Medical treatment of glaucoma is evolving to include internal and external drug delivery systems that will ensure patient compliance for long periods.
This article was reviewed by Christophe Baudouin, MD, PhD, FARVO
The best treatment for glaucoma would be efficient, well tolerated over the long and short term, easily used with minimal constrains, affordable, and having increased duration of effect to increase patient compliance. This is a tall order.
One of the biggest problems that physicians face who treat patients with glaucoma is adherence to the treatment regimen. Poor adherence, according to Christophe Baudouin, MD, PhD, FARVO, has an estimated annual cost of $100 to $300 billion in the US, which translates to from 3% to 10% of health care spending.
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So, while uncontrolled IOP and visual field deterioration may be considered disease progression, in reality the patient simply may not be treated properly.
“This is an important issue; but patient education is not always the answer because from 25% to 40% of motivated patients have difficulties or fail to properly instill their drops, said Dr. Baudouin, professor of ophthalmology, head, Department of Ophthalmology III, Quinze-Vingts National Ophthalmology Hospital and director, Team S12, Chemokines and Glaucoma, Vision Institute, University Paris 6, Paris.
Recent developments in glaucoma have seen the introduction of preservative-free formulations designed to decrease side effects and drugs with increasing durations of effectiveness have decreased the number of instillations prescribed as have fixed combinations of drugs, gels, and polymers.
However, new routes and delivery systems may represent the future of glaucoma therapy.
“We may have the choice of administering drugs over or under the conjunctiva or subconjunctivally or intraocularly with drugs implanted in the anterior chamber, intravitreally, or in Schlemm’s canal,” Dr. Baudouin commented.
One such challenge is making sure the correct dose of a drug reliably reaches the targeted tissue.
“Only 10% of eye drops reaches the receptor,” he said. Dr. Baudouin likened the eye a fortress in that all of the ocular structures are barriers to effective drug penetration. “We must overcome this barrier to properly deliver a high or sustained medication dose,” he said.
Nanotechnology one approach
Nanoparticles have been used for more than 10 years, examples of which are cyclosporine and the development of a latanoprost nanoemulsion, both to increase the drug penetration and reduce the amount of the drug in the drop to reduce side effects. The use of gold nanoparticles is also in the development stage to achieve the same goal.
Latanoprost, timolol, and brinzolamide have been tested in nanocarriers with the goals of reducing the concentration and side effects, Dr. Baudouin explained.
Drug penetration has been enhanced using iontophoresis or electroporation with low-voltage current, a technology that has not yet been used in glaucoma. The disadvantage of these approaches is that they do not increase the duration of the treatment for a substantial period of time, he pointed out.