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Safety information · Internal patient-safety page

Fosfomycin safety summary

Fosfomycin is a single-dose antibiotic for uncomplicated bladder infections (cystitis). One sachet dissolved in water, ideally at bedtime, on an empty stomach, after emptying the bladder, and symptoms typically settle over the next 2–3 days.

Fosfomycin 3g

What it's used for

  • Dissolve the sachet in a glass of water and drink immediately.
  • Take on an empty stomach, 2–3 hours away from meals, because food reduces absorption.
  • Best taken at bedtime, after emptying the bladder, so the medicine sits in the bladder overnight.
  • A single dose is the complete treatment; symptoms improve over 2–3 days.

Most common side effects

  • Diarrhoea or loose stools.
  • Nausea.
  • Headache.
  • Dizziness.
  • Vaginal irritation or thrush.

Serious side effects: stop and seek care

  • Severe allergic reaction: rash, swelling of the face or throat, difficulty breathing.
  • Severe, persistent or bloody diarrhoea, even weeks later, can signal a C. difficile gut infection.

Who should not take it

  • Severely reduced kidney function.
  • Patients on haemodialysis.
  • Allergy to fosfomycin or any ingredient of the granules.

Interactions to flag

  • Metoclopramide and other medicines that speed up gut transit reduce fosfomycin absorption.
  • Food delays and reduces absorption: keep the 2–3 hour gap from meals.
  • Tell your doctor about everything you take, including over-the-counter products.

Message us in the app chat if you notice any of these

  • No improvement after 3 days, or symptoms getting worse.
  • Fever, chills or pain in your back or side: possible kidney infection, which needs different treatment.
  • Blood in your urine.
  • Rash, swelling or trouble breathing: call emergency services first.
AEMPS CIMA: Fosfomycin 3 g

This page summarises information from the regulator-approved leaflet for reference only. It is not medical advice and does not replace the assessment of an EU-licensed doctor. Your doctor will review your individual history, dose and interactions during your consultation.

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