Fosfomycin Preparation: Water Volume for Mixing
Mix the entire contents of one 3-gram fosfomycin sachet with 3 to 4 ounces (approximately 90–120 mL) of water, stir to dissolve, and drink immediately. 1
Detailed Preparation Instructions
Pour the complete sachet contents into ½ cup (3–4 ounces or ~90–120 mL) of water and stir until the granules fully dissolve. 1
Do not use hot water—room-temperature or cool water is required to preserve drug stability. 1
Drink the solution immediately after mixing; do not prepare in advance or allow the dissolved medication to sit. 1
Clinical Context and Efficacy
Fosfomycin 3 g as a single oral dose achieves therapeutic urinary concentrations of approximately 4,000 µg/mL, which remain above 100 µg/mL for 24–48 hours—sufficient to eradicate most uropathogens causing uncomplicated cystitis. 2, 3
Clinical cure rates of approximately 88.9–91 % and microbiological eradication rates of 78–94.9 % have been demonstrated in women with acute uncomplicated cystitis. 2, 4
Single-dose convenience improves adherence compared with 3–7 day regimens and minimizes disruption to intestinal flora. 2
Indications and Contraindications
Fosfomycin is recommended only for uncomplicated cystitis in women; it should not be used for pyelonephritis, complicated UTIs, or upper-tract infections due to insufficient tissue penetration. 2
Do not use fosfomycin if fever >38 °C, flank pain, or costovertebral-angle tenderness is present, as these signs indicate upper-tract involvement requiring a fluoroquinolone or parenteral cephalosporin. 2
No dosage adjustment is required in elderly patients, pregnant women, or those with renal or hepatic impairment. 3
Common Pitfalls to Avoid
Do not mix with hot water, as heat may degrade the active ingredient. 1
Do not prepare the solution in advance—efficacy depends on immediate consumption after mixing. 1
Do not prescribe fosfomycin for suspected pyelonephritis; switch to nitrofurantoin (5 days), trimethoprim-sulfamethoxazole (3 days if local resistance <20 %), or a fluoroquinolone (3 days) for treatment failures or recurrence within 2 weeks. 2