Purpose: To study the aqueous and vitreous penetration of ciprofloxacin after prolonged acute topical administration and to investigate the effects of inflammation on drug penetration. Methods: A standardized model of intraocular infection after penetrating injury was made in the right eyes of eight rabbits. The intact left eyes were maintained as the control. Two drops of ciprofloxacin 0.3% eyedrops were instilled topically every 1 h for 7 h to all eyes of the rabbits. Aqueous and vitreous samples (100 mu l) were obtained half an hour after the last drop. Instillation was continued for 7 h more and samples were obtained as before. Drug concentrations were measured using HPLC. Results: The mean aqueous humor levels of ciprofloxacin were: in control eyes 1.31 +/- 0.78 mu g/ml after 7 h and 1.85 +/- 1.69 mu g/ml after 14 h of instillation; in inflamed eyes 2.18 +/- 1.02 mu g/ml after 7 h and 2.91 +/- 2.12 mu g/ml after 14 h. The mean vitreous humor levels were: in control eyes 0.65 +/- 0.44 mu g/ml after 7 h and 0.72 +/- 0.8 mu g/ml after 14 h of instillation; in inflamed eyes 0.67 +/- 0.77 mu g/ml after 7 h and 1.01 +/- 0.43 mu g/ml after 14 h. However, the differences among the groups were not significant (P > 0.05). Conclusions: Ciprofloxacin penetration into aqueous humor was higher in 14-h topical application than that for 7 h. Inflammation increased the penetration of topical ciprofloxacin into aqueous while administered for 7 h and into both aqueous and vitreous humor while administered for 14 h. (C) 2000 Elsevier Science B.V. All rights reserved.