August 11, 2009

Contact Lens As Drug Dispenser

Contact lenses are an effective way to deliver drugs for a variety of conditions. And they are more cost effective, too.

Researchers at Children's Hospital in Boston, the Massachusetts Eye and Ear Infirmary and MIT have developed special contact lenses that are able to dispense medication at a steady rate for 30 days. These lenses may eventually become the common way for people to get medication into their eyes, replacing eye drops.

The lenses were tested and shown to work inside containers of liquid. Animal tests are underway, with plans to begin testing in humans soon.

Patients were using an average of 1.8 drops for every drop needed. This is nearly double the dose and uses up a prescription nearly twice as fast.

Drug releasing contact lenses have been around for a while, but there have been problems with their rate of drug delivery. Typically, they would deliver large bursts of the drug at first, followed by steadily decreasing amounts that were too low to be useful. They're supposed to deliver a constant, steady dose. The new lenses accomplish this, partially through use of a two−layer construction. The materials used for both the inner (PLGA) and outer (pHEMA) layers are already approved by the FDA for ocular use.

In laboratory tests, the lenses delivered the antibiotic ciprofloxacin for 30 days, in amounts large enough to kill the bacteria the drug is supposed to be killing. The FDA currently limits disposable contact lenses to 30 days of use.

The researchers expect the primary application of the lenses to be in patients with problems such as glaucoma and dry eye. They note that because of tearing and blinking, as little as 1−7% of an eye drop dose may end up being absorbed by the eye.

The results of this study were published in the July 2009 issue of Investigative Ophthalmology & Visual Science.

Another recent study shows just how difficult it can be for people to get eye drops into their eyes. They think they're doing a good job, but they're not.

The Johns Hopkins' study was of 139 patients with glaucoma or ocular hypertension who administered their own eye drops. Over 90% of them reported no problem in doing so. Video recordings of the patients disagreed. Patients were using an average of 1.8 drops for every drop needed. This is nearly double the dose and uses up a prescription nearly twice as fast. And only 20−30% of the patients were able to get the drops into their eye without touching the eye with the bottle. Large bottles were more difficult to use than small ones.

Less than 2% of the people washed their hands before putting the drops in. The camera doesn't lie.

A contact lens that dispenses eye drops properly for a month sounds like quite an improvement, if it works as advertised.

The study on just how difficult it is to get drops into the eye was published in the June 2009 issue of Archives of Ophthalmology.

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