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Pharmacology · Urinary antiseptics

Fosfomycin !

A small antibiotic that blocks the first step of cell-wall building. One oral sachet treats uncomplicated cystitis; an IV form is a WHO reserve drug.

Updated 2026-11-01

  • Class: Urinary antiseptics
  • Enzyme: UDP-N-acetylglucosamine enolpyruvyl transferase (MurA)
  • ATC code: J01XX01
  • WHO Model List of Essential Medicines

The figure shows Escherichia coli MurA with fosfomycin bonded covalently to its active site (the ligand is the opened fosfomycin adduct).

Target in 3D: UDP-N-acetylglucosamine enolpyruvyl transferase (MurA). PDB structure 1UAE (RCSB PDB, public domain). View the structure at RCSB PDB

Mechanism of action

Fosfomycin mimics phosphoenolpyruvate and binds MurA, the enzyme that starts peptidoglycan synthesis by joining phosphoenolpyruvate to UDP-N-acetylglucosamine. It forms a covalent bond in the active site, so the enzyme is permanently blocked and the bacterium cannot build its wall. It is bactericidal.

  1. Enters the bacterium through sugar-phosphate transporters
  2. Mimics phosphoenolpyruvate at MurA
  3. Bonds covalently and blocks the enzyme
  4. Cell-wall synthesis stops and the bacterium dies

Pharmacokinetics

Absorption
Oral granules of fosfomycin tromethamine, dissolved in water.
Distribution
High urinary levels for a long time after a single dose.
Elimination
Unchanged in the urine and faeces.
Half-life
About 5.7 hours after an oral dose.

Indications

Adverse effects

Common

  • Diarrhoea
  • Headache and nausea
  • Vaginal infection

Contraindications

  • Known allergy to fosfomycin
  • Oral form not used for pyelonephritis

Key interactions

Metoclopramide
Lowers fosfomycin levels in blood and urine.

What is monitored

  • Symptoms after treatment; urine culture if they persist
  • Stool pattern

Administration and safety

  • The sachet is always dissolved in water before drinking, never swallowed dry
  • Usually given as a single dose

Nursing care

  • Explain that symptoms may take a few days to settle
  • Teach to report fever, flank pain or blood in the urine
  • Ask about allergies

Pregnancy and breastfeeding

Crosses the placenta; animal studies showed no birth defects.

Test yourself

Think of the answer, then tap the question to see it.

Which enzyme does fosfomycin block?

MurA, the enolpyruvyl transferase that starts peptidoglycan synthesis.

How is oral fosfomycin taken?

Granules dissolved in water, usually as a single dose.

Which drug lowers fosfomycin levels?

Metoclopramide.

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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: DailyMed - FOSFOMYCIN TROMETHAMINE granule, for solution (DailyMed (U.S. National Library of Medicine), 2026); Fosfomycin: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); eEML - Electronic Essential Medicines List (World Health Organization, 2025); STRUCTURE OF UDP-N-ACETYLGLUCOSAMINE ENOLPYRUVYL TRANSFERASE (RCSB Protein Data Bank, 2026).

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Representative model, for educational purposes only.