Eye Catching Study: The Truth About Benzalkonium Chloride
Study suggests benzalkonium chloride, a preservative that has been used in ophthalmology since the 1940s, may be toxic to ocular structures.
Benzalkonium chloride (BAK) is a preservative that has been used in ophthalmology since the 1940s, and is found in up to 70% of eye drops. BAK, a quaternary ammonium compound, acts as a detergent, lysing cell membranes, and killing microorganisms. This makes it very effective as a preservative.
Preservatives are used in ophthalmic medications because they are cost effective. A large bottle of eye drops can last an entire month when a preservative is added compared with preservative free (PF) counterparts.
Now, a review published in the British Journal of Ophthalmology suspects that BAK might be toxic to ocular structures. The supporting science is based on laboratory and animal studies demonstrating its toxicity. In one study, BAK stimulated an apoptotic response to corneal cells. At a molecular level, dose-dependent DNA damage has been associated with BAK.
The researchers searched for studies comparing preservative and PF drops. One variable researchers examined was ocular surface disease (OSD) which they define as “an umbrella term that includes dry eye, lid disease, conjunctivitis, and keratitis.” Many studies use different subjective measures when evaluating the severity of OSD.
A survey found that those on PF drops had roughly half the signs and symptoms of OSD compared to those on preserved drops. However, this should be taken with a grain of salt because several other clinical studies found little to no corneal toxicity from various concentrations of BAK.
One study limitation was the lack of masked randomized controlled trials (RCTs) that compare PF drops directly with the same drop containing preservative. That said, some studies have compared non-BAK preserved and BAK preserved eye drops. In these comparisons, BAK was no more toxic than other preservatives.
Pharmacists and other healthcare providers should recommend PF drops in patients with established OSD. In these patients, switching to PF medications has been shown to improve symptoms, signs and tolerability. Patients on multiple medications (3 or more) may also benefit from a PF preparation. Other factors to consider when selecting the right eye drop are cost, patient preference, tolerability, frequency, and duration of use.
Mohammad Waleed is a 2019 PharmD Candidate at the University of Connecticut.
Steven DW, Alaghband P, Lim KS. Br J Ophthalmol Epub ahead of print: 2018 May 12. doi:10.1136/ bjophthalmol-2017-311544