Why the preservative in a bottle of eye drops matters more the longer a patient stays on it.
Every multi-dose eye drop needs some way of staying sterile once opened. How that is achieved matters, particularly for patients on therapy for months rather than days.
Benzalkonium chloride (BKC)
BKC is the most widely used ophthalmic preservative. It is effective and inexpensive. It is also a detergent: with frequent, long-term exposure it can disrupt the tear film lipid layer and irritate the ocular surface — which is unhelpful in exactly the patients, such as those with dry eye or glaucoma, who use drops most.
Stabilized oxychloro complex
This preservative breaks down on exposure to light and the ocular surface into components already present in tears — chloride ions, oxygen and water. It preserves the bottle but carries a lighter surface burden. Products in our range marked BKC FREE, such as Blugat, Mogem-LP and Nefanex Plus, use this system.
Self-preserving formulations
Some formulations are stable enough to need no added preservative. Blutob-Max and Mogem-D are marked Preservative Free on the carton for this reason.
What this means in practice
For a short antibiotic course, a BKC-preserved drop is usually unremarkable. For chronic lubricant use, long steroid tapers or glaucoma therapy, a lower preservative burden is worth asking about. Once opened, any multi-dose vial should still be used within one month.