Contact lens(CL) solutions with H2O2 or povidone-iodine (P-I) are “the only solution categories effective against Acanthamoeba,” according to a review published in Clinical Optometry. They are, therefore, “preferred for any patient who may expose their CLs to water.” 

Although Acanthamoeba infections are rare, when they do occur they can quickly become sight-threatening, the study says. Neither of the modern, high-molecular-weight preservatives polyquaternium-1 (PQ-1) or biguanides (PHMB) are effective against the microbe, although they do have an effective response against bacteria, and a minimally-effective response against fungi, researchers explain. Presently, PHMB-based multipurpose solutions (MPS) comprise 60% of the US market, and most of China’s market, according to the review.

The researchers assessed PubMed records of 4 types of ophthalmic preservatives, and compared nonpreserved contact lens solutions with preserved MPS. The mechanism of action of P-I, which is not yet available in contact lens solutions in the US, involves penetration of microbial cell walls and attack of proteins and DNA, causing apoptosis. One of the studies reviewed analyzed P-I solutions’ antimicrobial activity and potential cytotoxicity, compared with P-I to H2O2, PHMB MPS, and a benzalkonium chloride (BAK)  solution and found P-I “both the most effective disinfectant against the tested bacteria and fungus and the least cytotoxic of the 4 solutions, making it a promising recent innovation in the CL disinfection market,” the study says. However, additional research suggests H2O2 is the most effective of the 4 solution types at the shortest storage times against Acanthamoeba


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Although innovative strides are being made, the study’s authors report that the market lacks a perfect care system for contact lenses. They also stress that MPS studies “may vary depending on study design, study duration, and additional components in the solution (other than the preservatives), so outcomes should be monitored clinically. While various studies have assessed multiple MPS with different preservatives, or MPS containing more than one preservative, many have yielded conflicting results, and none make definitive recommendations for the use of 1 preservative over another.”

Disclosure: Some study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.

Reference

Bradley CS, Sicks LA, Pucker AD. Common ophthalmic preservatives in soft contact lens care products: benefits, complications, and a comparison to non-preserved solutions. Clin Optom. Published online September 7, 2021. doi:10.2147/OPTO.S235679