Age-related differences in ophthalmic drug disposition II: drug-protein interactions of pilocarpine and chloramphenicol.

Although drug-protein interactions have been shown to be important in the transport of drugs into and through the eye, age-related differences in ocular drug-protein binding have not been explored. This study was designed to investigate protein binding characteristics of pilocarpine and chloramphenicol in aqueous humour and plasma from rabbits of different ages. The method of equilibrium dialysis was used to quantitate drug-protein interactions. Younger animals showed decreased binding of chloramphenicol in plasma when compared to older rabbits. On the other hand, the interactions of both drugs with aqueous humour proteins were more extensive in younger rabbits. Age-related differences in drug-protein binding were not directly related to the total protein contents of the respective biological fluids. These findings suggest possible age-related differences in the relative protein fractions contained in aqueous humour and plasma, or qualitative differences in the binding capacity of the proteins involved.