Review of ophthalmic drug delivery by contact lenses

Ophthalmic drugs are almost exclusively delivered through eye drops in spite of several deficiencies including low bioavailability and poor compliance. Contact lenses are ideally suited for delivery of drugs to the anterior chamber because of the placement directly on the cornea which results in a high bioavailability of at least 50 % compared to about 1–5 % for eye drops. The ten-fold increase in bioavailability reduces the amount of drug delivered, which in turn reduces the systemic loss of the drug, thereby reducing the potential for side effects. Additionally contact lenses can provide a most uniform release profile compared to the pulsatile delivery with eye drops, which can potentially result in improved therapeutic outcomes. Finally drug delivery via extended wear contact lenses can significantly improve the compliance. In spite of all these benefits, contact lenses are not yet available as drug delivery vehicles mainly because the earlier lens designs were not optimized for drug delivery. The interest in developing contact lenses for drug delivery has significantly increased in the last decade as several new techniques have been developed for designing contact lenses for extended drug delivery. The latest studies show that contact lenses can achieve extended release of a few weeks without any significant impact on critical lens properties. Also in vivo animal studies have proven safety, efficacy and increased bioavailability compared to eye drops. The future appears promising for drug eluting contact lenses but several challenges remain to be overcome regarding processing and storage issues, lack of use in the elderly population, regulatory issues, high costs of clinical studies and cost-benefit analysis.