A macrolide antibiotic that stops bacteria making proteins, given as a short course (often three days) for chest, ear, sinus, skin and sexually transmitted infections and as an alternative in penicillin allergy; long-lasting in tissues, with cautions about heart rhythm and interactions.
Capsules and tablets 250 and 500 mg, oral suspension; usually 500 mg once daily for 3 days, or a single 1 g dose for chlamydia; intravenous infusion in hospital
Onset and duration
Improvement expected within 2-3 days; tissue levels persist for 5-7 days after a 3-day course.
Azithromycin stops bacteria from making the proteins they need to grow and multiply. Your immune system then clears the weakened bacteria. It builds up inside cells and stays in the body for days, so a course can be as short as three days.
Bronchitis, pneumonia, sexually transmitted diseases and infections of the ears, lungs, sinuses, skin, throat and reproductive organs; prevention of disseminated MAC infection
NICE: an alternative first-choice for low-severity community-acquired pneumonia in penicillin allergy, and added to amoxicillin (or used as an alternative) for moderate severity
NICE: azithromycin prophylaxis (unlicensed) for people with frequent exacerbations despite optimised treatment, after ECG, liver function and sputum culture, with hearing monitoring
Licensed indications come from the product licence in the named country; guideline-supported and off-label uses are cited to the guideline that supports them. Licensing differs between countries.
How it works
Azithromycin stops bacteria from making the proteins they need to grow and multiply. Your immune system then clears the weakened bacteria. It builds up inside cells and stays in the body for days, so a course can be as short as three days.
Binds to the bacterial ribosome (the 50S subunit) and blocks the tunnel through which new proteins leave, so the bacterium cannot make the proteins it needs to grow. Human ribosomes are built differently and are not affected. Azithromycin is concentrated inside cells, particularly white cells, which carry it to sites of infection, and it lingers in tissues for days after the last dose, which is why courses are short. Because it barely interferes with the liver's drug-metabolising enzymes, it has fewer interactions than erythromycin and clarithromycin.
Mechanism of action
Azithromycin is an azalide macrolide that binds reversibly to the 23S rRNA of the bacterial 50S ribosomal subunit within the peptide exit tunnel, blocking translocation and elongation of the nascent polypeptide; the effect is mainly bacteriostatic, bactericidal against some organisms at high concentrations. It achieves intracellular and tissue concentrations many times those in plasma, is delivered by phagocytes to infected tissue and has a tissue half-life of 2-4 days, allowing 3- to 5-day courses and single-dose regimens. Its spectrum includes streptococci, Haemophilus, Moraxella, atypical respiratory pathogens (Mycoplasma pneumoniae, Chlamydia, Legionella), Chlamydia trachomatis and Mycobacterium avium complex; pneumococcal macrolide resistance is common in some regions. Unlike erythromycin and clarithromycin it is a weak inhibitor of CYP3A4, but it inhibits P-glycoprotein (raising digoxin levels) and, like all macrolides, can prolong the QT interval. Long-term low-dose use in COPD and bronchiectasis works partly through anti-inflammatory and immunomodulatory effects.
Diarrhoea, nausea, stomach pain, wind, loss of appetite
Headache, dizziness, altered taste
Thrush (oral or vaginal)
Serious: seek help
Allergic reactions including anaphylaxis and severe skin reactions
Heart rhythm disturbance from QT prolongation, particularly with other QT-prolonging drugs, low potassium or magnesium, or existing heart rhythm problems
Liver injury (jaundice, dark urine, pale stools)
Severe or persistent diarrhoea (Clostridioides difficile infection)
Worsening of myasthenia gravis; hearing loss with long courses
Source: NHS: Azithromycin. Frequencies follow the source's categories; no percentages are invented.
Serious safety information
Special warning. QT prolongation and arrhythmia: macrolides can prolong the QT interval and have been associated with torsades de pointes and sudden cardiac death; risk is higher with other QT-prolonging medicines, low potassium or magnesium, bradycardia, heart failure and congenital long QT. UK
Special warning. Severe allergic and skin reactions including anaphylaxis, angioedema, Stevens-Johnson syndrome and DRESS: UK information advises stopping and seeking urgent help for swelling, breathing difficulty or a blistering rash. UK
Special warning. Clostridioides difficile-associated diarrhoea can occur during or after treatment; severe or persistent diarrhoea needs assessment. UK
Warnings and precautions
Liver. Hepatotoxicity: abnormal liver function, hepatitis, cholestatic jaundice and rarely liver failure have been reported; stop and seek assessment for jaundice, dark urine or severe abdominal pain. UK
Other. Myasthenia gravis: macrolides can worsen muscle weakness; caution in people with myasthenia. UK
Monitoring. Long-term prophylaxis: baseline ECG (avoid if QTc is prolonged), liver function tests and hearing assessment, repeated during treatment; reviewed after 3 months and then at least every 6 months. UK
Contraindications
Factor
Detail
Strength
Country · source
Hypersensitivity to macrolides
Contraindicated with a history of allergy to azithromycin, erythromycin, clarithromycin or any macrolide.
"Absolute" and "relative" follow the wording of the cited source; where the source does not classify, the cell is blank.
Interactions
Check interactions
Taking Azithromycin with other medicines? Add them to the checker to see what the official sources say about each pair: the mechanism, general management and monitoring, never a bare "safe".
Interactions documented in the official sources cited on each card. The list covers the medicines represented on this site and is not exhaustive; how the interaction data is compiled.
Azithromycin + Other QT-prolonging medicines (amiodarone, sotalol, some antipsychotics, quinolones, ondansetron)
ModerateMonitoring or dose adjustment advised
Azithromycin with other medicines that prolong the QT interval (amiodarone, sotalol, some antipsychotics and antidepressants, quinolone antibiotics, ondansetron) increases the risk of dangerous heart rhythms.
Why it can occur
QT prolongation
What official information says
US information advises telling a doctor about medicines for irregular heartbeat and other listed drugs, whose doses may need changing or monitoring; the BNF advises caution or avoidance depending on the drug.
What to discuss with a clinician
Official information: an alternative antibiotic where possible; otherwise ECG and electrolyte monitoring.
Azithromycin with citalopram, which also prolongs the QT interval, increases the risk of dangerous heart rhythms.
Why it can occur
QT prolongation
What official information says
US information advises telling a doctor about medicines for irregular heartbeat and other listed drugs, whose doses may need changing or monitoring; the BNF advises caution or avoidance depending on the drug.
What to discuss with a clinician
Official information: an alternative antibiotic where possible; otherwise ECG and electrolyte monitoring.
Therapeutic duplication. Two macrolides together add QT prolongation and gut side effects without benefit. UK
Food and drink
With
Effect
Official advice
Food (capsules)
Food reduces the absorption of azithromycin capsules, so they are taken at least 1 hour before or 2 hours after a meal; tablets and suspension can be taken with or without food. (reduced absorption)
UK information advises taking capsules on an empty stomach and tablets or liquid with or without food. UK
Alcohol
Alcohol does not interact with azithromycin, although it may worsen nausea and stomach upset. (No pharmacological interaction)
UK information states alcohol can be drunk while taking azithromycin. UK
Monitoring
What
Why
Tests and markers
Source
Clinical response
Improvement expected within 48-72 hours; review the diagnosis and organism if not
UK information states azithromycin is not usually recommended in pregnancy unless the benefit outweighs the risk, though there is no strong evidence of harm; it is the treatment of choice for chlamydia in pregnancy, where a doctor will prescribe it. UK
Breastfeeding
UK information states azithromycin can be taken while breastfeeding; small amounts pass into milk and may cause loose stools or thrush in the baby. UK
Children
Licensed from 6 months (oral suspension) at weight-based doses for respiratory, ear, skin and other infections; capsules from 45 kg. UK
Older adults
No dose adjustment, but older people are more likely to have conditions and medicines that prolong the QT interval, and hearing loss with prolonged courses. UK
Kidney impairment
No adjustment for mild to moderate impairment; used with caution when eGFR is below 10, where exposure rises. UK
Liver impairment
Azithromycin is eliminated mainly by the liver; caution in hepatic impairment and avoidance in severe disease, with monitoring for hepatitis. UK
Heart rhythm disorders, long QT and atrial fibrillation on rhythm-control drugs: risk of QT prolongation and torsades; ECG and electrolytes considered, alternatives preferred where possible.
Dosing is intentionally not described: doses depend on the indication, the country's licence, kidney and liver function, age, weight and other medicines, and are set by a prescriber.
Medicines that share the class of Azithromycin. They are separate medicines with their own licences, doses and interactions, not alternative names for Azithromycin.
Medicines often discussed alongside Azithromycin: used together, compared with it, or acting on the same problem by a different route.
Educational content. Anatomy Nexus provides medical education and does not replace professional medical advice, diagnosis, treatment, prescribing or pharmacist review. Doses, choices and monitoring are decided by a prescriber for an individual; never start, stop or change a medicine on the basis of this page.
