A macrolide antibiotic
Azithromycin
A macrolide antibiotic taken as a short course for chest, throat and some sexually transmitted infections, and a common alternative for people allergic to penicillin.
What is Azithromycin?
Azithromycin is a macrolide antibiotic used for a range of infections, including some chest, throat, ear, skin and sexually transmitted infections. A useful feature is that a short course can keep working for several days after it is finished.
Education and reference only. This is a plain-language guide to Azithromycin — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Azithromycin is a macrolide antibiotic used for a range of infections, including some chest, throat, ear, skin and sexually transmitted infections. A useful feature is that it stays in the body for some time after the last dose, so it is often given as a short course rather than over many days. It is a frequent alternative for people who are allergic to penicillin. In the UK and US it is sold under the brand Zithromax, alongside generic versions.
How it works
Azithromycin attaches to the bacterial ribosome — the machinery bacteria use to build proteins — and stops them from making the proteins they need to grow and multiply. With protein production blocked, the bacteria stop spreading and the body's immune system can clear the infection. Azithromycin concentrates inside body tissues and lingers there, which is why a short course can keep working after the tablets have finished.
Company & origin
Originated / developed by: Pliva (Croatia; licensed to Pfizer).
Azithromycin was discovered in 1980 by a team led by Slobodan Djokic at the Croatian company Pliva, which patented it and marketed it as Sumamed (1988); Pliva licensed it to Pfizer, which sold it as Zithromax from 1991.
Practical use
How to take Azithromycin
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Take it as prescribed and complete the course, even though it may be short, to fully treat the infection.
- It can be taken with or without food; if it upsets your stomach, taking it with food may help.
- Separate it from indigestion remedies containing aluminium or magnesium, which can reduce absorption.
- Tell your doctor about heart-rhythm problems or other medicines, as it can affect the heart's electrical activity.
- Report severe or persistent diarrhoea, which should be assessed rather than self-treated.
- Finish the whole course and do not save any for later use.
Weighing it up
Advantages & disadvantages of Azithromycin
Advantages
- Short, convenient courses that keep working after the last dose.
- Useful for several common and sexually transmitted infections.
- Can be taken with or without food.
- Generally well tolerated.
Disadvantages
- Can cause nausea, diarrhoea and stomach upset.
- Can prolong the heart's QT interval and affect heart rhythm.
- Overuse contributes to antibiotic resistance.
- Not effective against viral infections such as colds and flu.
Practical use
Good to know
Azithromycin is usually taken as a short course, sometimes just once. It is a common choice when someone is allergic to penicillin. Like other macrolides it can affect the heart's electrical rhythm (QT prolongation), so care is needed in people with heart-rhythm risks or taking other medicines that do the same. It generally interacts less with statins than other macrolides such as clarithromycin and erythromycin, but it can still increase the effect of warfarin, so any unexpected bruising or bleeding should be reported. Finish the full course even if you feel better.
Who should not take it / use with caution
- People who have had a serious allergic reaction to azithromycin or another macrolide antibiotic.
- Used with caution in people with significant liver disease, certain heart-rhythm problems (such as a long QT interval), or low blood potassium or magnesium.
- Care in pregnancy and breastfeeding, and alongside other medicines that affect heart rhythm — used when the benefit is judged to outweigh the risk.
Monitoring
- Response of the infection
- Heart-rhythm risk in those predisposed
- INR if taken with warfarin
Side effects
- Nausea, diarrhoea, tummy cramps and feeling sick are the most common effects.
- Headache, altered taste, or temporary changes in liver blood tests.
- Rarely, heart-rhythm changes (QT prolongation), serious skin reactions, hearing changes, or serious gut infection (Clostridioides difficile) — seek advice if these occur.
Key interactions
- Other medicines that affect heart rhythm (QT prolongation) add to that risk and need care.
- It can increase the effect of warfarin, raising bleeding risk, so monitoring may be needed.
- Indigestion remedies containing aluminium or magnesium can reduce its absorption if taken at the same time; it interacts with statins less than other macrolides but caution still applies.
Available as: Tablets, capsules, a liquid (suspension) for children and those who cannot swallow tablets, and forms given by drip in hospital. Eye drops also exist for certain eye infections.
Answers
Azithromycin: frequently asked questions
Why is azithromycin often a short course?
Azithromycin builds up inside body tissues and keeps working for some days after the last dose, so a short course can be enough to treat the infection. Always take exactly the course you are prescribed, even if it seems brief — it is designed to keep acting after you finish.
Can I take azithromycin if I am allergic to penicillin?
Yes — macrolides like azithromycin are chemically unrelated to penicillin, so they are a common alternative for people with a penicillin allergy. Tell your prescriber about all your allergies so the safest choice is made.
Does azithromycin affect the heart?
Like other macrolides, azithromycin can occasionally affect the heart's electrical rhythm (a change called QT prolongation). This is uncommon but matters more in people with existing heart-rhythm problems or taking other medicines that do the same, so always share your full medicine list.
Can I take it with my other medicines?
Azithromycin interacts less with statins than other macrolides, but it can increase the effect of warfarin and adds to the risk from other rhythm-affecting medicines. Run your medicines, including over-the-counter ones, past your pharmacist before starting.
What is the difference between azithromycin and Zithromax?
They are the same medicine — azithromycin is the generic (active-ingredient) name and Zithromax is a brand name. Generic azithromycin contains the identical active ingredient.
The wider class
About Macrolide antibiotics
Azithromycin belongs to the macrolide antibiotics class. For how the class as a whole works, its shared safety principles and monitoring, see the full guide.
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Authoritative sources
- BNF: Azithromycin.
- electronic Medicines Compendium (SmPC): Azithromycin (Zithromax).
- NICE CKS: Azithromycin.
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