Fosfomycin
Related Subjects:
|Acute Pyelonephritis and Urosepsis (UTI)
|Urinary symptoms
|Antibiotic Guidelines
💊 Fosfomycin is a broad-spectrum bactericidal antibiotic. Orally it is a single 3 g dose for uncomplicated lower UTI in women, and it is often active against ESBL-producing *E. coli*. IV fosfomycin is a specialist (microbiology-advised) reserve agent.
📖 About
- A phosphonic acid derivative with no cross-resistance to other antibiotic classes.
- Oral: fosfomycin trometamol granules. IV: fosfomycin sodium (high sodium load).
- Always check the BNF for up-to-date prescribing advice.
⚙️ Mode of Action
- Irreversibly inhibits MurA (enolpyruvyl transferase) → blocks the first step of peptidoglycan synthesis → bactericidal.
- Active against *E. coli*, *Enterococcus faecalis*, *Staph. aureus* (including many MRSA) and many Enterobacterales.
🎯 Indications
- Acute uncomplicated lower UTI in non-pregnant women - a second-choice option in NICE NG109 (e.g. when nitrofurantoin or trimethoprim are unsuitable or resistance is likely).
- Prophylaxis for transrectal prostate biopsy.
- IV: complicated UTI, osteomyelitis, hospital-acquired pneumonia, bacterial meningitis and other serious infections when first-line agents are unsuitable - specialist advice only.
💊 Dose
| Indication | Dose | Route |
|---|
| Uncomplicated lower UTI (women) | 3 g as a single dose | Oral granules |
| Transrectal prostate biopsy prophylaxis | 3 g 3 hours before the procedure, then 3 g 24 hours after | Oral granules |
| Complicated UTI | 12–16 g daily in 2–3 divided doses (max 8 g per dose) | IV infusion |
| Other severe infections | 12–24 g daily in 2–3 divided doses (max 8 g per dose) | IV infusion |
🥤 How to Take the Oral Granules
- Dissolve in a glass of water and take on an empty stomach (2–3 hours before or after food), ideally at bedtime after emptying the bladder.
🫘 Renal Impairment
- Oral: avoid if eGFR <10 mL/min.
- IV: reduce the dose according to creatinine clearance (see BNF/SmPC).
🔄 Interactions
- Metoclopramide (and other prokinetics) reduces oral absorption - separate by 2–3 hours or avoid.
- Food delays and reduces oral absorption.
⚠️ Cautions
- IV sodium load: about 14 mmol sodium per 1 g → risk of hypernatraemia, fluid overload and hypokalaemia; caution in heart failure, hypertension, hyperaldosteronism and oedema. Monitor electrolytes.
- Elderly; hepatic impairment (IV).
- *C. difficile*-associated diarrhoea.
🚫 Contraindications
💥 Side Effects
- Oral: diarrhoea, nausea, dyspepsia, headache, dizziness, vulvovaginitis.
- IV: hypernatraemia, hypokalaemia, phlebitis, rash, raised transaminases, *C. difficile* colitis (rare), anaphylaxis (rare).
📚 References
