Fidaxomicin

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Cat Number

API873857626

CAS Number

873857-62-6

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CAS Number

873857-62-6

EINECS

692-555-6

Storage

Store at 2-8°C

Synonyms

Tiacumicin B; Dificid; Dificlir; Lipiarmicin; OPT-80; Difimicin; PAR-101; fidaxomicine

Molecular Formula

C52H74Cl2O18

Molecular Weight

1058

Smiles

CC[C@H]1/C=C(/[C@H](C/C=C/C=C(/C(=O)O[C@@H](C/C=C(/C=C(/[C@@H]1O[C@H]2[C@H]([C@H]([C@@H](C(O2)(C)C)OC(=O)C(C)C)O)O)\\C)\\C)[C@@H](C)O)\\CO[C@H]3[C@H]([C@H]([C@@H]([C@H](O3)C)OC(=O)C4=C(C(=C(C(=C4O)Cl)O)Cl)CC)O)OC)O)\\C

Appearance

White to off-white powder

Melting Point

161°C

Boiling Point

1046.4±65.0°C (Predicted)

Relative Density

1.33

General Description

Fidaxomicin is a macrocyclic antibiotic belonging to the tiacumicin class, produced by the actinomycete Dactylosporangium aurantiacum. Its structure features a 18‑membered macrocyclic lactone ring with a unique glycosylated side chain.

Mechanism of Action

Fidaxomicin inhibits bacterial RNA polymerase by binding to the switch region of the sigma factor, blocking the transcription of DNA into RNA and preventing protein synthesis. This inhibition is specifically bactericidal against Clostridioides difficile, with minimal effect on normal gut flora due to its narrow spectrum. The drug is active against the vegetative form of the bacterium but does not affect spores.

Application

Fidaxomicin is indicated for the treatment of Clostridioides difficile‑associated diarrhea (CDAD) in adults, including severe cases. It is effective against strains with high‑level resistance to metronidazole and vancomycin. The drug has a lower rate of recurrence compared to vancomycin and is used for both initial and recurrent episodes.

Spatial RNA sequencing of fibrotic ileal tissues from Crohn’s disease stricture patients revealed PDGFRB overexpression. High-throughput screening identified fidaxomicin, an FDA-approved drug for C. difficile infection, as a PDGFRB inhibitor. Fidaxomicin reduced collagen and PDGFRB mRNA expression in patient-derived fibroblasts and ileal tissues, and inhibited PDGFRβ and GSK3β phosphorylation. In SAMP1/YitFc mice, oral fidaxomicin reduced ileal fibrosis, effects abolished by Pdgfrb and Gsk3b overexpression. Fidaxomicin inhibits intestinal fibrosis by targeting PDGFRβ/GSK3β signaling.

Fig. 1 Spatial RNA sequencing revealed commonly overexpressed genes in the fibrotic regions of intestinal strictures in CDS patients. (Irwin S, et al., 2025)

References

Irwin S, et al. Fidaxomicin Reduces Collagen Expression in Intestinal Fibroblasts Via Platelet-Derived Growth Factor Receptor Beta and Glycogen Synthase Kinase-3 Beta Inhibition. Gastroenterology. 2025;169(5):925-941.e2.

Using a "DNA to Proteins" affinity purification method, the global regulator MtrA was identified as a positive regulator of fidaxomicin biosynthesis in Actinoplanes deccanensis. Overexpressing mtrA increased fidaxomicin production by 37%. Combining DAP‑seq and RNA‑seq, the authors systematically elucidated MtrA's direct and indirect regulatory roles in primary and secondary metabolism. This provides a new strategy for improving fidaxomicin production.

Fig. 2 Identification of the fadS5R1p-interactive regulator MtrA. (Xie H, et al., 2023)

References

Xie H, et al. Transcriptional regulation of the fidaxomicin gene cluster and cellular development in Actinoplanes deccanensis YP-1 by the pleiotropic regulator MtrA. Microbiol Spectr. 2023;11(6):e0270223.

Does Fidaxomicin require refrigerated storage as a macrolide antibiotic?

Yes, it must be stored at 2-8°C. At room temperature, rapid hydrolysis of the glycosidic bonds occurs, reducing antibacterial activity.

Is Fidaxomicin sensitive to light and moisture during storage?

Yes, it is both photosensitive and hygroscopic. Store in original, tightly sealed, light-resistant containers with desiccant under refrigeration.

What is the stability of Fidaxomicin in tablet formulations with standard excipients?

Yes, when formulated with moisture-protective packaging.

How is the impurity fidaxomicin aglycone (a hydrolysis product) monitored?

This primary degradation product is specifically quantified using a stability-indicating HPLC method, ensuring it remains within ICH limits.