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Oral fosfomycin is an antibiotic used for selected acute, uncomplicated lower urinary tract infections. It blocks an early step in bacterial cell-wall production and reaches high concentrations in urine, which is why a single sachet can be enough for an eligible case. Fever, flank pain, pregnancy and recurrent infections can require a different assessment.

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What it is

Active ingredient: Fosfomycin · Form: Granules for oral solution · Dosages: 3 g sachet
A common regimen for eligible uncomplicated cystitis is one 3 g sachet dissolved in water and taken on an empty stomach. Symptoms should begin easing within days. The indication, regimen and follow-up depend on your history and country guidance — a licensed doctor decides whether it is appropriate, and prescribing is never automatic.

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How it works

Fosfomycin irreversibly inhibits MurA (UDP-N-acetylglucosamine enolpyruvyltransferase), the enzyme that catalyses the first committed step of peptidoglycan synthesis. It acts as a phosphoenolpyruvate (PEP) analogue, covalently binding to the cysteine 115 residue of MurA and blocking the formation of UDP-GlcNAc-enoylpyruvate. (Silver, Cold Spring Harb Perspect Med 2017, PMID 28062557) Fosfomycin reaches high concentrations in urine because it is cleared largely unchanged by the kidneys.

Short regimen when suitable

Uncomplicated cystitis in an eligible woman may be treated with one prescribed sachet.

Diagnosis checked first

The review looks for warning signs of kidney infection or a complicated UTI.

Antibiotic stewardship

It is prescribed only when symptoms, history and local guidance support it.

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How to use it

1

Dissolve one 3 g sachet in water

Empty the whole sachet into a glass of water, stir, and drink immediately. Do not swallow the granules dry and do not save part of the prepared solution.
2

Take on an empty stomach

Take it about 2–3 hours before or after food, preferably at bedtime after emptying the bladder. The usual regimen for acute uncomplicated cystitis in women and female adolescents is one single 3 g dose.

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Dose schedule

Take the sachet once at the agreed time. Do not repeat it the next day unless a clinician has issued a different indication. Symptoms should be reassessed if they are worsening or not beginning to improve within 2–3 days. Fever, flank pain, pregnancy, recurrent infection, or infection in men needs a different pathway.

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What has been reported

Diarrhoea, nausea, indigestion, headache and vaginal symptoms can occur. Thrush can also occur. Severe, persistent, or bloody diarrhoea can rarely indicate antibiotic-associated colitis and needs urgent advice — do not self-treat it with anti-diarrhoeal medicine.
Contact your doctor or seek urgent care for fever, chills, flank or back pain, vomiting, confusion, pregnancy, or feeling acutely unwell — these need prompt assessment. The same applies to a severe allergic reaction, or severe, persistent or bloody diarrhoea.

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Who it is not suitable for

Fosfomycin is not suitable if you have signs of kidney infection, sepsis or a complicated UTI, or if you have severe kidney impairment (creatinine clearance below 10 mL/min) or a previous serious reaction. In severe renal impairment, urinary concentrations are too low to be reliably bactericidal because fosfomycin is cleared almost entirely by glomerular filtration. Fosfomycin is used for selected susceptible lower urinary infections — one sachet does not suit every urinary symptom and does not treat a kidney infection. Fosfomycin enters bacteria through two active transport systems, GlpT and UhpT, which normally import glycerol-3-phosphate and glucose-6-phosphate respectively. (Silver, Cold Spring Harb Perspect Med 2017, PMID 28062557) This Trojan-horse uptake mechanism contributes to its selectivity: mammalian cells lack these transporters and are not affected.

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Storage

Keep in the original package, away from moisture and direct heat, and out of children’s reach. Follow the temperature limit on your pack and do not use it after the expiry date.

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How Hi-Doctor handles it

1

Before treatment

Review of symptoms and red flags.
2

Dose

Dissolve the prescribed sachet and take it promptly.
3

Follow-up

Seek review if symptoms persist or worsen.
An EU-licensed doctor reads your questionnaire and answers within 24 hours. If the doctor decides it is not safe to prescribe, the consultation fee is refunded in full. See pricing for the current consultation fee.

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Start a consultation

Sexual health consultation

Answer the sexual health questionnaire and a registered doctor reviews it. They decide whether treatment is appropriate, which one, and at what dose — and declining is a normal outcome. See what it costs and how the review works.
This page is reference information, not medical advice and not a prescription. Whether a medicine is appropriate for you is decided by a registered doctor after reviewing your consultation.