Challenges in ocular drug delivery

CHALLENGES IN OCULAR DRUG DELIVERY 5.9.2.1 Anatomical and Physiological Considerations... 

Given the considerable challenge of ocular drug delivery, i.e. short contact time and low drug bioavailability, mucoadhesives are attractive excipients in ophthalmic drug formulations. The presence of mucin in the eye allows bioadhesive polymers to thicken the tear film in the front of eye. 

Pepic, I. Lovric, J. Filipovic-Grcic, J. Polymeric micelles in ocular drug delivery Rationale, strategies and challenges. Chem. Biochem. Eng. Q. 2012, 26 (4), 365-377. 

J. J. Yang, H. Ueda, K. Kim, and V. H. Lee. Meeting future challenges in topical ocular drug delivery Development of an air-interfaced primary culture of rabbit conjunctival epithelial cells on a permeable support for drug transport studies. J Control Release 65 1-11 (2000). 

Vandamme TF. (2002). Microemulsions as ocular drug delivery systems Recent developments and future challenges. Progress in Retinal and Eye Research, 21, 15-34. 

The main challenge in ocular delivery is to increase the bioavailability of the drug and its residence time in the cornea, conjunctiva, and epithelia. Nanoscale polymers such as dendrimers can contribute to sustained release of encapsulated drugs at these sites. PAMAM dendrimers have been employed as ophthalmic vehicles in ocular delivery systems with pilocarpine nitrate and tropicamide (Vandamme and Brobeck 2005). 

Due to the lack of activity after oral administration for most peptides and proteins, administration by injection or infusion - that is, by intravenous (IV), subcutaneous (SC), or intramuscular (IM) administration - is frequently the preferred route of delivery for these drug products. In addition, other non-oral administration pathways have been utilized, including nasal, buccal, rectal, vaginal, transder-mal, ocular, or pulmonary drug delivery. Some of these delivery pathways will be discussed in the following sections in the order of the increasing biopharmaceutic challenges to obtain adequate systemic exposure. 

The development of new ocular drug-products, and more sophisticated delivery systems for the effective administration to the patient, pose several technical challenges for the for-mulator. These are discussed in more detail later in this chapter. 

Drug delivery in ocular therapeutics is a challenging problem and is a subject of interest to scientists working in the multidisciplinary areas pertaining to the eye. 

Ophthalmic diseases are most commonly treated by topical instillation of eye drops. These formulations evidence limitations like poor stability and efficacy, reduced cor-neal/scleral permeability, systemic toxicity and lack of compUance [2]. In this sense, the development of effective therapies for visual disorders is of high priority [1], which makes the field of ocular delivery one of the most interesting and challenging areas for pharmaceutical scientists [3]. There has been significant research directed towards the development of new systems for controlled drug delivery in ophthalmology such... 

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