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Phosphonic Acid Antibiotic Pregnancy: Use with caution — limited safety data; not first choice in pregnancy

Fosfomycin

Brand names: Monuril

Adult dose

Dose: 3 g single oral dose (sachet dissolved in water)
Route: Oral
Frequency: Single dose
Max: 3 g per course
NICE NG109: Third-line option for uncomplicated lower UTI in women. Single dose achieves high urinary concentrations for 24-48 hours. Take on empty stomach

Paediatric dose

Dose: Seek specialist opinion N/A/kg
Route: Oral
Frequency: Seek specialist opinion
Max: Seek specialist opinion
Seek specialist opinion

Dose adjustments

Renal

Avoid if eGFR under 10; no adjustment for eGFR above 10

Hepatic

No adjustment required

Paediatric weight-based calculator

Seek specialist opinion

Clinical pearls

  • Single-dose convenience is a major adherence advantage — particularly useful in patients who struggle with multi-day antibiotic courses
  • Active against E. coli and Enterococcus faecalis — useful in ESBL-producing E. coli UTIs (many retain fosfomycin sensitivity) — preserve for resistant organisms per antibiotic stewardship
  • NICE NG109: Third-line (after nitrofurantoin and trimethoprim) for uncomplicated lower UTI — first-line for ESBL-producing organisms or where first-line agents contraindicated
  • Oral fosfomycin achieves high urinary concentrations but poor systemic levels — not suitable for upper UTI, complicated UTI, or bacteraemia
  • Not the same as IV fosfomycin used for serious systemic infections — oral formulation is purely for lower urinary tract

Contraindications

  • Severe renal impairment (eGFR under 10)

Side effects

  • Diarrhoea (most common)
  • Nausea
  • Headache
  • Vulvovaginal candidiasis

Interactions

  • Metoclopramide (reduces fosfomycin absorption — avoid combination)

Monitoring

  • Symptom resolution within 48-72 hours
  • Urine culture if no improvement

Reference: BNFc; BNF 90; NICE NG109 (UTI in adults); PHE Antimicrobial Prescribing Guidelines; EUCAST resistance data. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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