Before starting

Consider

• Baseline
  • Estimated glomerular filtration rate
  • G6PD deficiency · contraindicated if deficiency
  • Liver function tests
  • Porphyria · contraindicated

Interpreting renal function

Contraindicated if eGFR is less than 30mL/minute/1.73m².
If eGFR less than 45 mL/min/1.73m², normally avoid unless used with caution as a short course only (3 to 7 days). Indications include uncomplicated lower urinary tract infection caused by suspected or proven multi-drug resistant bacteria where benefit outweighs risk.

Continued until stable

Consider

• Periodically
  • Estimated glomerular filtration rate · long-term treatment contraindicated if less than 45mL/minute/1.73m²
  • Liver function tests · cholestatic jaundice can occur with short-term (2 week) therapy
  • Pulmonary symptoms · especially important in elderly

Ongoing once stable

Consider

• Periodically
  • Estimated glomerular filtration rate · long-term treatment contraindicated if less than 45mL/minute/1.73m²
  • Liver function tests · chronic active hepatitis, occasionally leading to hepatic necrosis, is possible with long-term (greater than 6 months) therapy
  • Pulmonary symptoms · especially important in elderly

Abnormal results

Respond to results and symptoms

Consider stopping if the person develops unexplained:

• pulmonary symptoms: identifying effects and taking action early will positively affect outcome. Minor symptoms such as fever, chills, cough and dyspnoea may be significant and should be investigated. It is possible that pulmonary function may be impaired permanently, even after cessation of therapy.
• hepatotoxicity
• haematological toxicity
• neurologic syndrome

Urinary effects

People taking nitrofurantoin are susceptible to false positive urinary glucose (if tested for reducing substances).

Notes

Advice to patients

Advise patients to report any signs or symptoms of:

• pulmonary toxicity (e.g. cough; chest pain; dyspnoea)
• hepatotoxicity (note onset can be insidious and non-specific: e.g. nausea, rash, headache, flu-like symptoms)
• peripheral neuropathy (sensory as well as motor involvement)
• haemolysis

Bibliography

• Mercury Pharmaceuticals Ltd. Summary of Product Characteristics – Nitrofurantoin 100mg Capsules. Last revised 11/2018 [cited 11/06/2020]
• NICE Clinical Knowledge Summaries (CKS). Urinary tract infection – lower (women). Updated Jul 2018 [cited 30/07/2020]
• Medicines and Healthcare products Regulatory Agency. Nitrofurantoin now contraindicated in most patients with an estimated glomerular filtration rate (eGFR) of less than 45ml/min/1.73m2. Drug Safety Update volume 8 issue 2, September 2014: A3 [cited June 2020]
• Joint Formulary Committee. British National Formulary (online) London: BMJ Group and Pharmaceutical Press [cited 11/06/2020]