Azithromycin
Pronunciation: az-ith-roh-MY-sin.
- Generic name
- azithromycin
- Brand names
- Zithromax (US, Australia -- TGA ARTG 58797, sponsor Pfizer Australia Pty Ltd, registered 25 February 1997)
- Drug class
- Macrolide (azalide) antibiotic
- Form
- Tablet or oral suspension
- Route
- Oral (tablet or suspension). This page does not cover intravenous azithromycin, a separate hospital-administered product with its own dosing and monitoring.
- Legal status
- Prescription-only medicine
Supply Rules Vary
Trade names by country: United States · United Kingdom · Canada · Australia
Australia: Zithromax (4) · Full directory
What azithromycin is and how it works
Azithromycin is a macrolide antibiotic used to treat a range of bacterial infections, including some respiratory, skin, ear, and sexually transmitted infections. It is also used to prevent certain infections in people with weakened immune systems. (1) (2)
Azithromycin does not work against viral infections such as colds or flu. Taking an antibiotic when it is not needed contributes to antibiotic resistance. Complete the prescribed course as directed even if you feel better.
Mechanism of action: how azithromycin works
Azithromycin acts by binding to the 23S rRNA of the 50S ribosomal subunit of susceptible bacteria, inhibiting bacterial protein synthesis. Its terminal elimination half-life (approximately 68 hours in the reviewed US label) is prolonged due to extensive tissue uptake and subsequent release, which supports short-course or single-dose regimens for some indications. Consult the exact current local label for the specific susceptible-organism list for a given indication. (2) (3)
What azithromycin is used for
Respiratory tract infections
Used for specific bacterial infections such as acute bacterial exacerbation of chronic bronchitis, community-acquired pneumonia, and sinus and throat infections, when caused by susceptible organisms. (2) (3)
Skin and soft-tissue infections
Used for uncomplicated skin infections caused by susceptible bacteria. (2)
Sexually transmitted infections
Used for urethritis and cervicitis caused by susceptible organisms including chlamydia; exact recommended regimens are country- and guideline-specific. (2) (3)
Prevention of Mycobacterium avium complex (MAC) disease
Used in people with advanced HIV infection to prevent MAC disease, usually as a once-weekly regimen decided by the specialist team. (1)
Before taking azithromycin
Do not take / not appropriate for
- Do not take azithromycin if you have had a serious allergic reaction to azithromycin, erythromycin, or another macrolide/ketolide antibiotic. (all products) (3)
Tell your clinician about
- Heart rhythm problems, a family history of long QT syndrome, or low potassium/magnesium levels.
- Liver problems, including any past jaundice or liver injury linked to azithromycin.
- Myasthenia gravis, or any muscle-weakness condition.
- Kidney problems.
- Pregnancy, plans for pregnancy, or breastfeeding.
- Every other medicine used, especially antacids containing aluminium or magnesium, other QT-prolonging medicines, or blood thinners such as warfarin.
How to take azithromycin
- Take azithromycin exactly as prescribed, usually once daily, with or without food, for the number of days directed.
- Swallow tablets whole; shake liquid suspension well before measuring each dose with the device supplied.
- Separate azithromycin from aluminium- or magnesium-containing antacids by at least the interval your pharmacist advises, because they can reduce absorption if taken together.
- Complete the full prescribed course, even if you start to feel better, unless your prescriber tells you to stop.
- MAC-prevention regimens (weekly dosing) are different from short-course infection treatment; follow the specific schedule given for your situation.
Procedures and treatment changes
Tell the treating team before surgery, procedures, or any medicine change. Do not alter treatment without the responsible clinician. (1) (2) (3) (4)
Missed dose
Take the missed dose as soon as you remember. If it is almost time for the next dose, skip the missed dose and continue your regular schedule. Do not take a double or extra dose to make up for a missed one. If you are unsure because your course is very short, contact your pharmacist or prescriber.
Overdose
Contact a poison control center or emergency service, or go to the nearest emergency room. Overdose effects reported are generally similar to, but more intense than, common side effects (nausea, vomiting, diarrhoea); supportive medical care is generally used. (1) (2)
Side effects
Most people tolerate azithromycin well for the short courses typically prescribed. Report new or worsening symptoms, especially diarrhoea that continues after the course, palpitations, or yellowing of the skin or eyes.
Diarrhoea, nausea, abdominal pain, or vomiting
What to notice: Loose stools or stomach upset during treatment.
What to do: Usually mild; tell the prescriber if severe, watery, bloody, or if it continues after finishing the course. (1) (2)
Headache
What to notice: Mild to moderate headache.
What to do: Tell the prescriber if it is severe or persistent. (1)
Persistent or bloody diarrhoea (possible C. difficile-associated colitis)
What to notice: Watery or bloody stools, stomach cramping, or fever, occurring during treatment or up to about two months afterward.
What to do: Contact the prescriber promptly; do not treat with an anti-diarrhoeal medicine without medical advice. (1) (3)
Liver problems
What to notice: Yellowing of the skin or eyes, dark urine, pale stools, severe tiredness, or loss of appetite.
What to do: Contact the prescriber promptly; rare cases of severe, sometimes fatal, liver injury have been reported. (2) (3)
Serious warnings
Heart-rhythm problem (QT prolongation, torsades de pointes) — urgent
Symptoms: Fast, irregular heartbeat, palpitations, dizziness, or fainting.
Action: Seek urgent medical assessment. This risk is higher in people with existing heart-rhythm problems, low potassium or magnesium, or those taking other QT-prolonging medicines; tell every prescriber about your azithromycin course. (2) (3)
Severe allergic reaction (including delayed or recurrent reactions) — emergency
Symptoms: Rash with fever, hives, facial or throat swelling, difficulty breathing, or blistering/peeling skin.
Action: Seek emergency care immediately; a clinician or emergency service will decide whether Azithromycin needs to be stopped. Allergic reactions to azithromycin can recur or worsen even after the medicine is stopped. (1) (2)
Severe liver injury — urgent
Symptoms: Jaundice, dark urine, pale stools, severe fatigue, or right-upper-abdominal pain.
Action: Contact the prescriber urgently for assessment; rare cases of fulminant hepatitis and liver failure have been reported. (3)
C. difficile-associated diarrhoea/colitis — urgent
Symptoms: Severe, watery, or bloody diarrhoea, with or without fever, occurring during or up to about two months after treatment.
Action: Contact the prescriber promptly for assessment. (1) (3)
Worsening of myasthenia gravis or new-onset myasthenic syndrome — urgent
Symptoms: New or worsening muscle weakness, drooping eyelids, or difficulty swallowing/breathing.
Action: Contact the prescriber urgently; people with myasthenia gravis should tell every prescriber before starting azithromycin. (3)
Interactions
| Medicine or test | Effect | Action |
|---|---|---|
| Aluminium- or magnesium-containing antacids | Can reduce azithromycin absorption if taken at the same time. | Separate dosing by the interval advised by the pharmacist; do not change the antibiotic schedule yourself. (1) |
| Other QT-prolonging medicines (e.g. certain antiarrhythmics, antipsychotics, some other antibiotics) | May add to the risk of a serious heart-rhythm problem. | Tell every prescriber about all current medicines; the clinical team will decide whether the combination is appropriate. (2) (3) |
| Warfarin and other anticoagulants | Azithromycin may enhance the effect of warfarin in some patients. | Clotting (INR) monitoring may be needed; do not change your anticoagulant dose without medical advice. (3) |
| Ergot derivatives | Theoretical risk of ergotism when combined with macrolide antibiotics. | Concurrent use is generally avoided; tell the prescriber if you use an ergot-derived medicine. (3) |
Pregnancy, breastfeeding, kidney/liver function, age
Pregnancy
Current information has not established azithromycin is harmful in pregnancy, but it should be used only when a clinician judges it clinically necessary. Discuss your situation with the prescriber. (2) (3)
Breastfeeding
Azithromycin passes into breast milk; it has been detected in breast milk samples for up to 4 weeks after a dose. Watch a breastfed infant for diarrhoea, vomiting, or rash, and tell the prescriber about breastfeeding before starting treatment. (2) (3)
Infants under 6 weeks old
Watch for vomiting, irritability, or feeding problems, which may suggest a rare narrowing of the stomach outlet (pyloric stenosis) linked to macrolide antibiotics in early infancy; contact the paediatric team if these occur. (1)
Heart, liver, or kidney disease; myasthenia gravis
These conditions can change the risk of serious side effects. The prescriber must weigh the exact clinical situation against the current local product information rather than a general rule. (3)
Monitoring
Before starting
- Confirm the infection is likely bacterial and consider culture/sensitivity where relevant.
- Review cardiac history, QT-risk factors, electrolytes, liver history, myasthenia gravis status, and current medicines.
During treatment
- Watch for diarrhoea, palpitations, jaundice, muscle weakness, or allergic symptoms.
- Consider ECG or electrolyte monitoring in patients with recognised QT-risk factors, per clinical judgement.
- Assess response and completion of the prescribed course.
Storage
Store tablets at room temperature in the original container, tightly closed, away from excess heat and moisture, out of sight and reach of children. Discard any unused liquid suspension after finishing the course, per the pharmacist's instructions.
Study the drug class: Macrolides
Professional information
Clinician-facing context only. Use the current local product label and antimicrobial-stewardship guidance for exact indication-specific regimens.
United States / United Kingdom (oral tablet labels)
Indication: Typical short-course bacterial infection
Dose summary: Regimens are indication-specific (e.g. a 3-day once-daily course, or a day-1 loading dose followed by a lower once-daily dose for 4 more days, per the UK SmPC; other regimens including single-dose therapy apply to specific indications). No universal regimen is displayed here; confirm the exact current dose and duration against the local label and guideline.
Renal context: The reviewed US label states that dose adjustments were not made in its clinical studies, but notes increased azithromycin levels in severe renal impairment (GFR less than 10 mL/min); it does not give an explicit adjustment recommendation for mild-to-moderate impairment. Consult the exact current local label for renal dosing guidance. (2) (3)
Hepatic guidance
Use with caution in hepatic impairment; the prescriber will decide whether to discontinue treatment promptly if signs of hepatitis develop. Use the exact current local label rather than a general rule.
Overdose note
The reviewed US label describes overdose management as general symptomatic and supportive measures; it does not specify cardiac monitoring for overdose. Given the separate QT-prolongation warning for therapeutic use, clinicians may still choose cardiac monitoring at their own judgement. (2) (3)
Frequently asked questions
Can azithromycin treat a cold or the flu?
No. Azithromycin is an antibiotic and does not work against viral infections such as colds or flu. (1) (2)
Why does azithromycin carry a heart-rhythm warning?
Azithromycin can prolong the QT interval and, rarely, trigger a dangerous heart rhythm (torsades de pointes), particularly in people with existing heart-rhythm risk factors or those taking other QT-affecting medicines. (2) (3)
Should I stop azithromycin as soon as I feel better?
No, unless your prescriber tells you to. Completing the full prescribed course helps clear the infection and reduces the risk of antibiotic resistance. (1)
What is the mechanism of action of azithromycin?
Azithromycin acts by binding to the 23S rRNA of the 50S ribosomal subunit of susceptible bacteria, inhibiting bacterial protein synthesis. Its terminal elimination half-life (approximately 68 hours in the reviewed US label) is prolonged due to extensive tissue uptake and subsequent release, which supports short-course or single-dose regimens for some indications. Consult the exact current local label for the specific susceptible-organism list for a given indication. (2) (3)
References
- Azithromycin: MedlinePlus Drug InformationMedlinePlus, U.S. National Library of Medicine · United States · accessed 2026-07-26 · source 1
- ZITHROMAX (azithromycin dihydrate) tablet, film coated — prescribing information, revised 2024-08-02U.S. National Library of Medicine DailyMed / FDA-sourced label · United States · accessed 2026-07-26 · source 2
- Azithromycin 250 mg film-coated tablets — Summary of Product Characteristics (Milpharm Limited/Aurobindo Pharma)electronic Medicines Compendium (UK) · United Kingdom · accessed 2026-07-23 · source 3
- ZITHROMAX azithromycin 500mg (as dihydrate) tablet blister pack — ARTG entry 58797Therapeutic Goods Administration (TGA), Australia · Australia · accessed 2026-07-26 · source 4
Brand names by country
Single-ingredient azithromycin names are shown separately by country. Product availability, strengths, and supply rules can change; combination products are not included here.
Priority countries
United States
- Zithromax250 mg, 500 mg/5mL, 200 mg/5mL, 500 mg · pfizer laboratories div pfizer inc
- AZASITE10 mg/mL · thea pharma inc.
United Kingdom
- Azithromycin (generic; Milpharm/Aurobindo) (3)current licensed product · 250 mg · Milpharm Limited (Aurobindo Pharma), Ruislip, UK
Canada
- ZITHROMAX
- ZITHROMAX - PWS ORL
- ZITHROMAX FOR INTRAVENOUS
- PRO-AZITHROMYCINE
- APO-AZITHROMYCIN Z
Australia
- Zithromax (4)current register product lower confidence source · 500 mg · Pfizer Australia Pty Ltd · Source verification is search-result-confirmed, not a live-opened TGA page (direct fetch timed out twice); re-verify with a live fetch before publication.