Prescription ·Strong evidence ·Reviewed May 2026
Fosfomycin is a broad-spectrum bactericidal antibiotic most commonly used as a single oral 3 g dose (as fosfomycin tromethamine) to treat uncomplicated urinary tract infections (acute cystitis) in women. It retains activity against many multidrug-resistant uropathogens, including extended-spectrum beta-lactamase (ESBL) producing Escherichia coli, because of its distinct mechanism and limited cross-resistance. Its convenient single-dose regimen supports adherence, though it is not appropriate for pyelonephritis or other complicated upper-tract or systemic infections in its oral form.
The bottom line
Evidence rating strong. Most-documented uses: treatment of uncomplicated urinary tract infections (acute cystitis) in women, effective single-dose option against many multidrug-resistant uropathogens including esbl-producing e. coli, convenient one-dose regimen that supports adherence. 3 sources indexed (2008–2017), with 6 interaction records on file.
Core mechanism
Fosfomycin is a phosphoenolpyruvate analog that irreversibly inhibits MurA (UDP-N-acetylglucosamine enolpyruvyl transferase), the enzyme catalyzing the first committed step of bacterial peptidoglycan (cell wall) biosynthesis. By covalently binding a cysteine residue in the MurA active site, it blocks the conversion of UDP-N-acetylglucosamine to UDP-N-acetylglucosamine enolpyruvate, halting murein assembly and producing bactericidal cell lysis. The drug enters bacterial cells via the glycerophosphate (GlpT) and hexose phosphate (UhpT) transport systems, and it concentrates in the urine, where high levels support its efficacy in lower urinary tract infections.2,1
Oral bioavailability of fosfomycin tromethamine is roughly 30-40 percent and is reduced by food, so it is best taken on an empty stomach (about 2-3 hours before or after a meal). Dissolve the granules in cool water, not hot, and drink immediately. It is renally excreted largely unchanged, concentrating in the urine.1,3
Fosfomycin can suppress or kill bacterial probiotic organisms if taken at the same time, although selected probiotics may lower antibiotic-associated diarrhea risk.
Recommendation: Separate probiotic doses from the antibiotic by at least 2 hours when feasible; avoid probiotic use in severely immunocompromised patients or patients with central lines unless clinician-directed.
Psyllium can delay or reduce absorption of some oral drugs if taken at the same time as Fosfomycin.
Recommendation: Separate psyllium from Fosfomycin by at least 2 hours unless the prescriber gives different timing instructions.
Oral fosfomycin tromethamine is a single-dose therapy whose efficacy depends on achieving adequate urinary concentrations. Calcium is a divalent cation that can bind fosfomycin in the gut and reduce its oral absorption, lowering the urinary levels needed to clear an uncomplicated urinary tract infection.
Recommendation: Take the single fosfomycin dose on its own and avoid calcium supplements (or calcium-rich antacids and large dairy doses) for several hours around it. Because fosfomycin is usually a one-time dose, simply skip the calcium supplement on the day of treatment or separate it from the antibiotic.
Magnesium is a divalent cation that can chelate fosfomycin within the gut, similar to the documented interaction with magnesium-containing antacids. This may reduce fosfomycin absorption and the urinary drug levels required for a successful single-dose UTI treatment.
Recommendation: Avoid taking magnesium supplements (and magnesium-containing antacids) close to the single fosfomycin dose. Skipping or separating the magnesium dose on treatment day is the simplest approach.
Oral iron salts are polyvalent cations known to chelate many antibiotics in the gut. Iron can plausibly bind fosfomycin and reduce its absorption, potentially lowering the urinary antibiotic concentration needed for the single-dose treatment of an uncomplicated UTI.
Recommendation: Separate oral iron supplements from the single fosfomycin dose. Since fosfomycin is taken once, take the antibiotic alone and resume iron the following day or several hours apart.
Zinc is a divalent cation that, like other metal cations, can chelate fosfomycin in the gut and reduce its absorption. This may lower the urinary antibiotic concentration required to clear an uncomplicated urinary tract infection with a single dose.
Recommendation: Avoid taking zinc supplements at the same time as the single fosfomycin dose. Take the antibiotic separately and resume zinc a few hours later or the next day.
Numbered references. Citations throughout the page link here.
IDSA/ESCMID guidelines list fosfomycin trometamol 3 g single dose as an appropriate first-line agent for acute uncomplicated cystitis owing to minimal resistance and low collateral damage.
Fosfomycin acts as a phosphoenolpyruvate analog that irreversibly inhibits MurA (enolpyruvyl transferase), blocking the initial step of bacterial cell wall biosynthesis and conferring activity with limited cross-resistance.
Fosfomycin tromethamine 3 g as a single oral dose is approved for treatment of uncomplicated urinary tract infections (acute cystitis) caused by susceptible strains of E. coli and Enterococcus faecalis in women.
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