Fidaxomicin

Fidaxomicin May be taken with or without food.

Granules for oral susp: Before reconstitution, shake the bottle to ensure the granules move and no caking has occurred. Reconstitute the granules for oral susp by adding 130 mL of purified water into the bottle. Hold the bottle in horizontal position, then shake vigorously for ≥2 minutes. Check if a homogeneous susp is obtained; if not, repeat shaking. Once a homogeneous susp is achieved, shake for another 30 seconds. Let it stand for 1 minute. Verify that the susp is still homogeneous; if not, repeat the shaking sequence. Instructions on reconstitution may vary among countries and between individual products. Refer to specific product guidelines.

Hypersensitivity to fidaxomicin.

Patient with fulminant or life-threatening C. difficile infections; known macrolide allergy. Not indicated for systemic infections due to minimal systemic absorption. Severe renal impairment and moderate to severe hepatic impairment. Children. Pregnancy and lactation.

Significant: Hypersensitivity reactions (e.g. dyspnoea, pruritus, rash, angioedema of mouth, face, throat).
Blood and lymphatic system disorders: Anaemia, neutropenia.
Gastrointestinal disorders: Vomiting, nausea, constipation, abdominal distention, flatulence, dry mouth, abdominal pain, gastrointestinal haemorrhage, dysgeusia, abdominal tenderness, dyspepsia, dysphagia, intestinal obstruction, megacolon.
General disorders and administration site conditions: Fever (particularly in children).
Investigations: Increased blood alkaline phosphatase, increased hepatic enzymes; decreased blood bicarbonate, decreased platelet count.
Metabolism and nutrition disorders: Decreased appetite, hyperglycaemia, metabolic acidosis.
Nervous system disorders: Dizziness, headache.

Perform culture and susceptibility tests; consult local institutional recommendations before treatment initiation due to antibiotic resistance risks. Monitor for signs and symptoms of hypersensitivity reactions.

May increase plasma concentration with P-gp inhibitors (e.g. ciclosporin).

Description:
Overview: Fidaxomicin is a narrow-spectrum macrocyclic antibiotic with potent bactericidal activity against C. difficile. It has minimal to no activity against gram-negative bacteria.
Mechanism of Action: Fidaxomicin acts locally in the gastrointestinal tract on C. difficile. It binds to the bacterial RNA polymerases prior to the formation of the open DNA-RNA polymerase complex required for initiation of transcription, thereby inhibiting RNA synthesis and resulting in cell death in susceptible bacteria.
Pharmacodynamics: In vitro studies suggest a low frequency of spontaneous resistance to fidaxomicin in C. difficile. Specific mutation (Val-ll43-Gly) in the β subunit of RNA polymerase was seen in C. difficile isolate and is associated with reduced susceptibility to fidaxomicin. There is no reported cross-resistance to other antibiotic classes.
Pharmacokinetics:
Absorption: Poorly absorbed from the gastrointestinal tract. Time to peak plasma concentration: 1-5 hours.
Distribution: Largely confined to the gastrointestinal tract.
Metabolism: Undergoes intestinal hydrolysis to form the main, less active metabolite (OP-1118).
Excretion: Via faeces (>92% as unchanged drug or metabolite); urine (<1% as metabolite). Elimination half-life: Approx 12 hours (fidaxomicin); approx 11 hours (OP-1118).

Source: National Center for Biotechnology Information. PubChem Compound Summary for CID 10034073, Fidaxomicin. https://pubchem.ncbi.nlm.nih.gov/compound/Fidaxomicin. Accessed Feb. 25, 2026.

Tab/Granules for oral susp: Store between 15-30°C. Reconstituted oral susp: Store between 2-8°C for up to 12 days. Storage recommendations may vary among countries and between individual products. Refer to specific product guidelines.

Macrolides

A07AA12 - fidaxomicin ; Belongs to the class of macrolides. Used in the treatment of intestinal infections.

Brayfield A, Cadart C (eds). Fidaxomicin. Martindale: The Complete Drug Reference [online]. London. Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 19/12/2025.

Dificid Tablet, Film Coated and Granule, for Suspension (Merck Sharp & Dohme LLC). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed. Accessed 19/12/2025.

Fidaxomicin 200 mg Film-coated Tablets (Tillotts Pharma UK Ltd). MHRA. https://products.mhra.gov.uk. Accessed 19/12/2025.

Fidaxomicin 40 mg/mL Granules for Oral Suspension (Tillotts Pharma UK Ltd). MHRA. https://products.mhra.gov.uk. Accessed 19/12/2025.

Fidaxomicin. Gold Standard Drug Database in ClinicalKey [online]. Elsevier Inc. https://www.clinicalkey.com. Accessed 23/01/2026.

Fidaxomicin. UpToDate Lexidrug, AHFS DI (Adult and Pediatric) Online. American Society of Health-System Pharmacists, Inc. Waltham, MA. UpToDate, Inc. https://online.lexi.com. Accessed 19/12/2025.

Fidaxomicin. UpToDate Lexidrug, Lexi-Drugs Multinational Online. Waltham, MA. UpToDate, Inc. https://online.lexi.com. Accessed 19/12/2025.

Joint Formulary Committee. Fidaxomicin. British National Formulary [online]. London. BMJ Group and Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 19/12/2025.

Paediatric Formulary Committee. Fidaxomicin. BNF for Children [online]. London. BMJ Group, Pharmaceutical Press, and RCPCH Publications. https://www.medicinescomplete.com. Accessed 19/12/2025.