For research use only.

Catalog No.S4227 Synonyms: OPT-80, PAR-101

4 publications

Fidaxomicin Chemical Structure

CAS No. 873857-62-6

Fidaxomicin (OPT-80, PAR-101) is a narrow spectrum macrocyclic antibiotic that inhibits RNA polymerase sigma subunit.

Selleck's Fidaxomicin has been cited by 4 publications

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Biological Activity

Description Fidaxomicin (OPT-80, PAR-101) is a narrow spectrum macrocyclic antibiotic that inhibits RNA polymerase sigma subunit.
RNA polymerase [1]
In vitro

Fidaxomicin acts as a RNA polymerase inhibitor by binding to the DNA template–RNA polymerase (RNAP) complex prior to the formation of the open RNAP-DNA complex in which transcription is initiated. Therefore it will inhibit protein synthesis. As a result, apoptosis is triggered in susceptible organisms such as C. difficile. [1]

In vivo The minimum inhibitory concentration for 90% of organisms for fidaxomicin against C. difficile is 0.9978 to 2 μg/mL. Fidaxomicin is not systemically absorbed as shown by a plasma concentrations below the lower limit of quantification after single-dose or multiple-dose. In contrast, fecal concentrations of fidaxomicin are much higher and are concentration-dependent. Cmax = 2 hours; Tmax = 5.2 ng/mL; AUC = 14 ng•hr/mL. Fidaxomicin is hydrolyzed by gastric acid or intestinal microsomes into a less active metabolite (OP-1118). The cytochrome enzyme system are not involved in the metabolism of fidaxomicin. [1]


Solubility (25°C)

In vitro DMSO 100 mg/mL (94.51 mM)
Water Insoluble
Ethanol Insoluble

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Chemical Information

Molecular Weight 1058.04


CAS No. 873857-62-6
Storage powder
in solvent
Synonyms OPT-80, PAR-101
Smiles CCC1C=C(C(CC=CC=C(C(=O)OC(CC=C(C=C(C1OC2C(C(C(C(O2)(C)C)OC(=O)C(C)C)O)O)C)C)C(C)O)COC3C(C(C(C(O3)C)OC(=O)C4=C(C(=C(C(=C4O)Cl)O)Cl)CC)O)OC)O)C

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Clinical Trial Information

NCT Number Recruitment interventions Conditions Sponsor/Collaborators Start Date Phases
NCT04138706 Recruiting Drug: Vancomycin|Drug: Placebos Clostridium Difficile Infection McGill University Health Centre/Research Institute of the McGill University Health Centre|Canadian Institutes of Health Research (CIHR) November 19 2020 Phase 4
NCT02437591 Completed Drug: fidaxomicin Inflammatory Bowel Disease (IBD)|Clostridium Difficile Infection (CDI) Astellas Pharma Europe Ltd.|Astellas Pharma Inc August 13 2015 Phase 4
NCT02395848 Recruiting Drug: Fidaxomicin Clostridium Difficile Infection McMaster University|Vancouver Island Health Authority July 2015 Phase 3

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