Drug delivery to the posterior eye segment is an important challenge in ophthalmology,
because many diseases affect the retina and choroid leading to impaired vision or
blindness. Currently, intravitreal injections are the method of choice to administer
drugs to the retina, but this approach is applicable only in selected cases (e.g.
anti-VEGF antibodies and soluble receptors). There are two basic approaches that can
be adopted to improve retinal drug delivery: prolonged and/or retina targeted delivery
of intravitreal drugs and use of other routes of drug administration, such as periocular,
suprachoroidal, sub-retinal, systemic, or topical. Properties of the administration
route, drug and delivery system determine the efficacy and safety of these approaches.
Pharmacokinetic and pharmacodynamic factors determine the required dosing rates and
doses that are needed for drug action. In addition, tolerability factors limit the
use of many materials in ocular drug delivery. This review article provides a critical
discussion of retinal drug delivery, particularly from the pharmacokinetic point of
view. This article does not include an extensive review of drug delivery technologies,
because they have already been reviewed several times recently. Instead, we aim to
provide a systematic and quantitative view on the pharmacokinetic factors in drug
delivery to the posterior eye segment. This review is based on the literature and
unpublished data from the authors' laboratory.