Eye gels for ophthalmic delivery

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.