What to Know About Azithromycin (Zithromax Z-Pack)

A Common Antibiotic for Treating Bacterial Infections

Azithromycin is a versatile antibiotic used to treat a wide variety of bacterial infections, including those affecting the lungs, skin, and gastrointestinal system, as well as a number of sexually transmitted infections (STIs). It belongs to a class of medications called macrolide antibiotics and is derived from a similarly named antibiotic, erythromycin. It works by interfering with a bacterium's ability to produce proteins, thus inhibiting growth. Azithromycin is available as a tablet or liquid to be taken orally, an injectable solution, and eye drops.

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Brand names of azithromycin include Zithromax, Zithromax Single Dose Packets, Zithromax Tri-Paks, Zithromax Z-Paks, and Zmax (an extended-release formulation).


Azithromycin is used to treat and prevent many different types of infections. They include:

Azithromycin also is used prophylactically to prevent heart infection in people having dental or other procedures and to prevent STIs in victims of sexual assault.

Azithromycin is often prescribed as an alternative to penicillin for people who are allergic to it.

Off-Label Uses

Some doctors prescribe the antibiotic to treat moderate to severe acne. It is also sometimes administered to children in intensive care. Azithromycin also has been investigated in combination with hydroxychloroquine to treat COVID-19.

Before Taking

A doctor may prescribe azithromycin if you exhibit signs of an infection, which vary widely depending on where the infection occurs. Fever, chills, fatigue, are general infection symptoms but so is pain at the site of infection. Azithromycin is the generic form of the drug but brand names include Zithromax, Azasite, Z-pack and Zmax, the extended release form of the drug. Both the generic and brand name forms are often prescribed in three or five-day "packs." Zithromax, and azithromycin in general, comes in several dosages and forms, including oral tablets and liquids for oral use, injections and intravenous drips.

Let your doctor know if you have ever had an allergic reaction to azithromycin and what medications, vitamins and supplements you currently take, if any. While some drugs pose minor interaction risks, others may contraindicate use.

Precautions and Contraindications

Azithromycin is strongly contraindicated in certain circumstances. If any apply to you and a doctor who isn't familiar with your medical history wants to prescribe azithromycin for you, tell them so they can give you a safer alternative. The contraindications for azithromycin are:

  • Liver disease or a history of liver problems after taking azithromycin
  • Long QT Interval Syndrome, a genetic condition affecting heart rhythm. In people with this condition, taking azithromycin has been associated with cardiac arrhythmias and a dangerous arrhythmia called ventricular tachycardia resulting in sudden death.
  • Low blood levels of magnesium or potassium
  • A blood infection, heart failure, cystic fibrosis, myasthenia gravis (a condition of muscles and the nerves that control them), or kidney disease
  • Pregnancy. If you're actively trying to conceive or are breastfeeding, tell your doctor before you take azithromycin. If you become pregnant while taking azithromycin, call your doctor.

Because azithromycin is so widely used, people are now developing antibiotic resistance, and the drug has become less effective against certain infections, including community-acquired pneumonia, ear infections, acute sinusitis and MRSA, a superbug with broad antibacterial resistance.

Other Drug Class Names

Azithromycin is classified as a macrolide antibiotic. Other drugs belonging to this class include:

  • Erythromycin
  • Biaxin (clarithromycin)
  • Dificid (fidaxomicin)
  • Ketek (telithromycin)


Typically, azithromycin is taken once a day, with or without food, for three to 10 days, depending on the type of infection being treated. A common dose is 500 milligrams (mg) in a single dose on day one, which might come as a pill, a liquid, or a dry powder to which water must be added, followed by 250 mg orally once a day on days 2 to 5.

All listed dosages are according to the drug manufacturer. Check your prescription and talk to your doctor to make sure you are taking the right dose for you.

How to Take and Store

The extended-release suspension Zmax is usually taken on an empty stomach (at least one hour before or hours after a meal) as a one-time dose. Use the azithromycin extended-release suspension within 12 hours of receiving it from the pharmacy or after adding water to the powder. Take the medication following the indications on the label, and as directed by your doctor or pharmacist. Do not take more or less than what has been prescribed.

Take azithromycin until you finish the prescription, even if you feel better. If you stop taking azithromycin too soon or skip doses, your infection may return, allowing the bacteria to become resistant to antibiotics.

As with all medications, store in a cool, dry place, out of sight and out of reach of children.

Side Effects

As with any medication, azithromycin can cause side effects. Many of those side effects are related to the digestive system, but most are mild and should pass after your course of treatment is finished.


  • Nausea
  • Diarrhea
  • Vomiting
  • Stomach pain
  • Headache


Immediately stop taking the medication and seek medical attention if you experience the following:

  • Fast, pounding, or irregular heartbeat
  • Feeling faint or dizzy
  • Itching, hives, rash, or peeling
  • Fever and pus-filled, blister-like sores
  • Yellow, or pink and swollen eyes
  • Wheezing or difficulty breathing or swallowing
  • Swelling of the face, throat, tongue, lips, eyes, hands, feet, ankles, lower legs, or skin
  • Severe diarrhea (watery or bloody stools) and stomach cramps occurring up to two months or more after treatment
  • Extreme fatigue or lack of energy
  • Unusual bleeding or bruising
  • Loss of appetite
  • Pain in the upper right part of the abdomen
  • Flu-like symptoms
  • Dark-colored urine
  • Unusual muscle weakness or difficulty with muscle control

Warnings and Interactions

Although azithromycin is widely used and is a common substitute for patients with allergies to other antibiotics, there are things to watch out for:

  • Some people may be allergic. Tell your doctor if you have previously had an allergic reaction to another macrolide antibiotic or to inactive ingredients in tablets or liquid suspensions (such as dyes or preservatives).
  • Do not take the drug simultaneously with antacids containing aluminum hydroxide or magnesium hydroxide such as Maalox, Mylanta or Tums. Ask your doctor or pharmacist how many hours before or after you take azithromycin you may take these medications. The extended-release suspension may be taken at any time with antacids.
  • Certain blood thinners and drugs taken for irregular heartbeat can cause drug interactions. Your doctor may need to change the doses of your medications or monitor you carefully for side effects if you take Coumadin, Jantoven (warfarin); Colcrys, Gloperba (colchicine); Neoral, Sandimmune (cyclosporine); Lanoxin (digoxin); D.H.E. 45, Migranal (dihydroergotamine); Ergomar (ergotamine); Cordarone, Pacerone (amiodarone); Tikosyn (dofetilide): Procanbid (procainamide); Betapace, Sorine, (quinidine, and sotalol); Viracept (nelfinavir); Dilantin (phenytoin); and terfenadine (not available in the U.S.).
  • Drinking alcohol while taking this antibiotic may increase side effects.
  • Talk to your doctor about all medications, supplements, and vitamins that you currently take. While some drugs pose minor interaction risks, others may outright contraindicate use or prompt careful consideration as to whether the pros of treatment outweigh the cons in your case.
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Article Sources
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  1. MedlinePlus. Azithromycin. Apr 15, 2020.

  2. Oshikoya KA, Wharton GT, Avant D, et al. Serious adverse events associated with off-label use of azithromycin or fentanyl in children in intensive care units: A retrospective chart review. Paediatr Drugs. 2019;21(1):47-58. doi:10.1007/s40272-018-0318-9

  3. Gbinigie K, Frie K. Should azithromycin be used to treat COVID-19? A rapid review. BJGP Open. 2020;4(2). doi:10.3399/bjgpopen20X101094

  4. Rao GA, Mann JR, Shoaibi A, et al. Azithromycin and levofloxacin use and increased risk of cardiac arrhythmia and deathAnn Family Med. 2014;12(2):121-127. doi:10.1370/afm.1601

Additional Reading
  • Schwartz PJ, Woosley RL. Predicting the Unpredictable: Drug-Induced QT Prolongation and Torsades de Pointes. J Am Coll Cardiol 2016; 67:1639.

  • Voelker R. Another Caution for Clarithromycin. JAMA 2018; 319:1314.

  • Ray WA, Murray KT, Hall K, et al. Azithromycin and the Risk of Cardiovascular Death. N Engl J Med 2012; 366:1881.
  • US Food and Drug Administration. Azithromycin (Zithromax or Zmax): Drug Safety Communication - Risk of Potentially Fatal Heart Rhythms. http://www.fda.gov/Safety/MedWatch/SafetyInformation/SafetyAlertsforHumanMedicalProducts/ucm343350.htm?source=govdelivery