Fosfomycin tromethamine is a broad-spectrum bactericidal antibiotic indicated primarily for the treatment of uncomplicated urinary tract infections (UTIs) caused by susceptible strains of designated microorganisms. As a phosphonic acid derivative, it exerts its effect by inhibiting bacterial cell wall synthesis at an early stage, offering a unique mechanism that minimizes cross-resistance with other antibiotic classes. Its favorable pharmacokinetic profile, including high urinary concentration and rapid excretion, makes it a valuable therapeutic option in both community and hospital settings. This agent is particularly noted for its activity against multidrug-resistant pathogens, providing a critical tool in the era of increasing antimicrobial resistance.

Features

• Chemical structure: (1R,2S)-1,2-epoxypropylphosphonic acid as tromethamine salt
• Mechanism of action: Irreversible inhibition of UDP-N-acetylglucosamine enolpyruvyl transferase (MurA), preventing peptidoglycan precursor formation
• Spectrum: Broad Gram-positive and Gram-negative coverage including Escherichia coli, Enterococcus faecalis, and extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae
• Formulation: Single-dose sachet containing 3g fosfomycin tromethamine powder for oral solution
• Bioavailability: Approximately 34–58% in fasting state; significantly enhanced with food
• Elimination half-life: 4–8 hours with primarily renal excretion
• Pregnancy category: B (no evidence of risk in human studies)

Benefits

• Single-dose administration enhances patient compliance and reduces treatment abandonment
• Maintains efficacy against many multidrug-resistant uropathogens, including ESBL-producing E. coli
• Low potential for cross-resistance due to unique mechanism of action
• Favorable safety profile with minimal systemic side effects
• Suitable for use in pregnant patients when clearly indicated
• Rapid urinary bactericidal concentration achieved within 2–4 hours post-administration

Common use

Fosfomycin tromethamine is primarily indicated for the treatment of uncomplicated urinary tract infections (acute cystitis) in women caused by susceptible strains of Escherichia coli and Enterococcus faosaecalis. It may also be used off-label for complicated UTIs, asymptomatic bacteriuria in pregnancy, and surgical prophylaxis in urologic procedures. Clinical studies demonstrate efficacy rates of 70–90% for uncomplicated UTIs when caused by susceptible organisms. The drug is particularly valuable in regions with high prevalence of antibiotic-resistant uropathogens or for patients with penicillin allergies where other options are limited.

Dosage and direction

Adults and children ≥12 years: Single 3g dose orally mixed with water (approximately ½ glass). Administer immediately after preparation.

Administration instructions:

1. Empty entire contents of sachet into 90–120 mL (3–4 ounces) of cold water
2. Stir to dissolve completely (do not use hot water)
3. Administer on an empty stomach (2–3 hours before or after meals) for optimal absorption
4. For diabetic patients: contains 2.8g sucrose per dose

Renal impairment:

• CrCl 10–50 mL/min: No dosage adjustment necessary
• CrCl <10 mL/min: Not recommended

Hepatic impairment: No dosage adjustment required

Precautions

• Use with caution in patients with history of gastrointestinal diseases, particularly colitis
• Monitor for superinfection or fungal overgrowth during treatment
• Not recommended for treatment of pyelonephritis or perinephric abscess
• Contains sucrose; caution in patients with diabetes mellitus or glucose-galactose malabsorption
• May cause false-positive urinary glucose determinations with copper reduction tests
• Culture and susceptibility testing should be performed before treatment initiation when possible

Contraindications

• Hypersensitivity to fosfomycin or any component of the formulation
• Severe renal impairment (creatinine clearance <10 mL/min)
• Concomitant use with metoclopramide (may decrease fosfomycin serum concentrations)
• Children under 12 years of age (safety and efficacy not established)

Possible side effect

Common (≥1%):

• Diarrhea (9%)
• Nausea (5%)
• Headache (4%)
• Vaginitis (3%)
• Rhinitis (2%)

Less common (<1%):

• Dizziness, dyspepsia, abdominal pain
• Back pain, dysmenorrhea
• Rash, pruritus
• Asthenia, insomnia

Rare (<0.1%):

• Pseudomembranous colitis
• Anaphylactic reactions
• Hepatic enzyme elevations
• Eosinophilia

Drug interaction

• Metoclopramide: Decreases fosfomycin serum concentrations (contraindicated)
• Probenecid: May decrease urinary excretion of fosfomycin
• Antacids containing calcium or magnesium: May decrease fosfomycin absorption
• Oral contraceptives: Theoretical potential for reduced efficacy; recommend backup contraception
• Warfarin: Limited data; monitor INR periodically

Missed dose

As fosfomycin tromethamine is administered as a single dose, missed dose scenarios are not applicable. If vomiting occurs within 2–4 hours of administration, consider re-administration of the dose. Consult healthcare provider for guidance.

Overdose

No specific antidote exists. Cases of overdose are rare due to the drug’s safety profile. Symptoms may include gastrointestinal distress (nausea, vomiting, diarrhea). Management should include supportive care and maintenance of hydration. Hemodialysis may remove approximately 30–40% of the drug based on its molecular weight (259.2 g/mol) and low protein binding.

Storage

• Store at controlled room temperature (20–25°C/68–77°F)
• Protect from moisture
• Keep sachet in original packaging until use
• Reconstituted solution should be used immediately
• Keep out of reach of children

Disclaimer

This information is provided for educational purposes only and does not constitute medical advice. Prescribing decisions should be based on professional clinical judgment, susceptibility testing, and official prescribing information. Healthcare providers should consult full prescribing information and current clinical guidelines before administration. Not all possible uses, interactions, or adverse effects are included here.

Reviews

“Fosfomycin remains an essential tool in our antimicrobial arsenal, particularly for multidrug-resistant UTIs in outpatient settings. Its single-dose administration significantly improves adherence compared to traditional multi-day regimens.” – Infectious Disease Specialist, University Hospital

“Clinical efficacy data consistently shows fosfomycin maintains activity against ESBL-producing E. coli when other oral options are limited. Its safety profile makes it suitable for various patient populations.” – Clinical Pharmacologist, Research Institute

“While resistance monitoring is essential, fosfomycin’s unique mechanism continues to provide value in our increasingly complex antimicrobial landscape. Appropriate use is crucial to preserve its effectiveness.” – Medical Director, Antimicrobial Stewardship Program