fidaxomicin
Brand: Dificid
Prototype Drug
Drug Class: macrocyclic antibiotic
Drug Family: antibiotic
Subclass: narrow-spectrum anti-C. difficile antibiotic
Organ Systems: infectious-diseasegastrointestinal
Mechanism of Action
Inhibits bacterial RNA polymerase by binding the sigma subunit, blocking transcription initiation; structurally distinct from rifamycins with no cross-resistance; minimal systemic absorption ensures high fecal concentrations active against C. difficile.
bacterial RNA polymerase sigma subunit
Indications
- Clostridioides difficile infection (CDI) — preferred over vancomycin for recurrent CDI due to lower recurrence rates
Contraindications
- fidaxomicin hypersensitivity
Adverse Effects
Common
- nausea
- vomiting
- abdominal pain
Serious
- anaphylaxis (rare)
- C. difficile paradoxical flare (extremely rare)
Pharmacokinetics (ADME)
| Absorption | minimal systemic absorption (<1%); achieves high fecal concentrations |
| Distribution | primarily GI tract |
| Metabolism | intestinal hydrolysis to active metabolite OP-1118 |
| Excretion | fecal (>92%) |
| Half-life | 11.7 hours (plasma, though minimal systemic levels) |
| Onset | rapid (within GI tract) |
| Peak | 1–5 hours (minimal plasma levels) |
| Duration | 10-day course |
| Protein Binding | high (systemic fraction highly protein-bound) |
| Vd | very low (minimal systemic absorption) |
Drug Interactions
| Drug / Agent | Mechanism | Severity |
|---|---|---|
| cyclosporine | P-glycoprotein inhibitor may increase systemic fidaxomicin exposure; clinical significance limited by minimal baseline absorption | minor |
Nursing Considerations
- Administer 200 mg orally twice daily for 10 days; may be given with or without food.
- Explain to the patient that fidaxomicin treats the current infection but does not address the underlying risk factors for C. difficile recurrence (ongoing antibiotic use, immunosuppression).
- Continue contact precautions for CDI until diarrhea resolves; C. difficile spores are resistant to alcohol hand sanitizers — perform soap-and-water hand hygiene.
- Monitor for resolution of diarrhea and abdominal symptoms; if symptoms worsen or bloody diarrhea develops, notify prescriber immediately.
Clinical Pearls
- Fidaxomicin's minimal systemic absorption limits its activity to the GI tract, concentrating its effect where C. difficile colonizes; this also means it has essentially no systemic adverse effects.
- Compared to oral vancomycin, fidaxomicin has equivalent cure rates but significantly lower recurrence rates for non-NAP1 strains, making it particularly valuable for patients with recurrent CDI.
Safety Profile
Pregnancy generally-safe
Lactation use-with-caution
Renal Adjustment Not required
Hepatic Adjustment Not required
TDM Not required
Guideline Update pending
Concordance Terms
Cross-referenced clinical concepts — click any term to see all content where it appears.