Researchers have discovered a new method for delivering drugs to the eye using biodegradable polymer nanoparticles that promise controlled release and better bioavailability than eye drops.
A team of scientists at the University of Portsmouth, led by biomaterials and drug delivery expert John Tsibouklis, have found that biodegradable polymers can be combined with drugs in such a way that the medicine is released into the eye in a very precise and controlled manner.
Although easy to use, eye drops have many disadvantages, two main ones being the need to administer drops regularly and too little of the drug getting to areas of the eye most in need.
The common alternative to eye drops, ophthalmic inserts, achieve sustained drug delivery but suffer from limitations as they are difficult to insert, easy to misapply and are expensive to manufacture.
Very few new ophthalmic drug delivery systems have been commercialised so far, but current research on polymeric systems holds considerable promise, the researchers claim.
Certain polymers are already used as carriers or sustained release vehicles, while smart hydrogels, that react to disease-specific environmental triggers or chemical signals to effect drug release, are emerging as components of a new generation of therapeutics
Thus, the formulation of biodegradable polymers as colloidal systems holds significant promise for ophthalmic drug delivery, since it is suitable for poorly water-soluble drugs and would allow drop-wise administration while maintaining the drug activity at the site of action.
"The drug's release can be timed so it is constant, cyclic or triggered by an environmental or chemical signal, and the drug delivering polymer can be broken down naturally by the body when it is no longer needed," Tsibouklis said.
Furthermore, surface-modified nanoparticulate carriers may be used to accommodate a wide variety of actives.
Nonetheless, major developmental issues have to be resolved, including formulation stability, particle size uniformity, control of drug release rate and large-scale manufacture of sterile preparations.
At present, copolymer vesicles and tubules and thermoresponsive polymeric micelles have been investigated as intelligent targeted carrier systems, whilst the versatility of polymers is turned to account in the design of new prodrugs.
These approaches await validation in drug release ophthalmic applications and most probably a combination of technologies holds the key to success, the researchers believe.
Indeed, Tsibouklis claims progress in the characterisation of ocular enzyme systems and cellular transporters is likely to make transporter/receptor mediated ophthalmic drug delivery a viable approach.
Since drugs can be covalently coupled to the side chain of amino acids, making them recognizable by specific transporters, the broad substrate specificity and concentrative ability of amino acid transporters expressed in the eye may prove effective delivery systems for a wide variety of actives.