Nitrofurantoin

What it is

Nitrofurantoin is an antibacterial that concentrates in the urine rather than in the bloodstream. Bacteria reduce it into reactive compounds that damage their DNA, ribosomes and enzymes at several points at once. It is used for bacterial infections of the bladder and lower urinary tract, and is not suitable for infections elsewhere in the body.

A usual adult range, not a national label — the dose and the timing differ by country and by product.

Used for

• Bacterial infection

Approved uses differ by country — some of these may be off-label or unapproved where you live.

What to know while taking it

It is taken with food, which improves absorption and reduces stomach upset. The urine commonly turns dark yellow or brown, which is expected and not a sign of harm. Because the drug has to be filtered into the urine to work, reduced kidney function both weakens it and lets it accumulate, so creatinine and eGFR are checked when kidney disease is present; ALT may also be followed, as the liver is occasionally affected. The full course is completed even once symptoms settle, or the infection can return.

When to see a doctor

See a doctor for new shortness of breath, a dry cough, chest pain or fever, especially during long-term use, as lung reactions are a recognised though rare problem. Numbness or tingling in the limbs, yellowing of the skin or eyes, or symptoms that do not improve also need review.

Worth knowing

• Caution with kidney disease
• Finish the full course
• Rare lung reactions on long use

Markers to watch

• Creatinine
• eGFR
• ALT