WEDNESDAY, Feb. 2 (HealthDay News) -- Late-stage clinical trials of a new antibiotic for the increasingly common intestinal infection Clostridium difficile, which is especially lethal to the elderly, suggest it prevents recurrence far better than currently used medications.

Researchers tested the new drug, fidaxomicin, against vancomycin, a powerful drug often prescribed to C. difficile patients. These cases often involve virulent diarrhea and colon inflammation that proves fatal to an estimated 5,000 Americans each year, according to federal statistics.

People over age 65, especially those in hospitals and nursing homes, are more vulnerable to the infection, which experts estimate strikes up to 3 million Americans annually, many of whom have taken broad-spectrum antibiotics to treat other illnesses.

Among the 629 patients studied, fidaxomicin was associated with a 45 percent lower rate of recurrence than vancomycin, which researchers said was due to fidaxomicin's ability to precisely target C. difficile bacteria in the gut. Vancomycin has a similar clinical cure rate, but it kills more "good" intestinal bacteria bugs that help keep C. difficile at bay, explained study co-author Dr. Sherwood Gorbach.

"It's virtually impossible to beat vancomycin as a cure, but [using fidaxomicin] we could beat it with recurrence," said Gorbach, professor of medicine, immunology, molecular biology and microbiology at Tufts University School of Medicine in Boston.

"Fidaxomicin does kill the bug, but in terms of recurrence, it doesn't disturb the normal balance of flora in the intestines," he said. "This drug should actually save lives."

The study was funded by Optimer Pharmaceuticals, which is developing fidaxomicin, and is published in the Feb. 3 issue of the New England Journal of Medicine.

While vancomycin is often used as a last-resort antibiotic to treat drug-resistant infections -- an emerging public health menace -- fidaxomicin was not developed because C. difficile is becoming resistant to vancomycin or metronidazole, the standard drugs used for milder cases, Gorbach noted.

"The reason for failures is not resistance," he said. "Vancomycin and fidaxomicin both have a 10 percent failure rate. It may be that the spores don't get killed very easily and allow for this disease to continue. It's being called the hospital 'superbug' now."

Enrolled at 52 sites in the United States and 15 in Canada, participants in the phase 3 clinical trial were classified according to whether their current C. difficile infection was the first or second episode. Patients took either fidaxomicin (200 mg twice daily) or vancomycin (125 mg four times daily) orally for 10 days and were followed afterward to determine if their diarrhea had resolved.

A recurrence was defined by the reappearance of more than three diarrheal stools per 24-hour period within four weeks after completion of the drug therapy.

Not only was the recovery time faster among those who took fidaxomicin, but nearly 75 percent recovered without a recurrence, compared to 64.1 percent for the vancomycin patients.

"The people who've had this disease generally say it's the worst disease they've ever had," Gorbach said. "Because [fidaxomicin] decreases recurrences by 45 percent -- and recurrences usually require another hospital stay -- it will actually save money."

Dr. Clifford McDonald, chief of the prevention and response branch of the U.S. Centers for Disease Control and Prevention's division of healthcare quality, said the lower recurrence rate of highly contagious C. difficile associated with fidaxomicin could also lower the transmission rate among patients.

"This does seem like a pretty strong result scientifically," McDonald said. "Hopefully we'll see more antibiotics like this."

McDonald also pointed out that fecal transplants -- a novel therapy for C. difficile that helps restore beneficial intestinal bacteria levels by infusing patients with a stool slurry from a healthy donor -- goes hand-in-hand with efforts to develop antibiotics that destroy fewer of these bacteria.

"Antibiotics do collateral damage. They're not safe to bacteria that have been good to us all along," McDonald said. "I think there's a growing realization that we're not just mammals, but mammals with bacteria on us, and the two co-exist in health."

The U.S. Food and Drug Administration is expected by the end of May to decide if fidaxomicin will go to market later this year, Gorbach said. He and other team members asked for fast track consideration of the drug, saying it meets an unmet need and should be given rapid deliberation.

More information

Find out more about C.difficile at the U.S. National Library of Medicine.