Azithromycin Antibiotic: Complete UK Patient Guide
About this guide: This is a comprehensive reference for patients prescribed azithromycin in the UK. It covers all licensed uses, the complete side effect profile, every clinically relevant drug interaction, and specific guidance for special populations including pregnant women, children, and patients with renal or hepatic impairment.
68h
Elimination half-life in tissue — why a single dose can treat a multi-day infection
10+
UK-licensed indications across respiratory, skin, and sexual health conditions
POM
Prescription-only medicine — requires assessment by a registered prescriber
What Is Azithromycin?
Azithromycin is a macrolide antibiotic licensed in the UK for the treatment of a range of bacterial infections. It belongs to the azalide subclass of macrolides—a structural modification that extends its tissue half-life significantly compared to older macrolides such as erythromycin, enabling shorter treatment courses with maintained therapeutic efficacy.
It is available under several brand names in the UK, the most well-known being Zithromax, although generic azithromycin is the form most commonly prescribed. In the United States and some other countries, 5-day azithromycin packs are sometimes referred to as a “Z-Pack.”
Azithromycin is a prescription-only medicine (POM) in the UK. It cannot be purchased over the counter and requires an assessment by a qualified prescriber—whether a GP, specialist, or pharmacist independent prescriber.
How Does Azithromycin Work?
Azithromycin works by binding to the 50S ribosomal subunit of susceptible bacteria, inhibiting the translocation step of protein synthesis. This bacteriostatic mechanism—it slows bacterial growth rather than killing bacteria outright at standard concentrations—is effective because it prevents the bacteria from producing the proteins they need to replicate and survive, allowing the immune system to clear the infection.
Spectrum of Activity
Active against Gram-positive organisms, atypical bacteria (Chlamydia trachomatis, Mycoplasma, Legionella), some Gram-negatives (H. influenzae), and intracellular pathogens. Inactive against most anaerobes and Enterobacteriaceae.
Tissue Penetration
Azithromycin achieves tissue concentrations 10–100 times higher than serum levels, particularly in phagocytes, which transport the drug to sites of infection. This explains its efficacy against intracellular bacteria at doses that produce low serum levels.
Long Half-Life
The tissue elimination half-life of approximately 68 hours means that therapeutic drug levels persist at infection sites for 7–10 days after the final dose. This is what makes single-dose or 3-day courses clinically effective for susceptible infections.
Anti-Inflammatory Effects
Beyond antibacterial activity, azithromycin has immunomodulatory and anti-inflammatory properties. This underlies its off-label use in conditions such as diffuse panbronchiolitis and cystic fibrosis-related lung disease.
All Licensed Uses in the UK
Azithromycin is licensed in the UK by the MHRA for the treatment of the following infections caused by susceptible organisms:
| Infection Category | Specific Indications | Typical Regimen |
|---|---|---|
| Respiratory tract | Community-acquired pneumonia (mild), acute exacerbations of chronic bronchitis, sinusitis, pharyngitis/tonsillitis (where beta-lactam unsuitable) | 500mg once daily for 3 days or 500mg day 1 then 250mg days 2–5 |
| Skin and soft tissue | Uncomplicated skin and skin structure infections (e.g. impetigo, erysipelas) caused by susceptible organisms | 500mg once daily for 3 days |
| Sexually transmitted infections | Urogenital chlamydia (second-line), Mycoplasma genitalium (1st-line, extended regimen), non-specific urethritis (alternative), chlamydia in pregnancy | 1g single dose (chlamydia/NSU); 500mg then 250mg × 4 days (M. genitalium) |
| Ear infections | Acute otitis media in children (where appropriate) | Weight-based paediatric dosing for 3 days |
| Atypical infections | Legionella pneumophila (Legionnaires’ disease), Chlamydophila pneumoniae, Mycoplasma pneumoniae respiratory infections | 500mg once daily for 3–5 days (often combined in severe Legionella) |
Off-label use: Azithromycin is sometimes used off-label in the UK for conditions including Mycobacterium avium complex prophylaxis in HIV, travellers’ diarrhoea, and diffuse panbronchiolitis. These uses are outside the scope of this guide and should be managed under specialist supervision.
Available Forms and Strengths
Azithromycin is available in the UK in several formulations, enabling use across different age groups and clinical situations:
- Capsules—250mg: Commonly prescribed for 3-day respiratory and skin infection courses. Must be taken on an empty stomach (food reduces absorption of capsules by approximately 50%)
- Film-coated tablets—250mg and 500mg: Can be taken with or without food. The 500mg tablet is commonly used for once-daily respiratory courses and the 1g “single-dose” pack (two 500mg tablets) used for chlamydia
- Oral suspension—200mg/5ml: Used in paediatric practice. Can be taken with or without food. Shake well before use and discard any unused suspension after 5 days
- Powder for oral suspension—1g sachet: Dissolve in water; used for single-dose chlamydia treatment where tablets are not available or appropriate
- IV infusion—500mg: For hospitalised patients requiring intravenous administration (e.g. severe community-acquired pneumonia, Legionella). Not available for self-administration
How to Take Azithromycin Correctly
How you take azithromycin depends on the formulation prescribed and the condition being treated. The following general principles apply across most indications:
1
Check your formulation: capsules vs tablets vs suspension
Azithromycin capsules must be taken on an empty stomach—at least 1 hour before or 2 hours after food. Tablets and oral suspension can be taken with or without food. This distinction matters: taking capsules with food can reduce absorption by up to 50%.
2
Take at the same time each day
Consistency helps maintain steady tissue levels throughout the course. For a 3-day or 5-day regimen, choose a time of day you can reliably adhere to and take each dose at approximately the same time.
3
Do not take antacids within 2 hours of azithromycin
Aluminium- and magnesium-containing antacids (e.g. Gaviscon, Maalox, some indigestion remedies) reduce peak azithromycin serum concentrations. Space them at least 2 hours apart. This interaction does not apply to omeprazole or other proton pump inhibitors.
4
Complete the full course
Even for a single-dose chlamydia treatment, the antibiotic remains active in tissues for 7–10 days. For multi-day courses, do not stop early because you feel better—premature discontinuation risks treatment failure and may contribute to resistance.
5
What to do if you miss a dose
Take the missed dose as soon as you remember on the same day. If you do not remember until the next day, skip the missed dose and continue with your regular schedule. Do not double up. For a single-dose treatment, there is no “missed dose”—contact your prescriber if you vomited within 1 hour of taking it.
Side Effects: Common, Uncommon, and Serious
Azithromycin is generally well tolerated. The majority of side effects are mild and gastrointestinal. Serious adverse effects are rare but include cardiac and hepatic reactions that require immediate medical attention.
Common side effects (affecting more than 1 in 100 patients)
- Nausea — the most frequently reported effect; taking tablets or suspension with food reduces this without significantly affecting drug absorption
- Diarrhoea — loose or frequent stools, usually mild and resolving within 1–2 days of completing the course
- Abdominal pain or discomfort — cramping or bloating, typically mild
- Vomiting — less common than nausea; if vomiting occurs within 1 hour of a dose, contact your prescriber about whether a repeat dose is needed
- Headache — reported in a small proportion of patients taking multi-day courses
Uncommon side effects (affecting 1 in 100 to 1 in 1,000 patients)
- Dizziness or vertigo
- Changes in taste or smell (dysgeusia, anosmia) — usually temporary
- Skin rash, photosensitivity — avoid prolonged sun exposure during and for a few days after treatment
- Elevated liver enzymes (usually asymptomatic and transient)
- Oral or vaginal candidiasis (thrush) — antibiotics disrupt normal bacterial flora, allowing Candida overgrowth
- Fatigue or malaise
Serious adverse effects (rare but requiring immediate medical attention)
QT interval prolongation and cardiac arrhythmia: Azithromycin can prolong the cardiac QT interval, predisposing to potentially fatal ventricular arrhythmias including torsades de pointes. This risk is greatest in patients with pre-existing QT prolongation, hypokalaemia, hypomagnesaemia, bradycardia, or those taking other QT-prolonging medicines. Seek immediate medical attention if you develop palpitations, irregular heartbeat, dizziness, or fainting during treatment.
- Severe allergic reaction (anaphylaxis) — symptoms include hives, facial/throat swelling, difficulty breathing, and collapse. Call 999 immediately. Macrolide allergy is a contraindication to azithromycin
- Hepatotoxicity — rare instances of cholestatic jaundice, hepatic necrosis, and hepatic failure have been reported. Seek urgent medical review if you develop jaundice (yellow skin or eyes), dark urine, or severe abdominal pain during or after a course
- Clostridium difficile-associated diarrhoea — all antibiotics carry this risk; severe, persistent, or bloody diarrhoea after completing a course warrants medical assessment
- Stevens–Johnson syndrome / toxic epidermal necrolysis — extremely rare severe skin reactions; seek emergency care for blistering, peeling, or widespread rash with mucosal involvement
Drug Interactions
Azithromycin has a number of clinically important drug interactions. Always inform your prescriber and pharmacist of all medicines you are taking, including over-the-counter preparations and supplements.
| Interacting Medicine | Interaction | Clinical Significance |
|---|---|---|
| Amiodarone, sotalol, quinidine | Additive QT prolongation | High — avoid combination; seek specialist advice |
| Antipsychotics (haloperidol, quetiapine, olanzapine) | Additive QT prolongation | High — discuss with prescriber before azithromycin |
| Fluconazole, itraconazole (azole antifungals) | Additive QT prolongation; may raise azithromycin levels | Moderate–High — use with caution; ECG monitoring may be appropriate |
| Ciclosporin | Azithromycin raises ciclosporin blood levels (inhibits CYP3A4) | Moderate — monitor ciclosporin levels closely |
| Digoxin | Azithromycin may increase digoxin absorption by altering gut flora | Moderate — monitor digoxin levels; toxicity risk |
| Warfarin and other anticoagulants | May potentiate anticoagulant effect; mechanism not fully established | Moderate — monitor INR more frequently during course |
| Ergotamine / dihydroergotamine | Risk of ergotism (vasospasm, ischaemia) | High — avoid concurrent use |
| Aluminium/magnesium antacids | Reduces peak azithromycin serum concentration | Low–Moderate — separate by at least 2 hours |
| Colchicine | Azithromycin may inhibit colchicine transport; risk of toxicity | Moderate — use with caution, particularly in renal or hepatic impairment |
| HIV antiretrovirals (ritonavir, nelfinavir) | May raise azithromycin plasma levels | Low–Moderate — monitor for dose-related adverse effects |
Combined oral contraceptive pill: Azithromycin does not reduce the effectiveness of the combined oral contraceptive pill. Unlike some older antibiotics, macrolides are not known to induce hepatic enzymes that metabolise oestrogen. No additional contraceptive precautions are needed during a short azithromycin course.
Who Cannot Take Azithromycin
Azithromycin is contraindicated or must be used with extreme caution in the following groups. Always disclose your full medical history and current medicines before being prescribed azithromycin.
- Known allergy to azithromycin or any macrolide antibiotic (erythromycin, clarithromycin, roxithromycin). Cross-allergy between macrolides is well documented
- History of azithromycin-associated cholestatic jaundice or hepatic dysfunction
- Severe hepatic impairment (Child-Pugh Class C) — azithromycin is primarily hepatically eliminated; accumulation risk in severe liver disease
- Pre-existing QT prolongation on ECG, or known hereditary long QT syndrome
- Significant bradycardia (resting heart rate persistently below 50 bpm)
- Hypokalaemia or hypomagnesaemia (low potassium or magnesium) — electrolyte disturbances exacerbate QT prolongation risk
- Myasthenia gravis — macrolides may exacerbate neuromuscular blockade, potentially causing respiratory compromise
- Concurrent use of QT-prolonging medicines without specific medical review (see interactions table above)
Special Populations
Azithromycin in Pregnancy
Azithromycin crosses the placenta. It is not classified as a Category A (absolutely safe) drug in pregnancy, as there are no large randomised controlled trials in pregnant women. However, it is listed by BASHH as a recommended option for chlamydia treatment in pregnancy—where it is preferred over doxycycline (absolutely contraindicated) and considered preferable to the longer erythromycin course for many patients.
The decision to use azithromycin in pregnancy should always involve a specialist or GP assessment. Treatment in pregnancy requires a mandatory test of cure at 5–6 weeks post-treatment, and the specific regimen should be agreed with the prescriber managing the pregnancy.
Azithromycin in Breastfeeding
Azithromycin is excreted in breast milk in small amounts. Available evidence does not indicate a significant risk to a breastfed infant from a short maternal course. However, it should be used only when the clinical benefit to the mother justifies the potential risk, and the decision should be discussed with a prescriber.
Azithromycin in Children
Azithromycin is licensed for use in children for certain indications (including acute otitis media and community-acquired pneumonia) and is dosed by weight. The oral suspension formulation (200mg/5ml) is used in paediatric practice. Children under 6 months should not receive azithromycin unless specifically directed by a paediatric specialist.
Azithromycin in Renal Impairment
No dose adjustment is required in mild-to-moderate renal impairment. Azithromycin is predominantly eliminated via bile and faeces rather than urine. In severe renal impairment (eGFR below 10 ml/min/1.73m²), use with caution as limited data are available.
Azithromycin in Hepatic Impairment
Mild-to-moderate hepatic impairment: azithromycin can be used with monitoring. Severe hepatic impairment (Child-Pugh C): azithromycin is contraindicated due to impaired hepatic elimination and risk of accumulation. Liver function should be monitored in patients with known hepatic disease who require a prolonged azithromycin course.
Second-line / pregnancy option
Azithromycin 1g
Single-dose azithromycin for urogenital chlamydia. Suitable when doxycycline is contraindicated or not tolerated.
View treatment →First-line chlamydia (BASHH 2025)
Doxycycline 100mg
First-line for urogenital and rectal chlamydia. 100mg twice daily for 7 days.
View treatment →Need a prescription for azithromycin?
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Start Online AssessmentFrequently Asked Questions about Azithromycin
Can I drink alcohol while taking azithromycin?
There is no direct pharmacokinetic interaction between azithromycin and alcohol. However, both alcohol and azithromycin can cause nausea and gastrointestinal discomfort, and drinking alcohol during an active bacterial infection is generally inadvisable as it may impair immune function and recovery. Moderate alcohol consumption is unlikely to affect treatment efficacy, but heavy drinking should be avoided during any antibiotic course.
Does azithromycin affect the contraceptive pill?
No. Azithromycin does not reduce the effectiveness of combined oral contraceptive pills, progestogen-only pills, or hormonal implants or patches. Unlike enzyme-inducing antibiotics (such as rifampicin), azithromycin does not significantly alter the metabolism of hormonal contraceptives. No additional contraceptive precautions are required during or after a short azithromycin course.
How long does azithromycin stay in your system?
Azithromycin has a serum half-life of approximately 68 hours, meaning it takes roughly 15–17 days to be fully eliminated from the bloodstream. However, tissue concentrations remain therapeutically effective for 7–10 days after the final dose due to its exceptional tissue accumulation. This prolonged activity is the pharmacokinetic basis for single-dose and 3-day treatment regimens.
Can I take ibuprofen or paracetamol with azithromycin?
Yes. There are no clinically significant interactions between azithromycin and standard doses of ibuprofen or paracetamol. Both analgesics can be taken alongside azithromycin if needed for symptom relief during a bacterial infection. Follow the standard dosing instructions for each medicine.
Why has azithromycin been replaced as first-line for chlamydia?
BASHH updated its chlamydia guidelines in 2025, moving doxycycline to first-line following evidence that azithromycin achieves only approximately 83% cure for rectal chlamydia compared to near-complete eradication with a 7-day doxycycline course. Azithromycin remains second-line for urogenital chlamydia and is still the preferred option in pregnancy where doxycycline is absolutely contraindicated.
Can azithromycin cause heart problems?
Azithromycin can prolong the QT interval on an electrocardiogram, which in rare cases may predispose to serious cardiac arrhythmias including torsades de pointes. This risk is highest in patients with pre-existing cardiac conditions, electrolyte disturbances (low potassium or magnesium), or those taking other QT-prolonging medicines. For most healthy adults taking a short course for an STI or respiratory infection, the absolute cardiac risk is very low. Discuss your cardiac history with your prescriber before starting azithromycin.
Is azithromycin the same as erythromycin?
Azithromycin and erythromycin are both macrolide antibiotics and share a similar spectrum of antibacterial activity, but they are not the same drug. Azithromycin is an azalide—a structural modification of erythromycin—with a significantly longer tissue half-life (68 hours vs 1–2 hours), enabling shorter treatment courses. Azithromycin also has fewer gastrointestinal side effects and fewer drug interactions than erythromycin. They are not interchangeable without prescriber guidance, though cross-allergy is possible.
What should I do if I have an allergic reaction to azithromycin?
Stop taking azithromycin immediately. For a mild allergic reaction (skin rash, itching without other symptoms), contact your GP or pharmacist for advice. For a severe allergic reaction—characterised by widespread hives, facial or throat swelling, difficulty breathing, or collapse—call 999 immediately as this constitutes a medical emergency. Inform all future healthcare providers of your macrolide allergy, as cross-reactivity with erythromycin and clarithromycin is possible.
References
- British Association for Sexual Health and HIV (BASHH). UK National Guideline for the Management of Infection with Chlamydia trachomatis. Updated 2025. www.bashh.org/guidelines
- Electronic Medicines Compendium (eMC). Azithromycin 500mg film-coated tablets — Summary of Product Characteristics. www.medicines.org.uk/emc
- BNF. Azithromycin. British National Formulary. 2025. bnf.nice.org.uk
- NICE CKS. Chlamydia — uncomplicated genital. Last revised 2024. cks.nice.org.uk
- MHRA. Azithromycin: updated advice on risk of cardiac side effects. Drug Safety Update. www.gov.uk/drug-safety-update
- Drugs and Lactation Database (LactMed). Azithromycin. National Library of Medicine. nlm.nih.gov
- Kong FYS, Tabrizi SN, Law M, et al. “Azithromycin versus doxycycline for the treatment of genital chlamydia infection: a meta-analysis of randomized controlled trials.” Clin Infect Dis. 2014;59(2):193–205.
- Stockley’s Drug Interactions. Azithromycin interactions. Pharmaceutical Press. 2025.
Medical disclaimer: This article is for informational purposes only and does not constitute medical advice. Azithromycin is a prescription-only medicine (POM). Always consult a qualified healthcare professional before starting, stopping, or altering any antibiotic treatment. Drug interactions and contraindications listed are not exhaustive—always disclose your full medical history and medicine list to your prescriber. In a medical emergency, call 999.