Purpose: To determine the antibacterial activity of the white crystalline precipitate formed on the corneal surface after topical administration of 0.3% ciprofloxacin ophthalmic solution by microbiologic assay.
Methods: White crystalline precipitate formed on the corneal surface of seven patients was scraped and individually dissolved in sterile distilled water. Quantification by high-performance liquid chromatography (HPLC) and microbiologic assay of ciprofloxacin in the precipitate solutions were done. Microbiologic assay was performed by agar diffusion method against Klebsiella pneumoniae.
Results: By HPLC, concentrations of ciprofloxacin were estimated to be 1.5-60 microg/ml in the dissolved precipitate obtained from six patients, whereas the concentrations based on microbiologic assay varied from 1.6 to 16.1 microg/ml. Ciprofloxacin was not detected by either method in the precipitate obtained from one patient. The antibacterial activity (microg/ml) determined by microbiologic assay was not related to the actual amount of ciprofloxacin in the solutions as estimated by HPLC in cases 1, 2, 4, and 7. It was almost the same in the solutions from cases 5 and 6.
Conclusion: The white crystalline precipitate formed on the corneal surface after topical administration of 0.3% ciprofloxacin ophthalmic solution exhibited bacterial inhibitory activity, indicating that the precipitate may function as a drug depot.