The effect of chronic administration of a topical antibiotic on the conjunctival flora

Twenty-two volunteers received topical 0.25% chloromycetin ophthalmic drops without preservatives and 20 received topical 1% methylcellulose ophthalmic drops in their right eyes for up to 12 weeks. The left eyes served as controls. The eye drops were used an average of 3.21 times per day. A slit lamp biomicroscope examination, conjunctival cultures, and antibiotic sensitivities were performed on each visit. No difference in the percentage of positive cultures or negative cultures obtained in the chloromycetin treated eyes could be found when compared with the methycellulose treated group or control eyes. Chloromycetin 0.25% ophthalmic drops without preservative appear to be questionably effective, although harmless, when used for up to 12 weeks, 3 to 4 times per day.