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Editors Selection IGR 19-3
Medical Treatment: Prolonged Drug Delivery
Comment by Eytan Blumenthal on:
61390 Dual drug delivery from vitamin E loaded contact lenses for glaucoma therapy, Hsu KH; Carbia BE; Plummer C et al., European Journal of Pharmaceutics and Biopharmaceutics, 2015; 94: 312-321
Compliance and side-effects are two notorious drawbacks of medical therapy for glaucoma. 'Moving the patient out of the loop' in the sense that drug delivery will not depend on a periodic action performed by the patient is high on our wish-list for improving glaucoma care. Various approaches have been suggested and tried, including inserts and intraocular slow-release devices.
Hsu et al. present a study in which two commonly used drugs, timolol and dorzolamide, often prescribed in combination, were simultaneously loaded onto a contact lens that was pre-loaded with vitamin E.
The presence of vitamin E within the contact lens serves to dramatically increase the duration of drug release The desired decrease in the drug transport rate is achieved by an increase in the diffusion path length in the lens matrix. While drug-soaked contact lenses will release the medication for a period of up to a few hours, the incorporation of vitamin E increased this active period to two days. Vitamin E in this case serves as a diffusion barrier while retaining transparency. Incorporation of vitamin E into the contact lens increased the release duration 35- and 14-fold for timolol and dorzolamide, respectively. Of note, and as yet unexplained, when both drugs were soaked in the same lens, the release duration further increased 1.7- and 1.2-fold. This phenomenon is speculated to be perhaps secondary to a timolol-dorzolamide drug interaction within the contact lens.
The presence of vitamin E within the contact lens serves to dramatically increase the duration of drug release
The approach presented in this study removes the burden of drop administration, for the duration that the contact lens is in the eye, but not the compliance needed to place and replace the contact lens periodically (in our case, every two days). In this study, commercially available (standard) soft contact lenses were 'loaded' with IOP-lowering drugs.
These Vitamin E-timolol-dorzolamide pre-loaded lenses were studied on Beagle dogs harboring primary open-angle glaucoma. In comparison to the control group that received standard drop therapy, the group receiving the contact lens therapy enjoyed a stable IOP reduction that lasted as long as a week and more from a single contact lens.
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