Effect of oily vehicle on ocular pilocarpine concentration

Non-aqueous formulations in topical ocular drug delivery - a paradigm shift?

Topical eyedrop application is the preferred route for drug delivery to anterior segment tissues; however, the challenge of overcoming the eye's anatomical and physiological barriers while minimising tissue toxicity has restricted developments in this field. Aqueous vehicles have traditionally been used, which typically require several additives and preservatives to achieve physiologically compatible and sterile eyedrops, elevating their toxicity potential. Non-aqueous vehicles have been suggested as efficient alternatives for topical drug delivery as they can address many of the limitations associated with conventional aqueous eyedrops. However, despite their obvious advantages, non-aqueous eyedrops remain poorly researched and few non-aqueous formulations are currently available in the market. This review challenges the conventional hypothesis that aqueous solubility is a prerequisite to ocular drug absorption and establishes a rationale for using non-aqueous vehicles for ocular drug delivery. Recent advances in the field have been detailed and future research prospects have been explored, pointing towards a paradigm shift in eyedrop formulation in the near future.

Topical ocular drug delivery: recent developments and future challenges

Existing ocular drug delivery systems are fairly primitive and inefficient, but the stage is set for the rational design of newer and significantly improved systems. The focus of this review is on recent developments in topical ocular drug delivery systems relative to their success in overcoming the constraints imposed by the eye and to the improvements that have yet to be made. In addition, this review attempts to place in perspective the importance of pharmacokinetic modeling, ocular drug pharmacokinetic and bioavailability studies, and choice of animal models in the design and evaluation of these delivery systems. Five future challenges are perceived to confront the field. These are: (a) The extent to which the protective mechanisms of the eye can be safely altered to facilitate drug absorption, (b) Delivery of drugs to the posterior portion of the eye from topical dosing, (c) Topical delivery of macromolecular drugs including those derived from biotechnology, (d) Improved technology which will permit non-invasive monitoring of ocular drug movement, and (e) Predictive animal models in all phases of ocular drug evaluation.

Corneal penetration and ocular bioavailability of drugs

This article reviews the objectives which must be considered in producing optimal formulations for topical ophthalmic use. The effects of preservatives, vehicles, and adjunct agents are described. Anatomical considerations which impact bioavailability of the drug at the desired target site are discussed in detail. Model systems that can aid in determining the best formulations for preclinical and clinical testing are also reviewed. The long term objective of this review is the development of formulations for optimal efficacy and safety, considering all the requirements of the patient.

Pharmacokinetics of topically applied ophthalmic drugs

Pharmacokinetic applications in recent years have led to significant advances in systemic drug therapy, but applications to topical, ophthalmic therapy have been far less numerous. Pharmacokinetics is the study of the time course of the absorption, distribution, metabolism, and elimination of an administered drug. Thus, it includes the quantitation of such elements of drug bioavailability as tear dilution, drug binding, and vehicle effects; factors affecting corneal absorption and subsequent tissue distribution; dosage form effects; and pathways of elimination. These factors are important because they significantly influence the clinical responses to administered drugs, in some instances to a profound degree. These elements and their clinical implications are discussed along with some recent applications, exemplified with data from studies on frequently prescribed drugs.