Nitrofurantoin

Urinary Antiseptic·Infectious Diseases - Urinary Agents

Acute uncomplicated lower urinary tract infections (cystitis), prophylaxis of recurrent UTI

PBSANTIBIOTICMacrodantin (IR), Macrobid (MR)50 mgS4+1

Max Dose

400 mg/day

Half-life

20 mins

Lung Tox

CHRONIC USE

eGFR < 30

CONTRAIND.

Rapid Summary

Overview

Urinary antiseptic. Rapidly concentrates in the bladder to kill E. coli. Useless for systemic infections. Highly effective for simple cystitis.

Maximum Dose

Max 400 mg/day (100 mg QID for acute flares).

Clinical Focus

Completely ineffective if eGFR < 30 because it cannot reach the bladder. Long-term use causes fatal pulmonary fibrosis.

Bottom Line

Nitrofurantoin is a first-line antibiotic for uncomplicated lower UTIs with low resistance rates, but is contraindicated if eGFR < 30 and can cause pulmonary fibrosis with long-term use.

Formulation & Access

Brand Names

Macrodantin (IR), Macrobid (MR)

Oral Routes

Take with food

Capsules (50 mg, 100 mg). Take with food to boost absorption and reduce nausea.

Prescribing & PBS

Unrestricted General Benefit (S4).

Indications & Use

Primary

PBSTGA

Acute uncomplicated lower urinary tract infections (cystitis), prophylaxis of recurrent UTI.

Clinical Place

First-line oral agent for female cystitis. Highly resistant to resistance-building.

Quick reference

Class & Role

Urinary Antiseptic — Urinary antiseptic.

Route / Formulation

Capsules (50 mg, 100 mg). Take with food to boost absorption and reduce nausea. (Macrodantin (IR), Macrobid (MR))

Usual Dose & Max

PO 100 mg QID (or 100 mg BD for the modified-release macrocrystal form) for 5 days. Max 400 mg/day (100 mg QID for acute flares).

Key Indication Doses

Acute Uncomplicated UTI: PO 100 mg QID (or 100 mg BD for the modified-release macrocrystal form) for 5 days. UTI Prophylaxis: PO 50-100 mg NOCTE. Renal Impairment: Avoid if eGFR < 30 (Drug pools in blood causing severe toxicity, and zero drug reaches the urine to kill the bacteria).

Best Uses

Nitrofurantoin is a first-line antibiotic for uncomplicated lower UTIs with low resistance rates, but is contraindicated if eGFR < 30 and can cause pulmonary fibrosis with long-term use.

Avoid / Cautions

eGFR < 30, history of pulmonary toxicity, late pregnancy (near term). Pregnancy Category A (Safe in early pregnancy, but avoid at 38+ weeks due to risk of neonatal hemolytic anemia).

Key Risks

Respiratory: Nitrofurantoin-induced pulmonary toxicity. Can be acute (hypersensitivity pneumonitis) or chronic (irreversible pulmonary fibrosis after ~6 months of use). Neurological: Peripheral neuropathy (especially in renal failure where the drug accumulates in the blood). Gastrointestinal: Nausea, vomiting, anorexia (take with food to mitigate). Haematological: Hemolytic anemia (in G6PD deficiency).

Key Interactions

Antacids containing magnesium delay absorption. Antagonises the action of nalidixic acid (rarely used).

Monitoring

Check eGFR before prescribing. For patients on chronic prophylaxis, review every 3-6 months. Ask about dry cough or shortness of breath (Pulmonary fibrosis).

Clinical Pearl

Nitrofurantoin does NOT penetrate renal tissue or blood. It only acts in the bladder pool. NEVER use it to treat pyelonephritis or urosepsis. The patient will die of sepsis while having sterile urine.

Access

Macrodantin (IR), Macrobid (MR)50 mg

Brand: Macrodantin (IR), Macrobid (MR)
Formulation: Capsules (50 mg, 100 mg)

Nitrofurantoin

Urinary Antiseptic·Infectious Diseases - Urinary Agents

Acute uncomplicated lower urinary tract infections (cystitis), prophylaxis of recurrent UTI

PBSANTIBIOTICMacrodantin (IR), Macrobid (MR)50 mgS4+1

Max Dose

400 mg/day

Half-life

20 mins

Lung Tox

CHRONIC USE

eGFR < 30

CONTRAIND.

Rapid Summary

Overview

Urinary antiseptic. Rapidly concentrates in the bladder to kill E. coli. Useless for systemic infections. Highly effective for simple cystitis.

Maximum Dose

Max 400 mg/day (100 mg QID for acute flares).

Clinical Focus

Completely ineffective if eGFR < 30 because it cannot reach the bladder. Long-term use causes fatal pulmonary fibrosis.

Bottom Line

Nitrofurantoin is a first-line antibiotic for uncomplicated lower UTIs with low resistance rates, but is contraindicated if eGFR < 30 and can cause pulmonary fibrosis with long-term use.

Formulation & Access

Brand Names

Macrodantin (IR), Macrobid (MR)

Oral Routes

Take with food

Capsules (50 mg, 100 mg). Take with food to boost absorption and reduce nausea.

Prescribing & PBS

Unrestricted General Benefit (S4).

Indications & Use

Primary

PBSTGA

Acute uncomplicated lower urinary tract infections (cystitis), prophylaxis of recurrent UTI.

Clinical Place

First-line oral agent for female cystitis. Highly resistant to resistance-building.

Quick reference

Class & Role

Urinary Antiseptic — Urinary antiseptic.

Route / Formulation

Capsules (50 mg, 100 mg). Take with food to boost absorption and reduce nausea. (Macrodantin (IR), Macrobid (MR))

Usual Dose & Max

PO 100 mg QID (or 100 mg BD for the modified-release macrocrystal form) for 5 days. Max 400 mg/day (100 mg QID for acute flares).

Key Indication Doses

Best Uses

Nitrofurantoin is a first-line antibiotic for uncomplicated lower UTIs with low resistance rates, but is contraindicated if eGFR < 30 and can cause pulmonary fibrosis with long-term use.

Avoid / Cautions

eGFR < 30, history of pulmonary toxicity, late pregnancy (near term). Pregnancy Category A (Safe in early pregnancy, but avoid at 38+ weeks due to risk of neonatal hemolytic anemia).

Key Risks

Key Interactions

Antacids containing magnesium delay absorption. Antagonises the action of nalidixic acid (rarely used).

Monitoring

Check eGFR before prescribing. For patients on chronic prophylaxis, review every 3-6 months. Ask about dry cough or shortness of breath (Pulmonary fibrosis).

Clinical Pearl

Access

Macrodantin (IR), Macrobid (MR)50 mg

Brand: Macrodantin (IR), Macrobid (MR)
Formulation: Capsules (50 mg, 100 mg)