Objective: To compare the efficacy of two treatment regimens, tobramycin drops-erythromycin ointment and ofloxacin drops-placebo ointment, in sterilizing the external ocular adnexa when given perioperatively. A second objective was to determine the aqueous humour concentration of ofloxacin and tobramycin.
Design: Randomized double-blinded clinical trial.
Setting: University-affiliated hospital.
Patients: Patients aged 18 years or more scheduled to undergo planned cataract surgery who were judged likely to complete the trial.
Numbers: Of 55 patients enrolled 6 were disqualified and 49 completed the trial.
Interventions: Preoperative instillation of 10 drops of a 0.3% solution of ofloxacin (26 eyes) or tobramycin (23 eyes) in the operative eye, starting the evening before surgery. Tobramycin-treated eyes received erythromycin ointment after surgery; ofloxacin-treated eyes received petrolatum ointment. Lid and conjunctival swabs were obtained from both eyes on the day before surgery (visit 1), at surgery (visit 2) and on the first postoperative day (visit 3). Aqueous humour samples were obtained from the study eyes at surgery.
Main outcome measures: Threshold growth of bacteria on culture, aqueous humour concentration of ofloxacin or tobramycin.
Results: At visit 1, 96% of all eyes had positive cultures; this result persisted at visits 2 and 3 for the control eyes. For the treated eyes the incidence of positive cultures decreased from visit to visit. By visit 3 lid cultures were positive for 7 (27%) of the ofloxacin-treated eyes and 7 (30%) of the tobramycin-treated eyes; conjunctival cultures were positive for 0 (0%) of the ofloxacin-treated eyes and 1 (4%) of the tobramycin-treated eyes. No significant differences were seen in culture positivity between the treatment groups at any visit. The mean aqueous humour concentration of ofloxacin was significantly higher than that of tobramycin (0.4084 vs. 0.0279 microgram/mL) (p < 0.001).
Conclusions: Both ofloxacin-placebo treatment and tobramycin-erythromycin treatment were more effective than no treatment in sterilizing the external ocular adnexa. The two treatments were equally efficacious in eliminating bacteria, more successfully in the conjunctiva than the lids. Topically administered ofloxacin demonstrated significantly greater anterior chamber penetration than topically administered tobramycin.