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New drug index
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
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).
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.
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
demonstrates a post-antibiotic effect vs. C. difficile of 6 - 10 hrs.
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
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 www.fda.gov/medwatch.