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Loud, concussive explosions on the battlefield may last only a few seconds, but many soldiers returning from combat in the Middle East are experiencing lingering symptoms that cause them to perceive sounds even when it is quiet. Doctors can do little to treat the problem—typically described as a ringing in the ears—because they lack an effective way of delivering medication to the inner ear. That could change in a few years, in the form of an implantable polymer-based microscale drug-release system that delivers medicine to the inner ear.
Called tinnitus, the condition afflicts at least one in every 10 American adults and is the most common disability among Afghanistan and Iraq war veterans, according to the U.S. Department of Veterans Affairs (VA). Up to 40 percent of all veterans may be suffering from tinnitus, and the VA spends about $1 billion annually on disability payments for tinnitus, according to a study published last year in Nature. (Scientific American is part of Nature Publishing Group.)
To address the problem, the U.S. Department of Defense has commissioned Draper Laboratory in Cambridge, Mass., to spend the next year fleshing out a concept for a small delivery device inserted near the membrane-covered window—no more than three millimeters in diameter—separating the middle ear from the inner ear. Once at the membrane the device (essentially a polymer capsule, although Draper is not developing any of medicines that might be placed inside) would release a drug into the cochlea, the tubular organ residing in the inner ear that enables us to hear. The plan is to embed wireless communications into the capsule so that a patient or doctor can control the dosage. After the capsule finishes delivering its supply of drugs, it would dissolve.
Although Draper's project is still in the very early stages and years away from any clinical testing, it holds more promise than many of today's most common approaches to tinnitus treatment, which include deep breathing, using background noise to drown out the ringing or simply learning to ignore the bothersome sound. Steroids injected into the eardrum have shown some promise in helping patients with certain hearing and balance disorders, but the ear begins eliminating these drugs through the eustachian tube (a passageway in the middle ear that acts as a pressure equalizer) as soon as the patient talks, swallows or even sits up. As a result, the patient must endure several injections into their ear and remain immobilized for a time after each injection to get any relief from the malady.
"By and large there aren't that many good ways to treat tinnitus," says Lloyd Minor, provost and senior vice president for academic affairs at Johns Hopkins University. Draper's work "is potentially a novel way of delivering drugs to treat tinnitus. In general, we don't have the types of drug-delivery systems that we would like to get medication into the inner ear."
NeuroSystec Corp. is developing a neuro-active agent designed to calm the hyperactive nerves responsible for cochlear tinnitus. The Valencia, Calif., biotech start-up has licensed an osmotic pump from Durect Corp. in Cupertino, Calif., a company working on a number of drug delivery mechanisms for various parts of the body, including the inner ear.
Other advanced approaches of addressing tinnitus have been in the works for years, but most are still not ready for the market. Otonomy, Inc., in San Diego is testing a sustained release dexamethasone (a type of steroid) gel that would be injected into the middle ear, where it would stay in place, dissolving slowly and delivering treatments for hearing and balance disorders. MicroTransponder, a medical device company spun out from the University of Texas at Dallas in 2007, is looking to broaden the use of its implanted wired neuro-stimulation system for treating epilepsy to likewise help tinnitus patients.
The neuro-stimulation approach shows greater promise than those based on delivering medication to the inner ear at this time, says Michael McKenna, an otologist and neurologist at Massachusetts Eye and Ear in Boston. Targeted drug therapy is of questionable benefit because tinnitus comes from a variety of causes—including age-related hearing loss, traumatic ear injuries or circulatory system disorders—and has varying degrees of severity, he adds.
Perhaps some combination of all these efforts will end up delivering the relief that tinnitus sufferers seek. "Nothing really has been a panacea, so there is the need for further technological development," Minor says. If Draper's technology "works in the way they're hoping it will work, it will potentially be a big advance for the field."