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Antibiotic reduces relapse of C. difficile: study

C. difficile is a common cause of infectious diarrhea in nursing homes and hospitals, and usually occurs in patients who have been taking regular antibiotics for an infection.

Ruth Bonneville

Infectious disease specialists are encouraged by the testing of a new antibiotic to combat C. difficile, a nasty infection that causes diarrhea and has been a scourge in hospitals throughout North America in recent years.

In a trial involving more than 600 patients, fidaxomicin was as effective as the existing treatment in fighting the gut-wrenching infection, but fewer patients had a recurrence.

That's important, experts say, because about 25 to 30 per cent of patients will have a recurrence within 28 days of stopping treatment.

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Fidaxomicin still needs approval from the U.S. Food and Drug Administration and Health Canada. But Andrew Simor, an infectious disease expert who wasn't involved in the research, said it's clearly "an important advance" and a "significant development."

Clostridium difficile is a common cause of infectious diarrhea in nursing homes and hospitals, and usually occurs in patients who have been taking regular antibiotics for an infection. These antibiotics decrease the normal beneficial bacteria in the gut and allow C. difficile bacteria, which are resistant to most antibiotics, to grow uncontrollably.

When these bacteria grow, they produce a toxin that affects the intestinal lining, said Mark Miller, head of infectious diseases and chief of microbiology at Jewish General Hospital in Montreal.

"In the last 30 to 40 years, there's been nothing new for C. difficile treatment," said Dr. Miller, second author of the research paper published Wednesday in the New England Journal of Medicine.

"This is really the first drug to come along to address C. difficile in terms of, 'Can we get a better treatment?'"

The Phase 3 trial of fidaxomicin, the first in a new class of narrow-spectrum macrocyclic antibiotics, compared it to the current treatment vancomycin at 52 sites in the United States and 15 sites in Canada.

Dr. Miller said the drug is taken orally and goes straight to the intestinal tract, working directly on C. difficile in the gut.

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"It's fairly focused so that it works on C. difficile without affecting a lot of the other normal healthy bacteria ... and that's good because it's felt that by keeping the normal flora there, you actually help the person to recover, and not recur," he said.

The study found that fidaxomicin was just as good as vancomycin in eliminating C. difficile at the end of 10 days of treatment - but there was a 45 per cent reduction in recurrences of infection with the new drug.

Dr. Simor, chief of microbiology and infectious diseases at Sunnybrook Health Sciences Centre in Toronto, said it is a good study, but has some limitations. The most severe cases of C. difficile were excluded, so it's not known whether the new drug would be equally effective for those patients.

Follow-up was one month, he noted, and that would capture most, but not, all recurrences.

And finally - and perhaps most importantly - Dr. Simor said that although there was an overall decrease in the recurrence rate, there was no decrease in recurrence if the infection was caused by the more virulent NAP1 strain.

"Anywhere from 30 to 50 per cent of the disease in Canadian hospitals today is caused by the NAP1, and there was apparently no benefit in reducing the recurrence rate," he observed.

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Dr. Miller acknowledged that the recurrence rate was the same as vancomycin for patients with the NAP1 strain.

"Although ... that's a bit of a disappointment, the number of patients with the NAP1-027 infection are still in the minority, so the vast majority of patients, whether they're in Canada, Europe, the United States, are still infected with strains that are not NAP1," he said.

"We expect that most people will benefit from the new drug."

Michael Gardam, medical director of infection prevention and control at the University Health Network in Toronto, also said the data were limited by the fact that severe cases were excluded, and he would like to know if the new antibiotic could help those patients too.

"The ones with the really bad disease, it's horrible - it's a horrible disease for people," he said. "They're in agony, and they can go on to end up having their colons removed as the only way of actually treating them."

But he said it's a good thing that studies are being done on C. difficile because it's gone from being a nuisance to a really serious illness, largely due to NAP1. He estimated that it causes hundreds of deaths each year in Canada.

"Having another antibiotic in your pocket that you could use is always a good thing," he said.

"In places that don't have a lot of NAP1, this study suggests that fidaxomicin would be better."

Christine Lee, an infectious disease specialist at St. Joseph's Healthcare and McMaster University in Hamilton, participated at one of the sites for the clinical trial.

She said C. difficile is one of the challenging hospital-acquired infections.

"Once the patient is infected with this, it's very difficult to cure," she said, adding that the recurrence rate tends to be higher in elderly patients.

She's hopeful about the discovery of a new agent which appears to be promising in terms of reducing recurrence.

"So I'm very excited about it."

The drug was developed by Optimer Pharmaceuticals of San Diego. The cost isn't yet known, Dr. Miller said.

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