Macrocyclic antibiotic (narrow-spectrum) Pregnancy: eMC §4.6: there are no data available from the use of fidaxomicin in pregnant women. Animal studies did not indicate direct or indirect harmful effects with respect to reproductive toxicity. As a precautionary measure it is preferable to avoid the use of fidaxomicin during pregnancy. It is unknown whether fidaxomicin and its metabolites are excreted in human milk; although no effects on breastfed infants are anticipated because systemic exposure is low, a risk cannot be excluded, so a decision must be made whether to discontinue breast-feeding or to discontinue/abstain from fidaxomicin, taking account of the benefit of breast-feeding for the child and of therapy for the woman.

Fidaxomicin

Brand names: Dificlir

Fidaxomicin is a macrocyclic antibacterial used specifically for the treatment of Clostridioides difficile infection.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: 200 mg (one tablet) twice daily (once every 12 hours) for 10 days

Route: Oral - the film-coated tablets should be administered whole with water and can be taken with or without food

Frequency: Twice daily (once every 12 hours)

eMC §4.2 (Fidaxomicin 200 mg film-coated tablets). This is the standard dosing regimen. EXTENDED-PULSED DOSING (alternative regimen in §4.2): 200 mg twice daily on days 1-5, no tablet on day 6, then 200 mg once daily on alternate days for days 7-25. MISSED DOSE: take as soon as possible, or if it is nearly time for the next dose, skip the tablet altogether. Fidaxomicin 40 mg/mL granules for oral suspension may be used in adult patients with difficulty swallowing tablets. ELDERLY: no dose adjustment is considered necessary. HEPATIC IMPAIRMENT: no dose adjustment is considered necessary, but because of limited clinical data use with caution in moderate to severe hepatic impairment. Use with caution in patients with pseudomembranous colitis and in fulminant or life-threatening C. difficile infection (limited clinical data). Fidaxomicin should only be used for C. difficile infection - it is not expected to be effective for other types of infection because of minimal systemic absorption (US §5.2). PAEDIATRIC: eMC §4.2 recommends 200 mg twice daily (once every 12 hours) for 10 days in paediatric patients weighing at least 12.5 kg, using either the film-coated tablets or the granules for oral suspension - this is a fixed dose, not a per-kg dose, so no structured paediatric per-kg entry is given here. Reduced doses are recommended for patients weighing less than 12.5 kg; see the SmPC of the 40 mg/mL granules for oral suspension. Only one paediatric patient below 6 months of age has been exposed in clinical trials, so patients below 6 months should be treated with caution, and testing for C. difficile colonisation or toxin is not recommended in children younger than 1 year because of the high rate of asymptomatic colonisation. Verify all paediatric dosing against a children's formulary.

Dose adjustments

Renal

eMC §4.2: no dose adjustment is considered necessary. Because of the limited clinical data in this population, fidaxomicin should be used with caution in patients with severe renal impairment.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Hypersensitivity to the active substance or to any of the excipients (eMC §4.3)
Not a contraindication but a §4.4 caution: hypersensitivity reactions including severe angioedema have been reported and some affected patients reported a history of allergy to macrolides, so fidaxomicin should be used with caution in patients with a known macrolide allergy; discontinue and take appropriate measures if a severe allergic reaction occurs

Side effects

Nausea (2.7%), vomiting (1.2%) and constipation (1.2%) - the most common adverse reactions
Rash and pruritus - common
Dizziness, headache and dysgeusia - common
Decreased appetite (common); abdominal distension, flatulence and dry mouth (uncommon)
Acute hypersensitivity reactions including angioedema and dyspnoea - reported post-marketing, frequency not known; discontinue fidaxomicin if a severe hypersensitivity reaction occurs. In paediatric patients (136 studied from birth to under 18 years) the frequency, type and severity of reactions are expected to be the same as in adults, with two additional cases of urticaria reported

Interactions

Potent P-glycoprotein inhibitors such as cyclosporine, ketoconazole, erythromycin, clarithromycin, verapamil, dronedarone and amiodarone - co-administration is NOT recommended (eMC §4.4 and §4.5); if given concomitantly, caution is advised. Single doses of cyclosporine A with fidaxomicin produced a 4-fold increase in fidaxomicin Cmax and a 2-fold increase in AUC, and a 9.5-fold and 4-fold increase respectively in Cmax and AUC of the main active metabolite OP-1118
P-glycoprotein substrates - fidaxomicin may be a mild to moderate inhibitor of intestinal P-gp. It had a small but not clinically relevant effect on digoxin exposure, but a larger effect on P-gp substrates with lower bioavailability that are more sensitive to intestinal P-gp inhibition, such as dabigatran etexilate, cannot be excluded (eMC §4.5)
DIVERGENCE TO RESOLVE: the US labelling §7.1 concludes the opposite of the UK SPC - it states that concomitant P-gp inhibitor use had no attributable effect on safety or treatment outcome in controlled trials and that fidaxomicin may be co-administered with P-gp inhibitors with no dose adjustment recommended

Clinical monograph

How it works

It inhibits bacterial RNA polymerase, giving a narrow spectrum targeted at C. difficile with minimal disruption of the normal gut flora.

Prescribing in practice

It is associated with lower rates of recurrence than vancomycin in C. difficile infection, which is its main clinical advantage and informs its place in therapy.
It acts locally in the gut with minimal systemic absorption, so systemic toxicity is limited.
Use should follow local infection-control and antimicrobial stewardship guidance for C. difficile.

Monitoring

Monitor resolution of diarrhoea and stool frequency, hydration, and for recurrence after treatment.

Counselling the patient

Complete the full course even if symptoms improve quickly.
Report any return of diarrhoea after finishing treatment.
Maintain good hand hygiene to limit spread of infection.

Evidence & guidelines

NICE recommends fidaxomicin for Clostridioides difficile infection, supported by trials showing reduced recurrence compared with vancomycin.

Reference: NICE NG199; UK CDI guidelines; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways