Pharmacology · Urinary antiseptics
Nitrofurantoin !
A first-line oral drug for uncomplicated cystitis that acts only in the bladder. Long courses can harm the lungs, liver and nerves.
Updated 2026-11-01
Mechanism of action
Bacterial flavoproteins reduce nitrofurantoin to reactive intermediates that attack ribosomal proteins and other macromolecules, disrupting protein synthesis, metabolism and cell-wall building. Because several targets are hit at once, resistance develops slowly. It reaches useful levels only in urine.
- Filtered and concentrated in the urine
- Bacterial flavoproteins reduce it
- Reactive products damage ribosomes and enzymes
- Bacteria in the bladder die
Pharmacokinetics
- Absorption
- Absorbed by mouth; food increases absorption and tolerance.
- Distribution
- Low blood and tissue levels; high in urine.
- Elimination
- Urine, partly unchanged; it can turn the urine brown.
Indications
- Acute uncomplicated cystitis (WHO «Access» antibiotic) Urinary tract infection (acute cystitis) →
- Prevention of recurrent urinary tract infection in selected patients
Adverse effects
Common
- Nausea, loss of appetite and headache
- Brown urine
- Rash
Contraindications
- Significantly reduced kidney function, oliguria or anuria (too little reaches the urine and toxicity rises)
- Pregnancy at term (38–42 weeks), labour and delivery, and newborns under one month (haemolysis)
- Previous cholestatic jaundice or liver dysfunction with nitrofurantoin
Key interactions
- Antacids with magnesium trisilicate
- Reduce absorption.
- Probenecid and other uricosurics
- Block its tubular secretion: lower urinary levels and more toxicity.
What is monitored
- Breathing symptoms and chest findings, especially with long-term use
- Liver tests and kidney function in long courses
- Numbness or tingling
Administration and safety
- Given with food to improve absorption and reduce nausea
- Capsules are swallowed whole
- Not used for pyelonephritis or bloodstream infection
Nursing care
- Explain that brown urine is harmless
- Teach to report cough, breathlessness, fever, yellow skin or tingling
- Check kidney function before starting
- Ask about pregnancy stage
Pregnancy and breastfeeding
Used for cystitis in pregnancy, but avoided at term, during labour and near delivery because of newborn haemolysis.
Test yourself
Think of the answer, then tap the question to see it.
Why is nitrofurantoin not used for pyelonephritis?
It reaches useful levels only in the bladder urine, not in kidney tissue or blood.
Which lung problem can appear with long-term nitrofurantoin?
Chronic interstitial pneumonitis or pulmonary fibrosis.
Why is it contraindicated at the end of pregnancy?
It can cause haemolytic anaemia in the newborn, whose red cells are vulnerable.
Related drugs
Related conditions
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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: DailyMed - NITROFURANTOIN- MONOHYDRATE/MACROCRYSTALS capsule (DailyMed (U.S. National Library of Medicine), 2026); Nitrofurantoin: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); eEML - Electronic Essential Medicines List (World Health Organization, 2025).
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Representative model, for educational purposes only.