According to the Food and Drug Administration, it takes an average of eight years to develop a new drug; drug companies say it can take 15. For every 5,000 new compounds that make it into preclinical testing, only five enter human trials. The costs can be astronomical. Because pharmaceutical companies are loath to invest in a therapy that may never succeed—a particular obstacle in neurology, which includes very rare diseases—many researchers are finding new ways to use drugs already available.

The approach is faster, cheaper, and often remarkably effective, says Robert Baughman, associate director for technology and development at the National Institute for Neurological Disorders and Stroke. “From a combination of clinical observation and understanding of brain biochemistry, we often find that a drug’s activity in one disorder will predict its usefulness in a seemingly unrelated condition,” Baughman says.

The anti-epileptic drug pregabalin, for example, has proven quite effective at treating neuropathic pain. This intense, chronic pain is common in diabetes, AIDS, and spinal cord injury. It results from nerve damage, when cells continue to transmit pain messages indefinitely, and does not respond to conventional analgesics.

Reporting in the November 2006 Neurology, Philip Siddall and colleagues at the University of Sydney, Australia, found that patients with neuropathic pain caused by spinal cord injury reported a significant decrease in pain when given pregabalin twice a day for twelve weeks; patients also reported better sleep and less anxiety.

Another anticonvulsant, gabapentin, has proved useful at treating post-herpetic neuralgia, or shingles (an intensely painful viral infection of sensory nerves), and the neuropathic pain associated with diabetes. Baughman notes that anticonvulsants have the advantage of achieving their primary task quickly.

“If a drug is meant to stop a seizure, you know right away if it works or not,” he says. “Then you have a rationale for testing it in a condition that responds more slowly, such as chronic pain.”

Fast-Acting Antidepressant

Two existing drugs have shown dramatic results in relieving depression. In the August 2006 Archives of General Psychiatry, researchers led by Carlos Zarate, Jr., of the National Institute of Mental Health reported that ketamine, an anesthetic, improved the mood of patients with major depression in as little as two hours.