Eye gels for ophthalmic delivery

Abstract

The eye’s unique physiology, biochemistry and anatomy present the pharmaceutical scientist with a number of drug delivery problems. Historically, eye drops and eye ointments have been the formulations of choice for delivering drugs to the anterior section of the eye. These formulations have a very poor bioavailability, typically in the region of 5%. By incorporating a polymer to create an ophthalmic gel, a viscosity-modified formulation can be produced, which has the potential to prolong residence of the drug at the desired location. Many of these polymers display bioadhesion, further improving the bioavailability of the active agent. This review investigates in situ gels in particular, which are instilled as a liquid but which become gels through a physical stimulus.

Keywords:

• bioadhesion
• eye
• eye gel
• in situ
• ocular
• ophthalmic
• rheology

Financial & competing interests disclosure

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

No writing assistance was utilized in the production of this manuscript.

Key issues

• The eye is extremely difficult to target due to numerous protective mechanisms, including blinking, tear production and tight cell junctions.

• Eye drops have around 1–2 min of residence at the target tissues before draining through the nasolacrimal ducts.

• Ocular bioavailability is typically around 5% with traditional eye drops.

• Traditional ocular formulations consist of aqueous solutions or ointments, each with serious drawbacks.

• Hydrogels can be incorporated to produce viscosity-modified solutions.

• Pseudoplastic rheology is ideal for ophthalmic formulations.

• In situ gels are instilled as a solution and gel upon contact with the eye through a physiological trigger.

• Bioadhesion is a useful property, which can be exploited for the improvement of ophthalmic bioavailability.

• Gels can be stabilized using preservatives, salts and buffers.