New Antibiotic Fights C. diff Infections
Study Shows Fidaxomicin Helps Treat Recurrent C. diff Infections
By Kathleen Doheny
WebMD Health News
Reviewed by Laura J. Martin, MD
40ish woman looking serious

Feb. 2, 2011 -- A new antibiotic, fidaxomicin, is as effective as vancomycin in curing C. diff (Clostridium difficile) infections and may be better at reducing recurrences, new research shows.

''A cure -- that means getting over the diarrhea -- was the same for both, about 90%,'' says researcher Sherwood Gorbach, MD, chief medical officer at Optimer Pharmaceuticals, which funded the study. "However, for recurrences there was a 45% reduction with fidaxomicin [over vancomycin]."

C. diff infections, which often occur after a person has taken antibiotics, affect the gastrointestinal tract and can be deadly. Recurrences are common and troublesome with C. diff infection, seen in 20% or 30% of patients.

In the study, 13.3% of those on fidaxomicin had a recurrence during the four-week follow up, compared to 24% of those on vancomycin.

Infections with C. diff have been on the rise in recent years, with the incidence more than doubling since 1996. According to some estimates, up to 3 million cases of the infection are diagnosed in the U.S. annually.

The infection often occurs in hospitalized patients and in nursing home residents, but can also occur in the community. Recently, a new and more virulent strain has emerged, experts say.

The study is published in the New England Journal of Medicine.
Options for Treating C. Diff

Two medications are typically used for C. diff: metronidazole, which is used ''off-label'' as it is not approved by the FDA for this purpose; and vancomycin, which is FDA approved for treating the infection.

Fidaxomicin is a macrocyclic antibiotic from a new class of antibiotics that targets a narrower range of ''bugs'' and is minimally absorbed by the body.

In the study, 629 adults with symptoms of a C. diff infection and positive results on a stool toxin test were assigned either to take fidaxomicin, 200 milligrams twice a day, or vancomycin, 125 milligrams four times a day. The treatment continued for 10 days.

Researchers compared cure rates in each group. Cure was defined as the resolution of symptoms (diarrhea) and no need for further treatment as of the second day after the end of the 10-day course of medicine.

Gorbach's team also looked at recurrences during a four-week follow-up.

Four weeks is the typical time period in which a recurrence occurs, Gorbach tells WebMD. "We find most people have a recurrence within four weeks. In fact, most have it within two weeks."

With each recurrence, he says, the chance of another recurrence goes up.
Fidaxomicin vs. Vancomycin

The rates of cure were similar -- 88.2% in the fidaxomicin and 85.8% with vancomycin.

But overall, fewer patients treated with fidaxomicin had another bout during the follow-up -- 13.3% vs. 24%.

However, when the researchers looked just at those who had the more virulent strain -- about a third of the patients -- they found the recurrence rates similar between the two medicines -- 24.4% for fidaxomicin and 23.6% for vancomycin.