Phosphonic acid derivative (urinary tract)
Fosfomycin is an antibiotic used to treat uncomplicated urinary tract infections (acute cystitis) in women, given as a single oral dose of granules. It works by preventing bacteria from building their cell wall.
Also known as: Monuril
Antacids and calcium-containing preparations significantly reduce Fosfomycin absorption, compromising its efficacy in urinary tract infection.
Fosfomycin trometamol, used as a single dose in uncomplicated urinary tract infections, has reduced oral absorption when taken with food; co-administration with antacids or other drugs that change gastric pH or motility can further reduce its bioavailability and compromise efficacy. The label recommends taking the drug on an empty stomach and the Portuguese Prontuário Terapêutico advises separating from antacids. In practice, instruct the patient to take fosfomycin alone, on an empty stomach, and to space any antacid by 2–3 hours.
Antacids + fosfomycin: take fosfomycin on an empty stomach and separate from antacids to avoid reducing its absorption.
Antacids, calcium salts (and also metoclopramide) interfere with oral fosfomycin bioavailability, reducing the concentrations reached in the urinary tract.
Monitor the clinical response and resolution of urinary symptoms.
Persistent urinary tract infection symptoms after concurrent dosing.
Separate fosfomycin dosing from antacids and calcium supplements by several hours and avoid taking it with meals.
DailyMed/FDA (NIH/NLM) — approved Fosfomycin trometamol label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=4f206750-8126-99a3-e063-6294a90ade4c ; approved Antacids label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=c72f0736-ee20-45b4-baf0-b80f1e3fa9cb — with additional reference: Prontuário Terapêutico do INFARMED, INFARMED (11th ed., 2012)
Fosfomycin trometamol absorption is reduced when taken with food; taking on an empty stomach is recommended.
Take on an empty stomach, preferably at bedtime, after emptying the bladder.
DailyMed/FDA (NIH/NLM) — approved Fosfomycin trometamol label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=4f206750-8126-99a3-e063-6294a90ade4c
No relevant pharmacokinetic interaction; usual moderation during treatment.
Moderate alcohol intake.
DailyMed/FDA (NIH/NLM) — approved Fosfomycin trometamol label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=4f206750-8126-99a3-e063-6294a90ade4c
Fosfomycin is eliminated renally; renal impairment may require dose or interval adjustment.
Adjust based on renal function (single dose usually unadjusted, but reassess in severe RI).
DailyMed/FDA (NIH/NLM) — approved Fosfomycin trometamol label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=4f206750-8126-99a3-e063-6294a90ade4c
Fosfomycin trometamol contains a relevant amount of sodium, which can worsen hypertension and heart failure.
Consider the sodium content in patients with uncontrolled hypertension or heart failure.
DailyMed/FDA (NIH/NLM) — approved Fosfomycin trometamol label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=4f206750-8126-99a3-e063-6294a90ade4c
Data on fosfomycin in pregnancy are limited; use only if the benefit outweighs the risk (e.g., uncomplicated UTI).
Use only when indicated and with no safe alternative.
Present in breast milk in small amounts; generally compatible.
No specific contraception required.
DailyMed/FDA (NIH/NLM) — approved Fosfomycin trometamol label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=4f206750-8126-99a3-e063-6294a90ade4c
Clinical and educational support tool. The information does not replace a medical prescription or the opinion of a qualified healthcare professional.
Broad-spectrum antibiotic (phosphonic acid derivative), bactericidal, used as a single 3 g oral dose for acute uncomplicated cystitis in women; well tolerated, with diarrhoea as the most frequent effect.
Inhibits enolpyruvyltransferase (MurA), blocking peptidoglycan synthesis (first step of cell wall biosynthesis) — broad-spectrum bactericidal against Gram-positives and Gram-negatives, including E. coli and E. faecalis.
Rapid absorption: absolute oral bioavailability 37% fasting (30% with food); Cmax 26.1±9.1 mcg/mL ~2 h after 3 g (17.6 mcg/mL at 4 h with a high-fat meal); volume of distribution 136.1 L; distributes to the kidney, bladder wall, prostate and seminal vesicles.
Minimal metabolism; excretion unchanged in urine (~38% of the oral dose) and faeces (~18%); total clearance 16.9 L/h and renal 6.3 L/h; no plasma protein binding.
Elimination half-life ~5.7 h after a 3 g oral dose (half-life prolonged in renal impairment); mean urinary concentration of 706 mcg/mL 2-4 h after dosing.
Medicines from the same therapeutic group (ATC classification) or the same pharmacological class.
