What is the recommended dose of fosfomycin (tromethamine) for treating uncomplicated urinary tract infections (UTIs)?

Fosfomycin Dosing for Uncomplicated UTI

The recommended dose of fosfomycin tromethamine for uncomplicated urinary tract infections is a single 3-gram oral dose, taken once. 1

Standard Dosing Regimen

• A single oral dose of fosfomycin tromethamine 3 grams is the FDA-approved and guideline-recommended treatment for acute uncomplicated cystitis in women. 2, 3, 4, 1
• The medication should be mixed with water before ingestion and may be taken with or without food. 1
• This single dose provides therapeutic urinary concentrations for 24-48 hours, which is sufficient to eradicate most uropathogens. 3, 5

Patient Population and Indications

• Fosfomycin is specifically indicated for uncomplicated cystitis in premenopausal, nonpregnant women with no urological abnormalities. 2
• The single 3-gram dose is also appropriate for pregnant women with asymptomatic bacteriuria or uncomplicated lower UTI. 3, 6
• Do not use fosfomycin for pyelonephritis, complicated UTIs, or routinely in men due to insufficient efficacy data for these populations. 3

Clinical Efficacy Considerations

• While fosfomycin demonstrates slightly inferior bacteriological efficacy compared to 3-day trimethoprim-sulfamethoxazole or nitrofurantoin regimens based on FDA submission data, its clinical efficacy is comparable. 2, 4
• The single-dose regimen offers significant advantages in patient adherence and convenience compared to multi-day courses. 3, 4
• Fosfomycin maintains minimal collateral damage to intestinal flora and has low resistance rates (only 2.6% in initial E. coli infections). 3, 4

When to Choose Fosfomycin

• Consider fosfomycin as first-line therapy when trimethoprim-sulfamethoxazole resistance exceeds 20% in your community. 2, 3
• Fosfomycin is particularly valuable for multidrug-resistant organisms including ESBL-producing E. coli, vancomycin-resistant Enterococcus (VRE), and MRSA causing uncomplicated cystitis. 3
• The single-dose convenience makes it especially useful in elderly populations where compliance with multi-day regimens may be challenging. 4

Important Contraindications and Cautions

• Use fosfomycin with caution in patients with hypernatremia, cardiac insufficiency, or renal insufficiency, as the elimination half-life increases dramatically from 5.7 hours to 40-50 hours in anuric patients. 3
• Common adverse effects include diarrhea, nausea, and vomiting, occurring in approximately 4.3% of patients. 3, 7

Follow-Up Recommendations

• Routine post-treatment urinalysis or urine cultures are not indicated for asymptomatic patients. 3
• If symptoms do not resolve by the end of treatment or recur within 2 weeks, perform urine culture and antimicrobial susceptibility testing. 3