Macrobid (Nitrofurantoin)

How does it work?

Macrobid prolonged-release capsules contain the active ingredient nitrofurantoin, which is a type of medicine called an antibiotic. Antibiotics are used to treat infections caused by bacteria. Nitrofurantoin is also available without a brand name, ie as the generic medicine.

Nitrofurantoin is filtered out of the blood and into the urine by the kidneys. High levels of the medicine pass into the urine, which means that nitrofurantoin can be used to treat bacterial infections in the urinary tract.

Nitrofurantoin works by killing the bacteria that are causing an infection. It does this by entering the bacterial cells and damaging the genetic material (DNA) of the bacteria. This means that the bacteria cannot reproduce and repair themselves. This kills the bacteria and controls the infection.

Your doctor may ask you for a urine sample to make sure the bacteria causing the infection are susceptible to nitrofurantoin.

Macrobid capsules are prolonged-release capsules, which means they are designed to release the medicine slowly over a few hours. This type of capsule should be swallowed whole and not opened, crushed or chewed, as this would damage the prolonged-release action.

What is it used for?

  • Treatment of urinary tract infections.
  • Prevention of recurrent lower urinary tract infections.

How do I take it?

  • The dose of this medicine and how long it needs to be taken for depends on the type of infection you have. Follow the instructions given by your doctor. These will be printed on the dispensing label that your pharmacist has put on the packet of medicine.
  • Macrobid capsules are usually taken twice a day (every 12 hours). You should try to space the doses evenly.
  • Macrobid capsules should be swallowed whole and not opened, crushed or chewed. They should be taken with or just after a meal. This helps to minimise any stomach upset that may be caused by the medicine and also helps it to be absorbed.
  • If you forget to take a dose take it as soon as you remember, unless it is nearly time for you next dose. In this case leave out the missed dose and just take the next scheduled dose as usual. Don't take a double dose to make up for a missed dose.
  • Unless your doctor tells you otherwise, it is important that you finish the prescribed course of this antibiotic medicine, even if you feel better or it seems the infection has cleared up. Stopping the course early increases the chance that the infection will come back and that the bacteria will grow resistant to the antibiotic.


  • This medicine can turn your urine a dark yellow or brown colour. This is normal and nothing to worry about - it is due to the colour of the medicine.
  • This medicine may interfere with certain urine tests for glucose, causing the test to give a "false positive" result (ie, the test may say that glucose is present in the urine even if it is not). If you need to test your urine for glucose while taking this medicine you should ask your pharmacist for advice on which test to use.
  • Tell your doctor if you experience any of the following side effects while taking this medicine, as your treatment may need to be stopped: signs of nerve problems such as pins and needles or tingling type sensations; signs of possible lung problems such as fever, shivering, cough, shortness of breath or a blue colouring to your skin; or signs of possible liver problems such as, yellowing of the skin or whites of the eyes (jaundice).
  • If you need to take this medicine long-term it is recommended that you are regularly monitored by your doctor. Your doctor may want to carry out tests to check for side effects, particularly those that can affect your lungs or liver.

Use with caution in

  • People with decreased liver function or liver disease.
  • People with lung disease.
  • Anaemia.
  • Diabetes.
  • People with folate deficiency.
  • People with vitamin B deficiency.
  • People with disturbances in the levels of salts (electrolytes such as sodium, magnesium or calcium) in their blood.
  • People with disorders of the nerves.

Not to be used in

  • People with decreased kidney function.
  • People who a lack an enzyme called G6PD in their blood.
  • Hereditary blood disorders called porphyrias.
  • Pregnant women at term (during labour and childbirth).
  • Macrobid prolonged-release capsules are not suitable for children under 12 years of age.

This medicine should not be used if you are allergic to any of its ingredients. Please inform your doctor or pharmacist if you have previously experienced such an allergy.

If you feel you have experienced an allergic reaction, stop using this medicine and inform your doctor or pharmacist immediately.

Pregnancy and breastfeeding

Certain medicines should not be used during pregnancy or breastfeeding. However, other medicines may be safely used in pregnancy or breastfeeding providing the benefits to the mother outweigh the risks to the unborn baby. Always inform your doctor if you are pregnant or planning a pregnancy, before using any medicine.

  • Nitrofurantoin should not be used by pregnant women at term (during labour and childbirth) as this could affect the red blood cells of the baby. However the medicine is not known to be harmful if used during earlier pregnancy. As with all medicines you should get medical advice from your doctor before taking this medicine if you are pregnant.
  • This medicine passes into breast milk. It should not be used by women who are breastfeeding. Seek further medical advice from your doctor.

Label warnings

  • Take at regular intervals. Complete the prescribed course unless otherwise directed.
  • Take this medication with or after food.
  • This medication may cause your urine to be coloured.

Side effects

Medicines and their possible side effects can affect individual people in different ways. The following are some of the side effects that are known to be associated with this medicine. Just because a side effect is stated here, it does not mean that all people using this medicine will experience that or any side effect.

  • Nausea and vomiting.
  • Abdominal pain.
  • Diarrhoea.
  • Loss of appetite.
  • Yellow or brown colouration of urine.
  • Disorder of the peripheral nerves causing pins and needles or tingling sensations, weakness or numbness (peripheral neuropathy). Tell your doctor straight away if you experience these problems.
  • Drowsiness.
  • Dizziness.
  • Liver problems such as inflammation of the liver (hepatitis) or yellowing of the skin and whites of the eyes (jaundice). Tell your doctor if you notice this.
  • Acute or chronic lung reactions, with symptoms such as fever, shivering, shortness of breath, cough or chest pain. Tell your doctor straight away if you get any of these symptoms.
  • Allergic reactions, such as severe swelling of lips, face or tongue (angioedema), or itchy, blistering rashes.
  • Blood disorders.
  • Temporary hair loss.
  • Raised pressure in the skull (causing severe headaches - tell your doctor if you experience this).

The side effects listed above may not include all of the side effects reported by the medicine's manufacturer.

For more information about any other possible risks associated with this medicine, please read the information provided with the medicine or consult your doctor or pharmacist.

How can this medicine affect other medicines?

It is important to tell your doctor or pharmacist what medicines you are already taking, including those bought without a prescription and herbal medicines, before you start treatment with this medicine. Similarly, check with your doctor or pharmacist before taking any new medicines while taking this one, to make sure that the combination is safe.

Antacids (remedies for indigestion and heartburn) that contain magnesium salts such as magnesium trisilicate may reduce the absorption of nitrofurantion from the gut, which could make it less effective. If you need to take an antacid you should take it at least two hours before or two hours after taking your nitrofurantoin dose.

Nitrofurantion may be less effective at treating urinary tract infections if it is taken in combination with probenecid or sulfinpyrazone, because these medicines decrease the excretion of nitrofurantion into the urine. This could also increase the risk of nitrofurantoin side effects.

Oral typhoid vaccine (Vivotif) should not be taken until at least three days after you have finished a course of this antibiotic, because the antibiotic could make this vaccine less effective.

In the past, women using hormonal contraception such as the pill or patch would be advised to use an extra method of contraception (eg condoms) while taking an antibiotic like this one and for seven days after finishing the course. However, this advice has now changed. You no longer need to use an extra method of contraception with the pill, patch or vaginal ring while you take a course of antibiotics. This change in advice comes because to date there is no evidence to prove that antibiotics (other than rifampicin or rifabutin) affect these contraceptives. This is the latest guidance from the Faculty of Sexual & Reproductive Healthcare.

However, if you are taking the contraceptive pill and experience vomiting or diarrhoea as a result of taking this antibiotic, you should follow the instructions for vomiting and diarrhoea described in the leaflet provided with your pills.

Other medicines containing the same active ingredient

  • Furadantin.
  • Macrodantin.

Nitrofurantoin tablets and oral suspension are also available without a brand name, ie as the generic medicine.