General Information

Dificid (fidaxomicin) is a narrow-spectrum macrocyclic antibiotic.

Dificid is specifically indicated in adults for treatment of Clostridium difficile-associated diarrhea. To reduce the development of drug-resistant bacteria and maintain the effectiveness of Dificid, it should be used only to treat infections that are proven or strongly suspected to be caused by Clostridium difficile.

Dificid is supplied as a tablet designed for oral administration. The recommended dose is one 200 mg tablet orally twice daily for 10 days with or without food.

Clinical Results

FDA Approval
The FDA approval of Dificid was based on two randomized, double-blinded, non-inferiority trials. The trials were designed to demonstrate the efficacy of Dificid (200 mg twice daily for 10 days) compared to vancomycin (125 mg four times daily for 10 days) in adults with Clostridium difficile-associated diarrhea (CDAD). The primary efficacy endpoints were the clinical response rate at the end of therapy, based upon improvement in diarrhea or other associated symptoms, and sustained clinical response 25 days after the end of treatment. Both endpoints were reached in both trials, showing that Dificid is non-inferior to vancomycin. The clinical response rate for both trials was 88% in the Dificid arms and 86% and 87% in the vancomycin arms. The sustained clinical response was 70% and 72% in the Dificid arms and 57% in the vancomycin arms.

Side Effects

Adverse events associated with the use of Dificid may include, but are not limited to, the following:

• nausea
• vomiting
• abdominal pain
• gastrointestinal hemorrhage
• anemia
• neutropenia

Mechanism of Action

Fidaxomicin is bactericidal against C. difficile in vitro, inhibiting RNA synthesis by RNA polymerases.

Literature References

Louie TJ, Miller MA, Mullane KM, Weiss K, Lentnek A, Golan Y, Gorbach S, Sears P, Shue YK; OPT-80-003 Clinical Study Group Fidaxomicin versus vancomycin for Clostridium difficile infection The New England Journal of Medicine 2011 Feb 3;364(5):422-31

Tannock GW, Munro K, Taylor C, Lawley B, Young W, Byrne B, Emery J, Louie T A new macrocyclic antibiotic, fidaxomicin (OPT-80), causes less alteration to the bowel microbiota of Clostridium difficile-infected patients than does vancomycin. Microbiology 2010 Nov;156(Pt 11):3354-9. Epub 2010 Aug 19

Additional Information

For additional information regarding Dificid or Clostridium difficile-associated diarrhea, please visit the Dificid web page.