What is the appropriate dosing for Fosfomycin (phosphonic acid antibiotic)?

From the Guidelines

Fosfomycin should be dosed as a single 3-gram oral sachet for uncomplicated urinary tract infections in women, as recommended by the American College of Physicians 1. This dosing regimen is supported by the latest guidelines, which prioritize short-course antibiotics for uncomplicated cystitis and pyelonephritis.

• The American College of Physicians recommends fosfomycin as a single dose for women with uncomplicated bacterial cystitis 1.
• The Infectious Diseases Society of America and the European Society for Microbiology and Infectious Diseases also recommend fosfomycin as a single 3-gram dose for uncomplicated urinary tract infections 1.
• Additionally, a 2022 study published in the Journal of Microbiology, Immunology and Infection recommends a single dose of fosfomycin 3g PO for uncomplicated urinary tract infections due to multidrug-resistant organisms 1. The single-dose regimen is convenient and effective, with fosfomycin achieving high urinary concentrations within 2-4 hours after administration and maintaining therapeutic levels for 24-48 hours.
• Common side effects of fosfomycin include diarrhea, headache, nausea, and abdominal pain, but it is generally well-tolerated and has minimal drug interactions, making it suitable for patients on multiple medications.
• It is essential to take fosfomycin on an empty stomach, mixed with water, and consumed immediately after dissolution, and patients should be advised to empty their bladder before taking the medication.

From the FDA Drug Label

The recommended dosage for women 18 years of age and older for uncomplicated urinary tract infection (acute cystitis) is one sachet of fosfomycin tromethamine granules for oral solution. The recommended dosage of fosfomycin for uncomplicated urinary tract infection (acute cystitis) in women 18 years of age and older is one sachet of fosfomycin tromethamine granules for oral solution 2.

• The medication should be taken with water, as it should not be taken in its dry form.
• It may be taken with or without food.

From the Research

Fosfomycin Dosing

• Fosfomycin tromethamine is an oral antimicrobial indicated for the treatment of uncomplicated lower urinary tract infections (UTIs) 3
• A single dose of fosfomycin tromethamine 3.0 g is as clinically effective as 7- to 10-day treatment regimens of standard agents used to treat UTIs, such as nitrofurantoin, norfloxacin, and trimethoprim/sulfamethoxazole 3
• Single-dose oral fosfomycin (300 mg) has been found to be effective in the treatment of uncomplicated lower urinary tract infection (UTI) in women 4
• Fosfomycin-trometamol is recommended as a first-line treatment for uncomplicated cystitis (UC) 5
• Single-dose antimicrobial therapy, including fosfomycin trometamol, is now the treatment of choice for uncomplicated urinary tract infections in general practice 6
• A randomized clinical trial compared the clinical and microbiologic efficacy of nitrofurantoin and fosfomycin in women with uncomplicated cystitis, and found that 5-day nitrofurantoin resulted in a significantly greater likelihood of clinical and microbiologic resolution at 28 days after therapy completion compared to single-dose fosfomycin 7

Comparison with Other Treatments

• Fosfomycin tromethamine is as effective and safe as multidose comparators, such as nitrofurantoin, norfloxacin, and trimethoprim/sulfamethoxazole 3
• Single-dose fosfomycin presents a potentially useful and safe treatment option for the treatment of uncomplicated UTI in women and asymptomatic bacteriuria in pregnancy, with no significant differences in clinical and microbiological cure rates compared to nitrofurantoin 4
• Fosfomycin-trometamol, nitrofurantoin, or pivmecillinam are recommended as first-line treatments for uncomplicated cystitis (UC) 5
• Trimethoprim or co-trimoxazole are currently the preferred agents for single-dose therapy, but fosfomycin trometamol and the 4-quinolones are promising agents 6

Safety and Efficacy

• Fosfomycin tromethamine is well tolerated and appears safe to use during pregnancy 3
• The incidence of adverse events was found to be more in fosfomycin relative to the nitrofurantoin group, but adverse events were few and primarily gastrointestinal 4, 7
• Fosfomycin tromethamine is active in the urine against common uropathogens that are associated with cystitis in women, including organisms resistant to other antibiotics 3