Fosfomycin

Class: Phosphonic acid derivative antibiotic

Mechanism of Action: Inhibits bacterial cell wall synthesis by blocking the enzyme enolpyruvyl transferase, which is essential for peptidoglycan synthesis. Broad-spectrum activity against Gram-positive and Gram-negative bacteria, including E. coli and Enterococcus faecalis.

Indications

• Uncomplicated urinary tract infections (UTIs) in women
• Prophylaxis for recurrent UTIs
• Occasionally used for multidrug-resistant infections (off-label)

Dosage

• Adults: 3 g oral single dose (as fosfomycin tromethamine) for uncomplicated UTI
• Children: 50 mg/kg oral single dose (max 3 g) for uncomplicated UTI
• Multiple doses or IV formulation may be used in complicated infections (consult specialist)

Maximum Dose

3 g single oral dose (standard for uncomplicated UTI)

Major Side Effects

• Gastrointestinal: diarrhea, nausea, vomiting, abdominal pain
• Headache
• Dizziness
• Hypersensitivity reactions (rare)
• Urticaria or rash

Contraindications

• Hypersensitivity to fosfomycin
• Severe renal impairment (oral dose should be used cautiously)

Compatible Fluids

• Oral: dissolve in 90–120 mL of water before ingestion
• IV: compatible with 5% Dextrose and 0.9% Sodium Chloride

Route of Administration

• Oral (for uncomplicated UTI)
• Intravenous (IV) for severe or complicated infections

Type of Administration

• Oral: single dose, take on empty stomach or with water
• IV: slow infusion over 30–60 minutes

Special Precautions

• Use cautiously in renal impairment
• Monitor for allergic reactions
• Maintain adequate hydration to prevent crystalluria
• Resistance can develop; avoid repeated use unless indicated