Thus far, the influence of age on the bioavailability of topically applied ophthalmic drugs has been studied by considering age-dependent changes in membrane permeability and protein binding. The specific objective of this research was to determine variation of ocular esterase activity with age and pigmentation of the rabbit. This was achieved by monitoring the fluorescence intensity as a function of time upon incubating ocular tissue homogenates of albino and pigmented rabbits of various age groups with α-naphthyl acetate, both in the presence and absence of esterase inhibitors. In general, esterase activity was the highest in the iris-ciliary body followed by the cornea and then the aqueous humor. Of the age groups studied, peak ocular esterase activity was reached at 6 weeks in the albino rabbit, and beyond 6 weeks in the pigmented rabbit. In the 6-week-old group the albino rabbit exceeded the pigmented rabbit in ocular esterase activity, whereas in the 12-week-old group it was the pigmented rabbit that exceeded the albino rabbit in ocular esterase activity. The conclusion was that in establishing a dosage regimen, age-dependent changes in ocular esterase activity must be considered in conjunction with age-dependent changes in the other factors that also help determine the amount of active drug ultimately reaching its receptor.
ASJC Scopus subject areas
- Pharmaceutical Science