Nitrofurantoin

Question 1

How does Nitrofurantoin work?

Answer 1

Nitrofurantoin is metabolised (reduced) in bacterial cells by nitrofuran reductase. Its active metabolite damages bacterial DNA and causes cell death (bactericidal effect). Nitrofurantoin is active against the Gram-negative (e.g. Escherichia coli) and Gram-positive (Staphylococcus saprophyticus) organisms that commonly cause urinary tract infections.

Bacteria with reduced nitrofuran reductase activity are resistant to nitrofurantoin. Some organisms that are less common causes of urinary tract infection (such as klebsiella and proteus species) have intrinsic resistance to nitrofurantoin. It is relatively rare for E. coli to acquire nitrofurantoin resistance.

Question 2

Indications for Nitrofurantoin

Answer 2

Uncomplicated lower urinary tract infection (UTI), as a first-line antibiotic (alternatives are trimethoprim, amoxicillin). Nitrofurantoin is particularly suited to the treatment of UTI as it is effective against the common causative organisms, reaches therapeutic concentrations in urine through renal excretion, and is most bactericidal in acidic environments such as urine.

Question 3

Contraindications for Nitrofurantoin

Answer 3

Nitrofurantoin should not be prescribed for pregnant women towards term or for babies in the first 3 months of life. It is contraindicated in patients with renal impairment, as impaired excretion increases toxicity and reduces efficacy due to lower urinary drug concentrations. Caution is required when using nitrofurantoin for long-term prevention of UTIs, as chronic use increases the risk of adverse effects, particularly in elderly patients.

Question 4

Side effects of Nitrofurantoin

Answer 4

As with many antibiotics, nitrofurantoin can cause gastrointestinal upset (including nausea and diarrhoea) and immediate and delayed hypersensitivity reactions (see Penicillins, broad-spectrum).

Nitrofurantoin specifically can turn urine dark yellow or brown.

Less commonly, it may cause chronic pulmonary reactions (including inflammation [pneumonitis] and fibrosis), hepatitis and peripheral neuropathy, which all are more likely with prolonged administration. In neonates, haemolytic anaemia may occur because immature red blood cells are unable to mop up nitrofurantoin-stimulated superoxides, which damage red blood cells.

Question 5

Interactions of Nitrofurantoin

Answer 5

No significant interactions

Question 6

Elimination of Nitrofurantoin

Answer 6

Renal

Question 7

Patient information on Nitrofurantoin

Answer 7

Oral nitrofurantoin is available as tablets, capsules and in suspension. It should be taken with food or milk to minimise gastrointestinal effects.

Explain that the aim of treatment is to get rid of infection and improve symptoms. Encourage the patient to complete the prescribed course. Before prescribing, always check with your patient personally or get collateral history to ensure that they do not have an allergy to nitrofurantoin. Advise them that their urine colour may change to dark yellow or brown during treatment; this is harmless and temporary. In long-term treatment, warn patients to report any unexplained symptoms, particularly pins and needles or breathlessness, which could indicate serious side effects.