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Initial U.S. approval: 2011
To reduce the development of drug resistant bacteria and maintain the effectiveness of DIFICID and other antibacterial drugs, DIFICID should be used only to treat infections that are proven or strongly suspected to be caused by Clostridium difficile.

DIFICID (fidaxomicin) is a macrolide antibacterial drug for oral administration.

DIFICID tablets (200 mg) are film-coated and contain the following inactive ingredients: microcrystalline cellulose, pregelatinized starch, hydroxypropyl cellulose, butylated hydroxytoluene, sodium starch glycolate, magnesium stearate, polyvinyl alcohol, titanium dioxide, talc, polyethylene glycol, and lecithin (soy).

Clinical pharmacology


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

Spectrum of Activity

Fidaxomicin is a fermentation product obtained from the Actinomycete Dactylosporangium aurantiacum. In vitro, fidaxomicin is active primarily against species of clostridia, including Clostridium difficile.

Mechanism of Decreased Susceptibility to Fidaxomicin
In vitro studies indicate a low frequency of spontaneous resistance to fidaxomicin in C. difficile (ranging from <1.4 x 10-9 to 12.8 x 10-9). A specific mutation (Val-ll43-Gly) in the beta subunit of RNA polymerase is associated with reduced susceptibility to fidaxomicin. This mutation was created in the laboratory and seen during clinical trials in a C. difficile isolate obtained from a subject treated with DIFICID who had recurrence of CDAD. The C. difficile isolate from the treated subject went from a fidaxomicin baseline minimal inhibitory concentration (MIC) of 0.06 mcg/mL to 16 mcg/mL.

Cross-Resistance/Synergy/Post-Antibiotic Effect
Fidaxomicin demonstrates no in vitro cross-resistance with other classes of antibacterial drugs. Fidaxomicin and its main metabolite OP-1118 do not exhibit any antagonistic interaction with other classes of antibacterial drugs. In vitro synergistic interactions of fidaxomicin and OP-1118 have been observed in vitro with rifampin and rifaximin against C. difficile (FIC values ≤0.5). Fidaxomicin demonstrates a post-antibiotic effect vs. C. difficile of 6 - 10 hrs.

Susceptibility Testing
The clinical microbiology laboratory should provide cumulative results of the in vitro susceptibility test results for antimicrobial drugs used in local hospitals and practice areas to the physician as periodic reports that describe the susceptibility profile of nosocomial and community acquired pathogens. These reports should aid the physician in selecting appropriate antimicrobial drug therapy

Indications and usage 

DIFICID is a macrolide antibacterial drug indicated in adults (≥18 years of age) for treatment of Clostridium difficile-associated diarrhea




DIFICID should not be used for systemic infections.

Development of Drug Resistant Bacteria: Only use DIFICID for infection proven or strongly suspected to be caused by C. difficile.

Pediatrics: The safety and effectiveness of DIFICID has not been studied in patients <18 years of age.

Adverse reactions

The most common adverse reactions are nausea (11%), vomiting (7%), abdominal pain (6%), gastrointestinal hemorrhage (4%), anemia (2%), and neutropenia (2%).
To report SUSPECTED ADVERSE REACTIONS, contact Optimer Pharmaceuticals at 1-855-DIFICID (1-855-343-4243) or FDA at (1-800-FDA-1088) or

Dosage and administration 

One 200 mg tablet orally twice daily for 10 days with or without food .

How supplied

Film-coated tablets: 200 mg


Package Insert data: 
Manufactured for Optimer Pharmaceuticals, Inc., San Diego CA 92121 by Patheon, Inc.

DIFICID™ is a trademark of Optimer Pharmaceuticals, Inc.
Product protected by US Patent Nos. 7,378,508; 7,507,564; 7,863,249; and 7,906,489

Optimer Pharmaceuticals, Inc.
10110 Sorrento Valley Road, Suite C
San Diego, CA 92121
(858) 909-0736

Copyright ® Optimer Pharmaceuticals, Inc.
All rights reserved.

NDC 52015-080-01
20 tablets
Rx only

(fidaxomicin) tablets
200 mg


National Institutes of Health, U.S. National Library of Medicine, DailyMed Database.
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DIFICID™ (fidaxomicin) tablet