What Is Zithromax (Azithromycin)?

An Antibiotic That Can Treat Many Different Infections

Zithromax is a versatile antibiotic that is commonly used for treating many types of bacterial infections. This may include skin infections, ear infections, respiratory infections, and sexually transmitted infections. It is available as a pill, powder, liquid, or injection.

Is erythromycin the same as azithromycin?

No, these are different antibiotics. However, Zithromax (azithromycin) is derived from erythromycin and they are both in a class of antibiotics called macrolides.

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What Is Zithromax Used For?

Infections that can be treated with Zithromax include:

  • Respiratory tract infections
  • Skin and other soft-tissue infections
  • Acute bacterial exacerbations of an inflammatory lung condition called chronic obstructive pulmonary disease (COPD)
  • Otitis media, or middle ear infection
  • Community-acquired pneumonia
  • Bacterial conjunctivitis, or eye infection
  • Mycobacterium avium complex or MAC, which is an opportunistic respiratory infection
  • Chancroid, a sexually transmitted infection (STI) that can cause genital ulcers
  • Pharyngitis, or throat inflammation
  • Tonsillitis, or tonsil inflammation
  • Chlamydial cervicitis, or inflammation of the cervix due to chlamydia
  • Urethritis, or inflammation of the urethra that may be due to an STI

It should be noted that high levels of antibiotic resistance make Zithromax a poor choice for treating certain infections like community-acquired pneumonia and acute sinusitis.

Of particular note, Zithromax is ineffective in combating infections caused by MRSA, a superbug with broad antibacterial resistance.

Mechanism of Action

How Zithromax is processed in the body allows it to interact with fewer drugs when compared to erythromycin, which has a drug-drug interaction with some statins (e.g., Zocor or Crestor).

Like the other macrolides—erythromycin and clarithromycin—Zithromax works by binding to the bacteria 50S ribosomal subunit, thus interfering with the bacteria's ability to produce proteins. Bacteria need to produce proteins to survive. Depending on the organism and the drug concentration, macrolides can either stop bacterial growth or kill bacteria.

How long does Zithromax take to start working?

How long Zithromax takes to work can vary. For example, it can take up to seven days for Zithromax to treat chlamydia.

Zithromax Dosage

Dosage will vary depending on the route of administration and what infection the medication is treating. Zithromax is available in tablets, oral suspensions, injections, and eye solutions.

Dosage examples for adults:

  • For skin infections or tonsillitis: one 500 milligram (mg) tablet of Zithromax once for the first day of treatment, followed by one 250 mg tablet on days two through five
  • For acute bacterial exacerbation of COPD: one 500 mg tablet once daily for three days
  • For chancroid: a one time dose of 1 gram of Zithromax

Always follow your healthcare provider's instructions, as the type of infection you have will dictate the Zithromax dosage needed for treatment.

Adverse Effects

Although not as severe as erythromycin, azithromycin can also cause gastrointestinal distress like nausea or vomiting.

These unwanted side effects can be mitigated by eating some food before you take an oral dose of azithromycin.

A Word From Verywell

If you or a loved one has heart disease, it may be a good idea to avoid azithromycin. This drug is known to cause heart rhythm related issues and an increased risk of heart-related death.

If prescribed Zithromax for an infection, be sure to complete your full course of treatment. If you don't complete treatment, resistant bacteria can survive, spread, and infect others.

6 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. U.S. Food and Drug Administration. Zithromax Label.

  2. Fair RJ, Tor Y. Antibiotics and bacterial resistance in the 21st centuryPerspect Medicin Chem. 2014;6:25–64. Published 2014 Aug 28. doi:10.4137/PMC.S14459

  3. Fohner AE, Sparreboom A, Altman RB, Klein TE. PharmGKB summary: Macrolide antibiotic pathway, pharmacokinetics/pharmacodynamicsPharmacogenet Genomics. 2017;27(4):164-167. doi:10.1097/FPC.0000000000000270

  4. Wisconsin Department of Health Services. Chlamydia treatment information sheet.

  5. Pfizer Medical Information. Zithromax tablet, suspension dosage and administration.

  6. Juurlink DN. The cardiovascular safety of azithromycinCMAJ. 2014;186(15):1127–1128. doi:10.1503/cmaj.140572

Additional Reading
  • Mosby's Drug Reference for Health Professionals, Second Edition published by Elsevier in 2010.
  • Deck DH, Winston LG. Chapter 44. Tetracyclines, Macrolides, Clindamycin, Chloramphenicol, Streptogramins, & Oxazolidinones. In: Katzung BG, Masters SB, Trevor AJ. eds. Basic & Clinical Pharmacology, 12e. New York, NY: McGraw-Hill; 2012.
  • O'Donnell MR, Saukkonen JJ. Chapter 168. Antimycobacterial Agents. In: Longo DL, Fauci AS, Kasper DL, Hauser SL, Jameson J, Loscalzo J. eds. Harrison's Principles of Internal Medicine, 18e. New York, NY: McGraw-Hill; 2012.

By Naveed Saleh, MD, MS
Naveed Saleh, MD, MS, is a medical writer and editor covering new treatments and trending health news.