For a healthy adult woman with uncomplicated acute cystitis, should I use the 3‑gram fosfomycin trometamol powder sachet instead of a tablet form?

Fosfomycin Powder Sachet Is the Only Recommended Formulation for Uncomplicated Acute Cystitis

Use the 3-gram fosfomycin trometamol powder sachet mixed with water—this is the only FDA-approved and guideline-endorsed formulation for treating uncomplicated acute cystitis in adult women. 1

Why the Powder Sachet Is Standard

• The FDA-approved dosage is one sachet of fosfomycin tromethamine granules for oral solution, which must be mixed with water before ingesting and should never be taken in dry form. 1

• All major guidelines—including the Infectious Diseases Society of America (IDSA), European Association of Urology (EAU), and American Urological Association (AUA)—recommend fosfomycin trometamol 3 g as a single oral dose, referring specifically to the powder sachet formulation. 2, 3

• The powder sachet achieves peak urinary concentrations of approximately 4000 µg/mL and maintains therapeutic levels above 100 µg/mL for 24–48 hours after a single 3-gram oral dose, which is the pharmacokinetic profile validated in clinical trials. 4

Clinical Efficacy of the Powder Formulation

• The single 3-gram powder sachet provides approximately 91% clinical cure rates in women with uncomplicated cystitis, with initial-infection resistance rates around 2.6%. 3

• Although fosfomycin's bacteriological eradication rates (78–83%) are modestly lower than nitrofurantoin (88%) or trimethoprim-sulfamethoxazole (94%), its overall clinical efficacy is comparable while offering single-dose convenience and minimal disruption to intestinal flora. 2, 3

• The powder formulation has been studied extensively in randomized controlled trials comparing it to 7-day nitrofurantoin courses, demonstrating non-inferior clinical and bacteriological cure rates with the advantage of single-dose administration. 5

Why Tablet Formulations Are Not Recommended

• No tablet formulation of fosfomycin is FDA-approved or mentioned in any major guideline for uncomplicated cystitis. 2, 3, 1

• The powder sachet is specifically designed to achieve the high urinary concentrations needed for single-dose efficacy; alternative formulations have not been validated in clinical trials or approved by regulatory authorities. 1, 4

• All published efficacy and safety data—including the low resistance rates and favorable adverse-effect profile—are based exclusively on the 3-gram powder sachet formulation. 3, 4, 6

Administration Instructions

• Mix the entire contents of one 3-gram sachet with 90–120 mL (3–4 ounces) of water and drink immediately after stirring. 1

• Fosfomycin may be taken with or without food, but should be administered after the patient has emptied her bladder to maximize urinary concentration. 1, 6

• The single-dose regimen improves adherence compared to 3–7 day courses of other antibiotics, which is a key advantage in outpatient management. 3

When to Avoid Fosfomycin (Regardless of Formulation)

• Do not use fosfomycin when early pyelonephritis is suspected (fever > 38°C, flank pain, costovertebral angle tenderness), as it lacks sufficient tissue penetration for upper urinary tract infections. 2, 3, 7

• Fosfomycin is not recommended for complicated UTIs, catheter-associated infections, or UTIs in men due to limited efficacy data in these populations. 3

Common Pitfall to Avoid

• Never prescribe a "tablet form" of fosfomycin for uncomplicated cystitis—only the FDA-approved powder sachet has demonstrated efficacy and safety in clinical trials and is endorsed by all major guidelines. 2, 3, 1