FIDAXOMICIN
Clinical safety rating: caution
Comprehensive clinical and safety monograph for FIDAXOMICIN (FIDAXOMICIN).
Fidaxomicin is an RNA polymerase inhibitor that acts bactericidal against Clostridioides difficile by inhibiting transcription via binding to RNA polymerase, leading to cell death. It has minimal systemic absorption and narrow spectrum of activity.
| Metabolism | Minimally metabolized; primarily excreted unchanged in feces; small amount undergoes hydrolysis to its major metabolite, OP-1118, which has some antibacterial activity. No significant hepatic metabolism via CYP450 enzymes. |
| Excretion | Fidaxomicin is primarily eliminated via fecal excretion as unchanged drug (92%), with minimal renal excretion (<1%). Biliary elimination accounts for a minor fraction. |
| Half-life | Terminal elimination half-life is approximately 11.7 hours (range 8–20 hours) in patients with Clostridium difficile infection, supporting twice-daily dosing. |
| Protein binding | Approximately 86% bound to plasma proteins, predominantly albumin. |
| Volume of Distribution | Volume of distribution is approximately 9 L/kg (range 7–11 L/kg), indicating extensive tissue distribution beyond plasma. |
| Bioavailability | Oral bioavailability is extremely low (<0.5%) due to minimal systemic absorption; acts locally in the gastrointestinal tract. |
| Onset of Action | Clinical response typically observed within 24–48 hours of oral administration due to local action in the colon. |
| Duration of Action | Duration of action persists throughout the 10-day treatment course; sustained fecal concentrations above MIC for C. difficile up to 5 days after last dose. |
| Molecular Weight | 1058.04 |
200 mg orally twice daily for 10 days.
| Dosage form | TABLET |
| Renal impairment | No dose adjustment required for renal impairment, including dialysis. |
| Liver impairment | No dose adjustment required for mild to moderate hepatic impairment (Child-Pugh A or B). Not studied in severe hepatic impairment (Child-Pugh C). |
| Pediatric use | Approved for age ≥6 months: 200 mg orally twice daily for 10 days; for weight <12.5 kg: 160 mg (4 mL suspension) orally twice daily for 10 days. |
| Geriatric use | No dose adjustment required; clinical studies included elderly patients with no differences in safety or efficacy. |
| 1st trimester | No adequate human data; animal studies show no risk at clinically relevant doses. Use only if clearly needed. |
| 2nd trimester | No adequate human data; animal studies show no risk. Consider risk-benefit. |
| 3rd trimester | No adequate human data; minimal systemic absorption suggests low fetal risk. |
Clinical note
Comprehensive clinical and safety monograph for FIDAXOMICIN (FIDAXOMICIN).
| Placental transfer | Minimal; fidaxomicin is poorly absorbed orally and has negligible systemic exposure (<0.1% of dose). Placental transfer is expected to be low. |
| Breastfeeding | Due to negligible oral bioavailability and minimal systemic absorption, fidaxomicin is unlikely to reach significant levels in breast milk or cause adverse effects in nursing infants. Use with caution. |
■ FDA Black Box Warning
None.
| Serious Effects |
Hypersensitivity to fidaxomicin or any component of the formulation
| Precautions | Not effective for systemic infections., May cause hypersensitivity reactions including angioedema and rash., Monitor for development of antibiotic-associated diarrhea due to other pathogens., Use with caution in patients with severe hepatic impairment (not studied). |
| Food/Dietary | No significant food interactions; fidaxomicin may be taken with or without food. Avoid alcohol during treatment as it may exacerbate gastrointestinal side effects. |
| Clinical Pearls |
Loading safety data…
| Lactation Rating |
| L3: Probably Compatible |
| Teratogenic Risk | Fidaxomicin has low systemic absorption; no human pregnancy data available. Animal studies show no teratogenicity at doses up to 20 times the human exposure based on AUC. Risk cannot be excluded, but due to limited systemic exposure, fetal risk is likely low. Use only if clearly needed. |
| Fetal Monitoring | No specific fetal monitoring required due to low systemic absorption. Standard prenatal care. |
| Fertility Effects | No adverse effects on fertility observed in animal studies at clinically relevant doses. |
| Fidaxomicin is minimally absorbed systemically (<1%), resulting in high fecal concentrations. It is bactericidal against Clostridioides difficile (C. diff) and has a narrower spectrum than vancomycin, preserving gut microbiota. Use for initial episode or first recurrence of C. diff infection. Avoid in patients with inflammatory bowel disease due to risk of systemic absorption. |
| Patient Advice | Take fidaxomicin exactly as prescribed, with or without food. · Complete the full 10-day course even if symptoms improve. · Do not take antidiarrheal medications without consulting your doctor. · Contact your healthcare provider if diarrhea worsens or does not improve. · Store tablets at room temperature, away from moisture and heat. |