Effect of norfloxacin and clonidine on human trabecular meshwork cells in vitro.

We evaluated the effect of norfloxacin and clonidine on the morphology, DNA synthesis and phagocytic activity of cultured human trabecular meshwork cells in the 3rd-5th generations. Exposure to norfloxacin at a concentration of 1.5 x 10(-4) g ml-1 for 6 h led to retraction of cytoplasmic processes and rounding of cell profile, and exposure for 48 h caused cell death. Exposure to clonidine at 1.0 x 10(-3) g ml-1 for 12 h caused cell degeneration, and exposure for 72 h led to cell death. The morphologic changes were dose-time dependent. Tritiated thymidine incorporation was determined as an index of DNA synthesis, which was significantly inhibited by 1.5 x 10(-5) g ml-1 norfloxacin or 1.0 x 10(-3) g ml-1 clonidine, but obviously enhanced by 1.0 x 10(-4) and 1.0 x 10(-5) g ml-1 clonidine. Both drugs inhibited phagocytosis of latex microspheres in a dose-dependent mode. According to the presented results and the pharmacokinetic data reported in the literature, we suggest that the topical use of norfloxacin should not be too frequent or continued too long, especially when the corneal epithelium was not intact; clonidine has no deleterious effect on trabecular cells in its conventional use.