Purpose: Adenoviral conjunctivitis is the most common cause of conjunctivitis worldwide with no approved antiviral treatment. Benzalkonium chloride (BAK) is a common preservative in ophthalmic medications and is the active ingredient in some skin disinfectants and hand sanitizers. BAK is known to be effective in killing bacteria and enveloped viruses; however, its activity against ocular types of nonenveloped adenoviruses (Ads) is unknown. The goal was to determine whether BAK is an effective antiviral agent against common human ocular types of adenovirus in vitro. Methods: The direct inactivating activity of BAK was determined by incubating several human adenovirus types with BAK concentrations of 0.001%, 0.003%, 0.005%, 0.01%, 0.1%, and 0% for 1 h at 33°C. Resulting adenovirus titers were determined after treatment. Decreases in titers of ≥3 Log₁₀ were considered virucidal, while decreases in titers of <1 Log₁₀ were considered ineffective. Results: BAK 0.1% was virucidal for Ad3, Ad5, Ad7a, Ad19/64, and Ad37, while it reduced titers >1 Log₁₀, but <3 Log₁₀ for Ad4 and Ad8. Decreases in titers >1 Log₁₀ were demonstrated for BAK 0.003%, 0.005%, and 0.01% for Ad5 only. Decreases in titers for the other adenovirus types for those concentrations were ≤0.53 Log₁₀. 0.001% BAK produced minimal decreases in titers for all types. Conclusions: BAK, at 0.01% or less was not consistently effective as an antiviral against adenovirus, but higher concentrations, such as 0.1%, should be further investigated as a possible topical treatment for adenoviral ocular infections, providing ocular toxicity is not an issue.

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