Fosfomycin: Targeted Antibiotic for Uncomplicated Urinary Tract Infections
Fosfomycin
| Product dosage: 3g | |||
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Synonyms | |||
Fosfomycin tromethamine is a broad-spectrum bactericidal antibiotic indicated for the treatment of uncomplicated urinary tract infections (UTIs) caused by susceptible strains of designated microorganisms. As a phosphonic acid derivative, it exhibits a unique mechanism of action, inhibiting bacterial cell wall synthesis at an earlier stage than beta-lactams or glycopeptides. Its favorable pharmacokinetic profile, including high urinary concentrations and minimal systemic absorption, makes it a valuable therapeutic option in outpatient and empiric settings. This agent is particularly noted for its activity against multidrug-resistant pathogens, offering a reliable alternative when resistance patterns limit first-line treatments.
Features
- Chemical class: Epoxy phosphonic acid derivative; prodrug formulation as fosfomycin tromethamine
- Mechanism: Irreversible inhibition of UDP-N-acetylglucosamine enolpyruvyl transferase (MurA), preventing peptidoglycan precursor synthesis
- Spectrum: Broad bactericidal activity against Gram-positive and Gram-negative uropathogens, including Escherichia coli, Enterococcus faecalis, and Klebsiella pneumoniae
- Pharmacokinetics: Rapid absorption with peak serum concentrations within 2–4 hours; primarily excreted unchanged in urine (up to 95% renal clearance)
- Formulation: Single-dose sachet containing 3g fosfomycin tromethamine oral powder for reconstitution
- Stability: Reconstituted suspension remains stable for 24 hours at room temperature
Benefits
- Single-Dose Convenience: Complete therapeutic course administered as one oral dose, enhancing adherence and reducing premature discontinuation
- Low Resistance Development: Unique mechanism minimizes cross-resistance with other antibiotic classes, preserving long-term efficacy
- High Urinary Concentrations: Achieves bactericidal levels in urine for 36–48 hours post-dose, ensuring sustained antimicrobial action
- Favorable Safety Profile: Minimal systemic absorption reduces risk of systemic adverse effects and drug-drug interactions
- Activity Against MDR Pathogens: Effective against ESBL-producing Enterobacteriaceae and vancomycin-resistant enterococci in specific clinical scenarios
- Pregnancy Category B: May be used during pregnancy when clinically indicated, following risk-benefit assessment
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 faecalis. It may be used as empiric therapy in communities with high resistance rates to first-line agents like trimethoprim-sulfamethoxazole or fluoroquinolones. Off-label applications include prophylaxis for recurrent UTIs, treatment of complicated UTIs when susceptibility is confirmed, and management of asymptomatic bacteriuria in pregnancy. Clinical use should always be guided by local antibiograms and susceptibility testing when available.
Dosage and direction
Standard Adult Dose: 3g single dose orally mixed with ½ glass (4 oz) of cold water. Do not use hot water.
Administration: Dissolve entire contents of one sachet in water, stir to complete dissolution, and administer immediately. Best taken on an empty stomach (at least 2 hours before or after meals) to optimize absorption.
Renal Impairment: Caution advised in severe renal impairment (CrCl <10 mL/min); consider alternative therapy.
Pediatric Use: Safety and effectiveness in children under 12 years not established.
Geriatric Use: No dosage adjustment necessary unless severe renal impairment exists.
Precautions
- Use with caution in patients with history of gastrointestinal diseases, particularly colitis
- Monitor for superinfection or fungal overgrowth with prolonged use
- Not recommended for treatment of pyelonephritis or perinephric abscesses due to inadequate tissue penetration
- May cause false-positive urinary glucose determinations with copper reduction tests (e.g., Benedict’s solution)
- Consider susceptibility testing in recurrent infections or treatment failures
- Avoid concurrent administration with metoclopramide, which may decrease serum concentrations
Contraindications
- Known hypersensitivity to fosfomycin or any component of the formulation
- Patients with severe renal impairment (creatinine clearance <10 mL/min) due to inadequate urinary excretion
- Concomitant use with drugs that significantly decrease gastrointestinal motility
- Not indicated for treatment of systemic infections due to limited tissue penetration
Possible side effect
Common (≥1%):
- Diarrhea (8.5%)
- Nausea (5.2%)
- Headache (4.8%)
- Vaginitis (3.8%)
- Dizziness (1.5%)
Less common (<1%):
- Dyspepsia, abdominal pain
- Rash, pruritus
- Rhinitis, pharyngitis
- Back pain, dysmenorrhea
- Transient elevation of liver enzymes
Rare:
- Pseudomembranous colitis
- Anaphylactic reactions
- Hematologic abnormalities (eosinophilia, thrombocytopenia)
- Steven-Johnson syndrome (case reports)
Drug interaction
- Metoclopramide: Decreases fosfomycin serum concentrations; avoid concomitant use
- Cimetidine: May increase fosfomycin bioavailability; clinical significance unknown
- Oral contraceptives: No significant interaction demonstrated
- Warfarin: No clinically significant interaction reported
- Probenecid: May decrease renal excretion of fosfomycin; avoid combination
- Antacids: Aluminum and magnesium-containing antacids may decrease absorption; separate administration by 2 hours
Missed dose
As fosfomycin is administered as a single dose, missed dose protocols do not apply. If the patient fails to take the medication as directed, consult healthcare provider for assessment of whether re-administration is appropriate. Do not double dose.
Overdose
No specific antidote exists. Cases of overdose are rare due to limited systemic absorption. Expected manifestations would include exaggerated adverse effects, particularly gastrointestinal disturbances. Management should be supportive: gastric lavage if administered recently, maintenance of hydration, and symptomatic treatment. Hemodialysis may remove fosfomycin but is rarely indicated given its safety profile.
Storage
Store at controlled room temperature (20°–25°C or 68°–77°F). Keep sachet in original package until use. Protect from moisture. After reconstitution, store suspension at room temperature and discard any unused portion after 24 hours. Do not freeze. Keep out of reach of children.
Disclaimer
This information is for educational purposes only and does not constitute medical advice. Prescribing decisions must be made by qualified healthcare professionals based on individual patient characteristics, susceptibility testing, and clinical context. Local resistance patterns should guide empiric therapy selection. Always consult complete prescribing information before administration.
Reviews
“Fosfomycin remains a valuable option in our antimicrobial arsenal, particularly for multidrug-resistant UTIs. The single-dose regimen significantly improves adherence compared to traditional 3–7 day courses.” – Infectious Disease Specialist, University Hospital
“While resistance rates remain relatively low, we’ve observed some increase in MICs among ESBL-producing E. coli in recent years. Still an excellent choice for uncomplicated cystitis when local susceptibility supports its use.” – Clinical Microbiologist, Regional Laboratory
“Patient satisfaction scores are notably higher with fosfomycin compared to longer-course antibiotics. The convenience of single-dose therapy cannot be overstated in working populations.” – Urology Nurse Practitioner, Outpatient Clinic