Drug Delivery by Contact Lens in Spontaneously Glaucomatous Dogs

Purpose: The efficacy of ophthalmic drug delivery through contact lenses in animal model was explored to evaluate its potential for serving as an alternative to eye drops, which are inefficient vehicles for delivering ophthalmic drugs. Methods: The efficacy of timolol delivered via contact lenses was compared to eye drops in beagle dogs that suffer from spontaneous glaucoma. Experiments were conducted with NIGHT & DAY (TM) silicone hydrogel contact lenses and NIGHT & DAY (TM) loaded with vitamin E, which was included in the lens to extend the release duration of the drug. Timolol was loaded into contact lenses by soaking in drug/phosphate buffered saline solution, and the drug-loaded lenses were subsequently inserted in one of the eyes, with the other eye serving as control. The lenses were replaced every 24 hours, and the pharmacodynamics of intraocular pressure (IOP) and pupil size were monitored in both eyes. Results: The IOP reduction from baseline by NIGHT & DAY (TM) (5.02 +/- 0.83 mmHg) was comparable with that by eye drops with similar drug dosing (4.64 +/- 0.41 mmHg). In addition, lenses with one-third of the drug loading as eye drops resulted in the similar IOP reduction, suggesting higher bioavailability for contact lenses compared to eye drops. Inclusion of vitamin E into the lenses did not improve the IOP reduction. The IOP in the untreated eye also decreased from baseline for eye drops (3.17 +/- 0.42 mmHg) but it remained relatively unchanged with treatments based on lenses, suggesting reduction in systemic absorption for delivery of drugs by contact lenses. Conclusions: Ophthalmic drug delivery through contact lenses increases bioavailability and reduces systemic drug uptake.