DIFICID
Clinical safety rating: caution
Comprehensive clinical and safety monograph for DIFICID (DIFICID).
Fidaxomicin is a macrocyclic antibiotic that inhibits bacterial RNA polymerase, leading to RNA synthesis inhibition and cell death. It is bactericidal against Clostridioides difficile and has minimal systemic absorption.
| Metabolism | Fidaxomicin is minimally metabolized; hydrolysis of the macrocyclic ring occurs in the gastrointestinal tract, with little systemic metabolism. CYP3A4 is not significantly involved. |
| Excretion | Fecal (primarily as unchanged drug, ~44% of dose); renal (~1.6% unchanged, <1% as metabolites); biliary (minor). |
| Half-life | 11.7 hours (terminal half-life in healthy subjects); supports twice-daily dosing. |
| Protein binding | 92% to 96% (mainly to albumin). |
| Volume of Distribution | 8.8 to 12.5 L/kg (indicating extensive tissue distribution, especially into intestinal mucosa). |
| Bioavailability | Oral: ~2% (absorbed, but systemic exposure low; primarily acts locally in gut). |
| Onset of Action | Not applicable orally; clinical response observed within 72 hours of initiating therapy. |
| Duration of Action | Treatment course is 10 days; bacteriostatic effect persists while drug concentrations exceed MIC for C. difficile. |
200 mg (tablet) orally twice daily for 10 days.
| Dosage form | FOR SUSPENSION |
| Renal impairment | No dose adjustment required for any degree of renal impairment, including hemodialysis. |
| Liver impairment | No dose adjustment required for mild, moderate, or severe hepatic impairment (Child-Pugh A, B, or C). |
| Pediatric use | Approved for pediatric patients ≥6 months of age: 200 mg (tablet) or 200 mg/100 mL oral suspension (5 mg/mL) twice daily for 10 days. Weight-based dosing: 10 mg/kg (max 200 mg per dose) orally twice daily for 10 days. |
| Geriatric use | No dose adjustment required based on age. Monitor renal function and electrolytes if concomitant use of diuretics or NSAIDs; otherwise, same as adult dosing. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for DIFICID (DIFICID).
| Breastfeeding | Fidaxomicin is minimally absorbed systemically (<0.1%) after oral administration; excretion into breast milk is negligible. M/P ratio not determined. Considered compatible with breastfeeding due to very low oral bioavailability and lack of systemic effects in infant. |
| Teratogenic Risk | DIFICID (fidaxomicin) is not teratogenic in animal studies at doses up to 10 times the human exposure based on AUC. No adequate human studies in pregnancy; FDA Category B. Risk cannot be ruled out for first trimester, but potential benefits may warrant use in pregnant women for severe C. difficile infection. |
■ FDA Black Box Warning
None.
| Serious Effects |
["Hypersensitivity to fidaxomicin or any component of the formulation"]
| Precautions | ["Hypersensitivity reactions including angioedema have been reported","Not effective for systemic infections due to minimal absorption","Monitor for development of antimicrobial resistance","Use with caution in patients with severe hepatic impairment (Child-Pugh C) due to lack of data"] |
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| Fetal Monitoring | No specific monitoring required beyond standard C. difficile infection management. Monitor for diarrhea resolution, adverse effects (nausea, vomiting, abdominal pain), and signs of C. difficile recurrence. |
| Fertility Effects | No human studies on fertility. Animal studies up to 2000 mg/kg/day did not demonstrate impaired fertility or reproductive performance. No known effects on human fertility. |