Clinical Microbial Contamination of Multidose Brimonidine: A Prospective Comparison of Benzalkonium Chloride and...

To compare microbial contamination between multidose brimonidine eye drops preserved with benzalkonium chloride (BAK-MDB) and multidose brimonidine eye drops preserved with Purite® (PUR-MDB) using a comparative approach on the same patient under real-life conditions.

In this prospective study, 40 glaucoma patients used BAK-MDB and PUR-MDB for three weeks each. From each bottle, the cap and first and second drops were cultured on sheep blood and chocolate agar. Paired comparisons were performed using the exact McNemar test. Associations between patient-related factors and contamination were evaluated using Fisher's exact test and exploratory Firth-penalized logistic regression.

The contamination rates on the caps were similar between PUR-MDB and BAK-MDB on sheep blood agar (12.5% vs. 12.5%) and chocolate agar (10% vs. 12.5%) (exact McNemar test, all p > 0.05). The contamination rates of the first and second drops were lower than that of the cap, and no statistically significant difference was found between the drops (exact McNemar test, all p > 0.05). In univariate analysis, no difference was observed between contamination and patient-related factors (all p > 0.05). In exploratory multivariate analysis, a higher education level was independently associated with a significant reduction in contamination risk (OR: 0.09; 95% CI: 0.001-0.84; p = 0.031).

In our study, no statistically significant difference was observed between BAK-MDB and PUR-MDB in terms of microbial contamination in caps, first and second drops. The exploratory association between education level and contamination risk will need to be confirmed in larger, adequately powered prospective studies.