Zithromax (Azithromycin)

How does it work?

Zithromax capsules and suspension contain the active ingredient azithromycin, which is a type of medicine called a macrolide antibiotic. Azithromycin is also available without a brand name, ie as the generic medicine. Azithromycin is used to treat infections caused by bacteria.

Azithromycin works by preventing bacteria from producing proteins that are essential to them. Without these proteins the bacteria cannot grow, replicate and increase in numbers. Azithromycin therefore stops the spread of infection and remaining bacteria are killed by the body's immune system or eventually die.

Azithromycin is a broad-spectrum antibiotic that is active against a wide variety of bacteria that cause a wide variety of infections. Azithromycin may be used to treat infections of the upper or lower airways, skin or soft tissue, or ears. It is also used to treat the sexually-transmitted infection chlamydia.

To make sure the bacteria causing an infection are susceptible to azithromycin your doctor may take a tissue sample, for example a swab from the throat or skin.

What is it used for?

  • Bacterial infection of the lungs and airways (chest or lower respiratory tract infection) eg pneumonia, bronchitis.
  • Bacterial infections of the nasal passages, sinuses or throat (upper respiratory tract infection) eg sinusitis, tonsillitis, pharyngitis.
  • Bacterial infections of the middle ear (otitis media).
  • Bacterial infections of the skin or soft tissue.
  • Chlamydia.
  • Uncomplicated gonorrhoea (unlicensed use).
  • Mild or moderate typhoid due to multiple-antibacterial-resistant organisms (unlicensed use).
  • Lyme disease (unlicensed use).

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 and your age. 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.
  • Azithromycin is usually taken once a day. Try and take it at the same time each day.
  • For the treatment of chlamydia only one dose is needed.
  • Zithromax capsules should be taken at least one hour before or two hours after food.
  • Zithromax suspension can be taken either with or without food.
  • Bottles of suspension should be shaken before measuring out a dose. Only use the measuring spoon provided with the suspension. You should not use a regular teaspoon or tablespoon to take the medicine, as this will not give an accurate dose.
  • Do not take indigestion remedies at the same time of day as azithromycin. This is because indigestion remedies can affect the absorption of azithromycin from the gut.
  • If you forget to take a dose take it as soon as you can that day. Then take your next dose at the right time the following day. Do not 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.


  • Broad-spectrum antibiotics can sometimes cause inflammation of the bowel (colitis). For this reason, if you get diarrhoea that becomes severe or persistent or contains blood or mucus, either during or after taking this medicine, you should consult your doctor immediately.
  • All antibiotics can sometimes result in overgrowth of organisms that are not susceptible to the antibiotic, in particular fungi. You should let your doctor know if you think you have developed any other infection, for example thrush, while you are taking this medicine, so that it can be treated appropriately.
  • Zithromax suspension can be stored at room temperature. Any suspension remaining after 5 days should be disposed of, preferably by returning it to your pharmacist.

Use with caution in

  • People with severely decreased kidney function.
  • People with liver disease (azithromycin should be avoided where possible in people with severe liver disease).
  • People with heart problems such as heart failure or irregular heartbeats (arrhythmias).
  • People with a slow heartbeat (bradycardia).
  • People with an abnormal heart rhythm seen on a heart monitoring trace (ECG) as a 'prolonged QT interval'.
  • People taking medicines that can prolong the QT interval (your doctor will know, but see the end of this factsheet for some examples).
  • People with disturbances in the levels of electrolytes such as potassium and magnesium in their blood.
  • People with a condition called myasthenia gravis, where there is abnormal muscle weakness.
  • People with diabetes should be aware that Zithromax suspension contains sucrose. For this reason it may also not be suitable for people with hereditary problems of fructose intolerance.

Not to be used in

  • Children under six months of age.
  • People who are allergic to other macrolide or ketolide type antibiotics, eg erythromycin, clarithromycin.
  • Zithromax capsules are not suitable for children weighing under 45kg. The suspension should be used for children who weigh under 45kg.
  • Zithromax capsules contain lactose and are not suitable for people with rare hereditary problems of galactose intolerance, the Lapp lactase deficiency or glucose-galactose malabsorption.

This medicine should not be used if you are allergic to one or 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.

  • The safety of this medicine for use during pregnancy has not been established. It is not recommended for use in pregnancy unless considered essential by your doctor. Seek medical advice from your doctor.
  • This medicine passes into breast milk. It is not recommended for use during breastfeeding unless considered essential by your doctor. Seek medical advice from your doctor.

Label warnings

  • Do not take indigestion remedies at the same time of day as this medication.
  • Take at regular intervals. Complete the prescribed course unless otherwise directed.

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 does not mean that all people using this medicine will experience that or any side effect.

Very common (affect more than 1 in 10 people)

  • Disturbances of the gut such as diarrhoea, nausea, abdominal pain or wind.

Common (affect between 1 in 10 and 1 in 100 people)

  • Vomiting.
  • Indigestion.
  • Loss of appetite.
  • Dizziness.
  • Headache.
  • Fatigue.
  • Pins and needles sensations (paraesthesia).
  • Pain in the joints (arthralgia).
  • Rash or itching.
  • Taste disturbances.
  • Disturbances in vision or hearing.

Uncommon (affect between 1 in 100 and 1 in 1000 people)

  • Feeling weak or generally unwell.
  • Oral or vaginal thrush infections (candidiasis - see warning section above).
  • Constipation.
  • Inflammation of the stomach (gastritis).
  • Sleepiness.
  • Difficulty sleeping (insomnia).
  • Reduced sensation or numbness (hypoaesthesia).
  • Increased sensitivity of the skin to sunlight.
  • Nervousness.
  • Awareness of your heartbeat (palpitations).
  • Chest pain.
  • Swelling due to fluid retention (oedema).
  • Inflammation of the liver (hepatitis).
  • Decrease in the number of white blood cells in the blood.

Rare (affect between 1 in 1000 and 1 in 10,000 people)

  • Sensation of spinning (vertigo).
  • Agitation.
  • Abnormal reaction of the skin to light, usually a rash (photosensitivity).
  • Abnormal liver function.

Frequency unknown

  • Inflammation of the large intestine (colitis) - see warning section above.
  • Abnormal heart beats (arrhythmias).
  • Inflammation of the pancreas (pancreatitis).
  • Tongue discolouration.
  • Decrease in the number of platelets in the blood (thrombocytopenia).
  • Aggression.
  • Anxiety.
  • Low blood pressure.
  • Fainting.
  • Seizures (convulsions).
  • Muscle weakness.
  • Reduced sense of smell.
  • Liver or kidney failure.
  • Severe skin reactions.

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.

This medicine should not be taken by people taking ergotamine or related medicines, eg dihydroergotamine or methysergide (used to treat migraine).

Antacids for indigestion and heartburn reduce the absorption of azithromycin from the gut if they are taken at the same time as azithromycin. Antacids should not be taken in the two hours before and after taking azithromycin.

Azithromycin may reduce the breakdown of the medicines listed below. If the blood levels of these medicines are raised as a result, it may lead to an increased risk of their side effects. If you are taking one of these medicines and are prescribed azithromycin you should let your doctor or pharmacist know if you experience any new or increased side effects:

  • ciclosporin
  • colchicine
  • digoxin
  • disopyramide
  • droperidol
  • mizolastine
  • pimozide
  • quetiapine
  • reboxetine
  • rifabutin
  • theophylline.

If you are taking digoxin or ciclosporin it is recommended that your blood levels are monitored while you are taking a course of azithromycin. Your doctor may adjust your digoxin or ciclosporin dose if necessary.

The manufacturers of droperidol, mizolastine, pimozide and reboxetine state that macrolide antibiotics such as this one are not recommended for people taking these medicines.

Azithromycin may enhance the anti-blood-clotting effects of warfarin and possibly other anticoagulant medicines. If you are taking an anticoagulant your doctor may want to perform extra monitoring of your blood clotting time (INR) while you are also taking azithromycin.

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 the vaccine less effective.

Nelfinavir may increase the amount of azithromycin in the blood. If you regularly take nelfinavir you should tell your doctor if you experience any new side effects while taking a course of azithromycin.

There may be an increased risk of abnormal heart beats if clarithromycin is taken in combination with any of the following medicines:

  • anti-arrhythmic medicines (for an irregular heartbeat), eg amiodarone, disopyramide, quinidine
  • certain antimalarials, eg chloroquine, quinine, mefloquine, halofantrine
  • certain antipsychotics, eg chlorpromazine, thioridazine, fluphenazine, haloperidol.

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


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