Clearance of sodium fluorescein incorporated into microspheres from the vitreous after intravitreal injection

The clearance of microsphere-bound fluorescein from the vitreous was studied in rabbits to evaluate microspheres as a controlled-release drug delivery system. Microspheres of different combinations of copolymers of lactic and glycolic acid were injected intravitreally in three groups of rabbits. High concentrations were detected in the vitreous of all groups within 24 hours. By 5 days, the levels had gradually decreased, but they remained measurable up to 16 days in the rabbits in which lactide microspheres had been injected. Clearance was more rapid in the lactide/glycolide combination group than in the lactide group.