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Azithromycin: 7 things you should know

Medically reviewed by Carmen Fookes, BPharm. Last updated on Aug 17, 2022.

1. How it works

  • Azithromycin may be used to treat infections caused by susceptible bacteria.
  • Azithromycin works by binding to the 23S rRNA of the 50S ribosomal subunit of susceptible bacteria such as Mycobacterium avium, M. intracellulare, and Chlamydia trachomatis. This inhibits bacterial protein synthesis and kills bacteria.
  • Azithromycin belongs to the class of medicines known as macrolide antibiotics.

2. Upsides

  • Used to treat mild-to-moderate infections caused by susceptible bacteria occurring on the skin, in the lungs, in the ears, and some infections that have been sexually transmitted.
  • Used specifically for the treatment and prevention of mycobacterium avium complex (a type of respiratory infection) in people with advanced HIV. May be used in addition to other antibiotics.
  • Active against a wide range of microorganisms and shows good penetration into human tissue. Some bacteria may be resistant (not killed by azithromycin).
  • May be better tolerated and have more effective tissue penetration than other similar antibiotics such as erythromycin.
  • May be used to treat bacterial infections in people intolerant of penicillins.
  • Can be dosed once daily which improves adherence.
  • Available as a tablet or capsule, in an extended-release form, as a powder for reconstitution, and in an injectable form.
  • Generic azithromycin is available.

3. Downsides

If you are between the ages of 18 and 60, take no other medication or have no other medical conditions, side effects you are more likely to experience include:

  • Nausea, diarrhea, vomiting, abdominal pain, dyspepsia, flatulence, fatigue, headache are some of the more common side effects.
  • Liver damage and may affect liver function, sometimes fatally. Must be discontinued if any signs of liver dysfunction occur.
  • May cause changes in the way the heart beats, resulting in the development of cardiac arrhythmias. The risk is greater in people with a history of QT prolongation, on other drugs known to prolong the QT interval, with low levels of potassium or magnesium in their blood, and in those receiving anti-arrhythmic agents such as sotalol, amiodarone, and procainamide.
  • Has been associated with a two-fold increase in the rate of cardiovascular death in adults relative to amoxicillin. This risk was greatest during the first five days of azithromycin use and is independent of preexisting cardiovascular disease.
  • Severe diarrhea associated with Clostridium difficile is a potential side effect of almost all antibacterial agents, including azithromycin.
  • May cause severe skin reactions and photosensitivity (increased sensitivity to sunlight). Discontinue azithromycin and seek urgent medical advice should a rash develop. Has also been associated with severe allergic reactions.
  • May interact with several other medications, including warfarin and nelfinavir (see interactions below).
  • Dosage may need decreasing in those with renal disease and may not be suitable for people with myasthenia gravis. Use in neonates has been associated with infantile hypertrophic pyloric stenosis (IHPS). May not be effective as the sole therapy for treating gonorrhea or syphilis.
  • Has not been associated with an increased risk of birth defects when used to treat bacterial infections in pregnant women. Weigh up the risks versus benefits before administering to pregnant women. Azithromycin has been detected in human milk and the infant should be monitored for diarrhea, vomiting, or a rash if it is decided to continue with breastfeeding while being administered azithromycin.

Note: In general, seniors or children, people with certain medical conditions (such as liver or kidney problems, heart disease, diabetes, seizures) or people who take other medications are more at risk of developing a wider range of side effects. View complete list of side effects

4. Bottom Line

  • Azithromycin is an antibiotic used to treat a variety of different infections. It has the distinct advantage of once-daily dosing; however, diarrhea is a common side effect.

5. Tips

  • May be taken with or without food; however, azithromycin may be better tolerated if taken with food.
  • Do not take aluminum or magnesium-containing antacids two hours before or two hours after you take azithromycin because antacids can make azithromycin less effective.
  • Discontinue azithromycin immediately and seek urgent medical advice if any sign of an allergic reaction (such as a rash or difficulty breathing) occurs.
  • Take exactly as directed and finish the course as prescribed by your doctor, even if you feel better beforehand. Skipping doses or not completing treatment can decrease the effectiveness of the treatment and promote the development of resistance.
  • Although diarrhea is common with azithromycin, contact your doctor if you develop severe diarrhea especially if it is very watery or contains blood. Sometimes diarrhea may occur one to two months after starting azithromycin.
  • Contact your doctor immediately if you develop any signs of liver disease such as yellowing of the skin or whites of the eyes, upper right abdominal pain, rash, clay-colored stools, severe nausea, and vomiting.
  • If you are allergic to other macrolides (such as clarithromycin, erythromycin, or telithromycin) do not take azithromycin. Also, avoid azithromycin if you have taken it before and it caused damage to your liver.
  • Take azithromycin Zmax extended-release liquid at least one hour before or two hours after a meal. Throw away any mixed Zmax suspension that has not been used within 12 hours.
  • Avoid excessive exposure to sunlight or tanning beds. Use an SPF 30 or higher sunblock when outside and wear protective clothing as azithromycin can make you sunburn more easily.
  • Tell your doctor if you are pregnant or breastfeeding before taking azithromycin.

6. Response and effectiveness

  • It takes between two and a half to just over three hours for peak concentrations of azithromycin to be reached. A loading dose (a higher than normal starting dose) may be used to reach steady concentrations sooner.
  • Can be dosed once daily.
  • May take several days before symptoms of infection start to abate. Always finish the course as prescribed.
  • Resistance to azithromycin has been reported, mainly through modification of the 23S rRNA target, most often by methylation. Ribosomal modifications can determine cross-resistance to other macrolides, lincosamides, and streptogramin B (MLS B phenotype).

7. Interactions

Medicines that interact with azithromycin may either decrease its effect, affect how long it works for, increase side effects, or have less of an effect when taken with azithromycin. An interaction between two medications does not always mean that you must stop taking one of the medications; however, sometimes it does. Speak to your doctor about how drug interactions should be managed.

Common medications that may interact with azithromycin include:

  • amiodarone
  • apixaban
  • aspirin
  • BCG live (Theracrys)
  • dabigatran
  • dalteparin
  • digoxin
  • dronedarone
  • live typhoid vaccine
  • mifepristone
  • NSAIDs, such as ibuprofen, diclofenac, and naproxen
  • pimozide
  • quinidine.

In general, any medicine that can increase the risk of bleeding (such as clopidogrel, SSRI antidepressants, fish oils) may interact with azithromycin. Alcohol may increase the side effects of azithromycin and there is the potential for grapefruit products to interact with azithromycin; however, reports are uncommon.

Note that this list is not all-inclusive and includes only common medications that may interact with azithromycin. You should refer to the prescribing information for azithromycin for a complete list of interactions.


Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use azithromycin only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Copyright 1996-2023 Revision date: August 17, 2022.