FDA Panel Gives New Antibiotic Fidaxomicin 2 Thumbs Up

Fran Lowry

April 05, 2011

April 5, 2011 — The experimental antibiotic fidaxomicin (Optimer Pharmaceuticals Inc) has won a hearty endorsement from the US Food and Drug Administration (FDA) Anti-Infective Drugs Advisory Committee for the treatment of life-threatening Clostridium difficile–associated diarrhea.

The committee unanimously agreed that fidaxomicin was safe and effective, although a few panel members voiced concerns about safety in pregnant women, the elderly, and people with a compromised immune system in the discussion that followed the vote. Some of the panel were also concerned about gastrointestinal bleeding, which occurred more often with fidaxomicin than with vancomycin.

Clostridium difficile

The positive reception was forecast last week when FDA reviewers released documents stating that fidaxomicin worked as well as its comparator, the older antibiotic vancomycin, in fighting C difficile infections.

According to FDA documents, fidaxomicin, which Optimer plans to market as Dificid, is a macrolide antibacterial with an 18-membered ring that is microbiologically active against C difficile. It has a narrow-spectrum antibacterial profile, has bactericidal activity against C difficile, is poorly absorbed, and exerts its activity in the gastrointestinal tract.

The panel thought the 2 studies presented by Optimer were very well done.

"I voted yes because the trials were rigorously done," said Yu Shyr, PhD, from Vanderbilt University School of Medicine, Nashville, Tennessee, who was one of the statisticians on the panel.

William Hasler, MD, professor of internal medicine at the University of Michigan, Ann Arbor, said the data were strong. "In fact," he said, "I think the data suggests this drug is superior to vancomycin." He added that he had some minor concerns about the risks of gastrointestinal bleeding and leukopenia, "but I believe these are relatively minor and can be followed postmarketing."

The acting chair of the committee, Matthew Goetz, MD, professor at the David Geffen School of Medicine at the University of California, Los Angeles, added that he too was concerned about leukopenia. Although this concern did not prevent him from voting for approval, leukopenia is something that warrants further observation, he said.

Several panel members were pleased that Optimer had considered the pediatric age group. "Undoubtedly it will be used in that population, and I applaud the company for having a plan in place for looking at pediatric patients," said Sheldon L. Kaplan, MD, professor at Baylor College of Medicine in Houston, Texas.

Archana Chatterjee, MD, PhD, professor of pediatrics at Creighton University School of Medicine in Omaha, Nebraska, noted that C difficile–associated diarrhea, although clearly a significant problem in adults (especially the elderly), is increasingly becoming a concern in children.

"These are the patients I care for," she said. "For the first time I have come to this committee meeting and I do not have to plead for a plan for a formulation for children, so I congratulate that company for having a plan for them."

FDA Anti-Infective Drugs Advisory Committee; Hilton Washington, DC; Silver Spring, Maryland; April 5, 2011.

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