Does fosfomycin (antibiotic) have a diuretic effect?

Fosfomycin Does Not Have Diuretic Effects

Fosfomycin is an antibiotic that works by inhibiting bacterial cell wall synthesis and has no diuretic properties. The confusion may arise from the fact that fosfomycin is excreted unchanged through the kidneys and achieves high urinary concentrations, but this is simply its route of elimination, not a diuretic effect 1, 2.

Mechanism and Pharmacology

• Fosfomycin irreversibly blocks bacterial cell wall synthesis by inhibiting phosphoenolpyruvate synthetase (MurA enzyme), which has no relationship to fluid balance or renal sodium/water handling 3, 2.

• The drug is not metabolized and is predominantly excreted unchanged in urine through glomerular filtration, achieving mean peak urinary concentrations of 1053-4415 mg/L within 4 hours of a single 3-gram oral dose 2.

• Fosfomycin does not bind to plasma proteins and achieves therapeutic urinary concentrations for 24-48 hours after a single dose, but this reflects renal clearance rather than any diuretic action 1, 2.

Important Clinical Caveat

• The intravenous formulation of fosfomycin disodium contains high sodium content and is actually contraindicated in patients with hypernatremia, cardiac insufficiency, and renal insufficiency 3. This sodium load could theoretically cause fluid retention rather than diuresis, making it particularly important to avoid in volume-overloaded states.

What May Cause Confusion

• Patients may experience increased urination frequency as a symptom of the urinary tract infection itself (urgency, frequency, nocturia), not from the antibiotic 4.

• The high urinary concentrations achieved by fosfomycin are due to renal excretion of the drug, not increased urine production 5, 6.