1096 SECTION XIV Ophthalmology Table 63-1
Some Characteristics of Ocular Routes of Drug Administration*
Limitations and Precautions
Subconjunctival, sub-Tenon's, and retrobulbar injections
Intraocular (intracameral) injections Intravitreal injection or device
Prompt, depending on formulation
Prompt or sustained, depending on formulation
Absorption circumvented, immediate local effect, potential sustained effect
Convenient, economical, relatively safe
Anterior segment infections, posterior uveitis, cystoid macular edema
Anterior segment surgery, infections
Compliance, corneal and conjunctival toxicity, nasal mucosal toxicity, systemic side effects from nasolacrimal absorption Local toxicity, tissue injury, globe perforation, optic nerve trauma, central retinal artery and/or vein occlusion, direct retinal drug toxicity with inadvertent globe perforation, ocular muscle trauma, prolonged drug effect Corneal toxicity, intraocular toxicity, relatively short duration of action Retinal toxicity
*See text for more complete discussion of individual routes.
Drug penetration into the eye is approximately linearly related to its concentration in the tear film. Certain disease states, such as corneal ulcers and other corneal epithelial defects, may increase drug penetration when anatomic barriers are compromised or removed. Experimentally, drugs may be screened for their potential clinical utility by assessing their corneal permeability coefficients. These pharmacokinetic data combined with the drug's octanol/water partition coefficient (for lipophilic drugs) or distribution coefficient (for ionizable drugs) yield a parabolic
figure 63-2 Anatomy of the lacrimal system.
Interior lacrimal papilla and puncta figure 63-2 Anatomy of the lacrimal system.
relationship that is a useful parameter for predicting ocular absorption. Of course, other factors also affect corneal absorption in vivo, such as epithelial integrity, blink rate, dilution by tear flow, nasolacrimal drainage, drug binding to proteins and tissue, and transconjunctival absorption.
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