 10 4 trophozoites of 3 wellcharacterized clinical strains of Acanthamoeba were exposed at 0.5, 2.0, 3.5, 5.0, and 6.5 hours to BAK (0.001%, 0.002%, and 0.003%), moxifloxacin hydrochloride (0.5%), and moxifloxacin (0.5%)ϩBAK (0.001% and 0.003%) with hydrogen peroxide (3%) and amoeba saline controls. Main Outcomes and Measures: Amoeba survival was calculated using the most probable number method recorded as log kill values. The relationship of BAK concentration and exposure time as well as the relative effect of BAK and moxifloxacin on acanthamoebal survival were analyzed. Results: Amoebicidal activity of BAK is both time dependent and concentration dependent in pooled and strain-stratified analyses (P Ͻ.001). Moxifloxacin demonstrated no significant independent inhibitory effect or additive effect to BAK efficacy on acanthamoebal survival. The profound antiacanthamoebal effect of BAK, 0.003%, was similar to that of hydrogen peroxide for certain strains. Conclusions and Relevance: Low concentrations of BAK, previously demonstrated to concentrate and persist in ocular surface epithelium, exhibit significant antiacanthamoebal activity in vitro at or below concentrations found in commercially available ophthalmic anti-infectives. The unexplained persistence of the Acanthamoeba keratitis outbreak in the United States, clusters abroad, and clinical studies reporting resolution or modification of Acanthamoeba keratitis without specific antiacanthamoebal therapy suggests that other contributing factors should be considered, including changes in the formulations used for empirical therapy of presumed infectious keratitis occurring in the same period.

Can artificial tears prevent Acanthamoeba keratitis? An in vitro approach

“…In the case of the artificial tear Oculotect®, the preservative agent used is BAK, a known antibiotic and amoebicidal compound [ 20 ]. This study demonstrated that BAK, in its commercially available formulation, maintains good amoebicidal activity despite the other components of the artificial tear and even when the tear is diluted 1:1.…”

“…Hard contact lenses adsorb a small amount of this preservative and release a significant percentage of it during a regular washout procedure, approaching the upper safety limit, but soft contact lenses present a high adsorption of this substance. Such a property could allow the accumulation of BAK in the cornea epithelium, producing adverse effects [ 20 ]. Despite BAK’s toxicity, the promising results showed by Oculotect®, its use as a PrEP (pre-exposure prophylaxis) strategy before eye surgery should be considered.…”

“…Characteristics of the different tears are shown in Table 1 . Benzalkonium chloride (BAK) which interrupts the lipid component of cell membranes acting as an antibiotic and amoebicidal) is a detergent found in Oculotect® (Laboratoires Alcon, Kaysersberg, France) [ 20 ]. Purite® (Allergan, Westport, Ireland) is a stabilized oxychloride complex with chlorine dioxide, chlorite and chlorate found in Optava Fusion™ (Allergan, Westport, Ireland).…”

“…Non-effect control was performed with NEFF saline. These cultures were incubated at 33 °C for 2 h, 4 h, 6 h and 8 h as previously described [ 20 – 22 ]. Before culture collection, the appearance of the Acanthamoeba trophozoites was checked under light microscopy at 400× (Nikon Eclipse TS100, Nikon Instruments Europe B.V.).…”

In Vitro Evaluation of the Inhibitory Effect of Topical Ophthalmic Agents on Acanthamoeba Viability

“…Furthermore, empirical antibiotic treatment with fluoroquinolone drugs or other biocides prior to diagnosis could have an effect on the viability of Acanthamoeba . Aside from the antimicrobial drugs, many ophthalmic preparations utilize benzalkonium chloride (BAC) as a preservative, and it has been shown that BAC is highly toxic to Acanthamoeba 19…”