The drug, minocycline, was tested on human volunteers with amyotrophic lateral sclerosis (ALS), as Lou Gehrig's is called, and doctors are testing it on several other diseases of the nervous system.
These trials were launched after tests on lab-dish cells and on mice engineered to have ALS symptoms suggested minocycline could inhibit inflammation and apoptosis -- the process by which nerve cells are ordered to commit suicide.
But in a study published by The Lancet Neurology, US researchers found that ALS patients who took minocycline deteriorated 25-percent faster than counterparts who took a dummy lookalike pill, called a placebo.
"Our finding that minocycline has a harmful effect on patients with ALS has implications for trials of minocycline with other neurological disorders, and for how potential neuroprotective agents are screened for us in patients with ALS," says the study, lead-authored by Paul Gordon of New York's Columbia University.
Minocycline is a second-generation, broad-spectrum member of the tetracycline family, used in a wide range of bacterial infections.
Lou Gehrig's is a currently incurable but also enigmatic disease. It occurs when nerve cells die out, leaving the brain less and less able to control muscles and leading ultimately to paralysis.
Only about 10 percent of patients have a known family history of ALS, which thus causes the finger of blame to point at environmental factors.
Gordon's team enrolled 412 ALS patients, who were randomly assigned to receive a placebo or minocycline in escalating doses of up to 400 milligrams per day for nine months.
It was a Phase III trial, the widest, final step in a process to see whether a new treatment is safe and effective.
Patients were assessed according to standard measurements for coordination and muscle strength, as well as a "quality of life" questionnaire.
Several Phase II and Phase III trials are either planned or underway to look at minocycline's effect on Huntington's disease, stroke, dementia and multiple sclerosis, their paper said.