ABSTRACT
Topical administration is direct, but conventional preparations of ophthalmic drugs, such as ointments, suspensions, or solutions, are relatively inefficient as therapeutic systems. Following administration, a large proportion of the topically applied drug is immediately diluted in the tear film and excess fluid spills over the lid margin and the remainder is rapidly drained into the nasolacrimal duct. A proportion of the drug is not available for immediate therapeutic action since it binds to the surrounding extraorbital tissues. In view of these losses, frequent topical administration is necessary to maintain adequate drug levels. Systemic administration of a drug to treat ocular disease would require a high concentrations of circulating drug in the plasma to achieve therapeutic quantities in the aqueous humor, with the increased risk of side effects.
