An antibiotic for urine infections
Fosfomycin
An antibiotic, usually taken as a single oral sachet, for uncomplicated urinary tract infections.
What is Fosfomycin?
Fosfomycin is an antibiotic used mainly for uncomplicated urinary tract infections, usually taken as a single sachet dissolved in water. It is helpful when an infection is caused by bacteria that resist other antibiotics. It is taken on an empty stomach, ideally at bedtime after emptying the bladder, so it stays in the urine for as long as possible.
Education and reference only. This is a plain-language guide to Fosfomycin — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Fosfomycin is an antibiotic used mainly to treat uncomplicated urinary tract infections (UTIs), particularly cystitis in women. In the UK it is most often given as a single oral sachet dissolved in water. It is useful when an infection is caused by bacteria that are resistant to more common UTI antibiotics, as it concentrates well in the urine.
How it works
Fosfomycin blocks one of the very first steps bacteria use to build their cell wall. With this step disabled, the bacteria cannot make a proper wall and are killed. Because it is removed from the body into the urine, high levels build up in the bladder, which is why it works well for urine infections.
Company & origin
Originated / developed by: Available from several manufacturers; the oral sachet brand Monuril is supplied in the UK..
Derived from a soil micro-organism and first described in the early 1970s; the oral sachet is widely used as a single-dose treatment for urine infections.
Practical use
How to take Fosfomycin
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Empty your bladder, then dissolve the sachet in a glass of cold water and drink it straight away.
- Take it on an empty stomach, ideally at bedtime, so it stays in the urine overnight.
- Avoid eating for a couple of hours before and after, as food can reduce how well it is absorbed.
- Do not take it at the same time as antacids or certain mineral supplements, which can reduce its effect.
- A single sachet is often the whole treatment, so do not take more unless advised.
- Contact your prescriber if symptoms do not settle within a few days or come back.
Weighing it up
Advantages & disadvantages of Fosfomycin
Advantages
- Often a single, convenient sachet treatment, which makes it easy to complete.
- Useful against some bacteria that resist other common urine antibiotics.
- Concentrates strongly in the urine, where the infection is.
Disadvantages
- Mainly suited to simple bladder infections, not deeper or kidney infections.
- Must be taken on an empty stomach and away from food and certain supplements.
- Can cause diarrhoea and other gut upset.
Practical use
Good to know
The oral sachet is stirred into a glass of cold water and drunk straight away, on an empty stomach. It is best taken at bedtime after you have emptied your bladder, so the antibiotic stays in the urine overnight. A single sachet is often enough, although your prescriber may occasionally advise a further dose. Tell your prescriber if your symptoms do not improve within a few days.
Who should not take it / use with caution
- People who have had a serious allergic reaction to fosfomycin.
- People with a more complicated or kidney infection usually need a different antibiotic and course.
- People with significant kidney problems may not be suitable, as it relies on the kidneys to reach the urine.
Monitoring
- Usually none for a simple, single-dose treatment in an otherwise healthy person.
- Review if symptoms do not improve, suggesting a different treatment is needed.
- A urine test may be checked if the infection is recurrent or unclear.
Side effects
- Diarrhoea.
- Feeling sick or stomach upset.
- Headache.
- Dizziness.
- Thrush of the vagina.
Key interactions
- Metoclopramide and similar medicines that speed up the gut, which can lower fosfomycin levels.
- Antacids and certain mineral supplements, which can reduce how much is absorbed if taken together.
- Live typhoid vaccine, which may be less effective during antibiotic treatment.
Available as: Oral sachet (granules dissolved in water).
Answers
Fosfomycin: frequently asked questions
How do I take the fosfomycin sachet?
Empty your bladder first, then stir the sachet into a glass of cold water and drink it straight away on an empty stomach, ideally at bedtime so it stays in the urine overnight.
Is one sachet really enough?
For a simple bladder infection a single sachet is often the whole course, because it concentrates strongly in the urine. Your prescriber will tell you if you need a further dose.
Can I eat before taking it?
It is best taken on an empty stomach, avoiding food for a couple of hours before and after, because food can reduce how well it is absorbed.
What if my symptoms do not improve?
Contact your prescriber if your symptoms do not start to settle within a few days or come back, as you may need a different antibiotic or further checks.
Is fosfomycin suitable for a kidney infection?
The oral sachet is mainly for simple bladder infections. Deeper or kidney infections usually need a different antibiotic and a longer course.
The wider class
About UTI antibiotics
Fosfomycin belongs to the uti antibiotics class. For how the class as a whole works, its shared safety principles and monitoring, see the full guide.
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Authoritative sources
- BNF
- NICE CKS
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