The effect of trimethoprim-polymyxin B sulphate ophthalmic ointment and chloramphenicol ophthalmic ointment on the bacterial flora of the eye when administered to the operated and unoperated eyes of patients undergoing cataract surgery.

Both eyes of patients undergoing cataract surgery were treated with an ointment preparation containing either trimethoprim 5 mg/g and polymyxin B sulphate 10,000 units/g, or chloramphenicol 1%. The antibiotic preparations were administered four times daily on the day prior to surgery, once in the morning prior to surgery and twice daily for fourteen days post-operatively. Cultures from conjunctivae and lid margins were taken prior to treatment, pre-operatively and post-operatively on selected days including the fourteenth post-operative day. The effect of the antibiotics on conjunctival and lid margin flora was determined by enumerating patients with positive cultures prior to treatment which were eradicated following treatment and patients with organisms which were cultured de novo in spite of antibiotic treatment. There was no significant change in the number of patients with organisms isolated from conjunctivae and lid margins (p greater than 0.1 in each case, Sign test) over the sixteen day study period with either treatment. Additionally, when the effect of the two preparations on the number of patients with organisms obtained from conjunctivae and lid margins was compared, there was no significant difference between them (p greater than 0.1 conjunctival cultures, p greater than 0.1 lid margin cultures, Fisher's Exact probability test).