Benzalkonium chloride

How it works

As a cationic surfactant it disrupts microbial cell membranes, preventing contamination of the product; it also disrupts the corneal epithelial barrier, which can enhance penetration of co-formulated drugs.

Prescribing in practice

• Long-term or frequent exposure can cause ocular surface toxicity and dry eye, so prefer preservative-free preparations in patients on multiple or long-term eye drops.
• It can be absorbed by and discolour soft contact lenses, so lenses should be removed before instillation.
• Patients with pre-existing ocular surface disease are particularly susceptible to its irritant effects.

Monitoring

Monitor for signs of ocular surface toxicity such as stinging, redness and worsening dry eye in patients on preserved drops long term.

Counselling the patient

• If your eyes become persistently irritated on long-term drops, ask whether a preservative-free option is suitable.
• Remove soft contact lenses before using drops containing this preservative and wait before reinserting.
• Report persistent burning, redness or grittiness.

Evidence & guidelines

Benzalkonium chloride is the most common ophthalmic preservative, and its ocular surface toxicity with long-term use is well recognised in the ophthalmic literature.