Which preservative is used as an alternative to BAK to reduce ocular surface toxicity?

• A. Purite
• B. Polyquad (polyquaternium-1)
• C. Sodium chloride
• D. Chlorobutanol

Answer: (B)

Preservatives in eye drops are chosen to balance antimicrobial protection with keeping the ocular surface healthy for daily use. Benzalkonium chloride (BAK) is effective but can be irritating and toxic to the corneal and conjunctival surface with chronic use.

Polyquad (polyquaternium-1) is a polymeric preservative that provides antimicrobial action while being gentler on the ocular surface. Its higher molecular weight means it doesn’t penetrate cells as readily as BAK, so it causes less disruption to the tear film, goblet cells, and epithelial cells. This translates to reduced toxicity and better tolerability for patients who need long-term therapy.

Other options like Purite degrade to water and oxygen after light exposure, which can lessen toxicity compared with BAK, but the question’s wording points to Polyquad as the alternative associated with lower ocular surface toxicity. Sodium chloride is not a preservative, and chlorobutanol is an older preservative with a higher potential for surface irritation.