Zithromax (Azithromycin): Uses, Side Effects, Dosage

By Terez Malka, MD
Medically reviewed checkmarkMedically reviewed
December 3, 2021

Zithromax is a brand-name form of the antibiotic azithromycin.

Azithromycin is the most commonly prescribed antibiotic in the United States. 

Instead of killing bacteria, Zithromax stops it from growing and multiplying.

The body’s natural defenses can then remove what’s left of the bacteria.

Zithromax is used to treat various types of bacterial infections including respiratory infections, ear infections (when you have an allergy to other antibiotics), and the sexually transmitted infection chlamydia.

Azithromycin has no use in treating viral infections, including COVID-19, common colds, viral bronchitis, or most sinus infections.

In this article, I’ll explain what Zithromax is, talk more about its uses, side effects, and dosages, and provide some precautions for taking the medication.

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What is Zithromax?

Zithromax is a brand name for azithromycin, a prescription drug used to treat a wide variety of bacterial infections.

It works by inhibiting the growth of bacteria.

The medicine cannot be used to treat viral infections such as the common cold or flu.

You should take Zithromax only when it is prescribed by your doctor or a licensed provider.

Antibiotics may not work as well for future bacterial infections if you take them unnecessarily.

Zithromax is not recommended for people with certain heart problems or babies under six months old.

Zithromax Uses

Zithromax treats a range of bacterial infections by preventing the growth of harmful bacteria.


If you are experiencing inflamed tonsils, sore throat, and difficulty swallowing, you may have tonsillitis.

Most cases of tonsillitis are caused by a viral infection, but bacterial infections like strep throat can also cause tonsillitis.

If your tonsillitis is bacterial, your healthcare provider may prescribe you Zithromax if you have allergies to other antibiotics.


Viruses are responsible for approximately 90% of acute bronchitis cases.

It is unlikely that your doctor will treat bronchitis with antibiotics unless you are over 65 years of age, have a chronic lung condition, or at a greater risk of developing pneumonia from your bronchitis.

In this case, Zithromax may be prescribed if you have allergies to other antibiotics.


Pneumonia is an infection that inflames the air sacs of one or both lungs.

They may become full of liquid or pus, making it difficult to breathe. Pneumonia may be caused by bacteria, fungi, or viruses.

Common symptoms of pneumonia include trouble breathing, a wet cough, prolonged dry cough, malaise, fever, and chills.  

If you are diagnosed with “walking” pneumonia or atypical pneumonia, you may be prescribed Zithromax.

Many types of pneumonia will not respond to Zithromax, so you should never start this treatment without evaluation by a doctor or licensed healthcare provider.

Sinus Infection

Sinus infections, also known as sinusitis, are when the cavities within the nasal passages become inflamed.

This can develop from a cold or allergies.

Most sinus infections are viral, so antibiotics will not work to treat them.

If your doctor suspects that you have bacterial sinusitis, they may prescribe you antibiotics.

While Zithromax is not the first-line or preferred treatment for sinusitis, it may be used if you have allergies to other options.

Sexually Transmitted Infections (STIs)

A sexually transmitted infection (STI) occurs from having unprotected sex or sexual contact with an infected person.

If you have tested positive for chlamydia or ureaplasma and do not have symptoms of severe infection or pelvic inflammatory disease, you may be prescribed Zithromax to treat it. 

Zithromax Side Effects

Visit your provider if any of the following common side effects become severe or do not go away:

Potential Severe Side Effects

If you experience any of the following side effects, stop taking the medication immediately.

Contact your healthcare provider or get emergency medical treatment if you experience any of the following:

  • Fast, pounding, or irregular heartbeat
  • Dizziness
  • Fainting
  • Rash with or without a fever
  • Blisters or peeling
  • Fever and pus-filled, blister-like sores, redness, and swelling of the skin
  • Hives or itching
  • Wheezing or difficulty breathing or swallowing
  • Swelling of the face, throat, tongue, lips, eyes, hands, feet, ankles, or lower legs
  • Hoarseness
  • Unusual muscle weakness or difficulty with muscle control
  • Pink and swollen eyes
  • Severe diarrhea (watery or bloody stools) 
  • Yellowing of the skin or eyes
  • Extreme tiredness
  • Unusual bleeding or bruising
  • Lack of energy
  • Loss of appetite
  • Flu-like symptoms
  • Dark-colored urine

If you experience a high fever, facial or throat swelling, difficulty breathing, or uncontrolled vomiting, call 9-1-1 or go to an ER right away. 

How to Take Zithromax

Zithromax should only be taken when it is prescribed to you by your doctor or healthcare provider. 

Dosage and administration

Your dose and length of treatment will be dependent on the type of infection being treated.

Always follow the directions given by your prescriber and what appears on the prescription label of your bottle.

If your Zithromax comes in liquid form, it should be shaken well prior to every dose.

Measure liquid medicine with the dosing syringe provided, or with a special dose-measuring spoon or medicine cup provided by your pharmacist. 

Take your medicine for the full prescribed length of time, regardless of whether you are feeling better.

This will prevent reinfection.

After you have finished your course of antibiotics, throw away any leftover medicine.

Store Zithromax in a cool, dry space at room temperature.

What happens if I miss a dose?

Do not take a double dose.

Take the missed dose as soon as you remember or, if it is close to the time you usually take your next single dose, continue your regular dosing schedule and skip your missed dose. 

What happens if I take too much?

If you or someone else is experiencing a serious allergic reaction to Zithromax, stop taking the medicine.

If you are experiencing serious side effects such as difficulty breathing, a severe skin reaction, or swelling in your face or throat, call 9-1-1 immediately.

You can also seek medical help by calling a poison control center.

For U.S. residents, their local poison control center contact number is 1-800-222-1222.

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Precautions for Zithromax

Before taking Zithromax, discuss your medical history with your doctor or healthcare provider and inform them if you have ever had any of the following medical conditions:

  • Liver disease
  • Kidney disease
  • Myasthenia gravis
  • Low levels of potassium in your blood
  • Irregular heartbeat
  • Long QT syndrome (in you or a family member).

You should not take Zithromax if you are allergic to azithromycin or have experienced jaundice or liver problems as a result of taking Zithromax.

If you are allergic to similar drugs such as clarithromycin, erythromycin, clindamycin, or telithromycin, you should not take Zithromax.

Discuss this with your healthcare provider so they can find the right medical treatment for you.

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Frequently Asked Questions

What is Zithromax used to treat?
Zithromax is used to treat a range of bacterial infections including respiratory infections, sexually transmitted infections, and ear or throat infections in those with allergies to other antibiotics. It is consumed orally or given intravenously. Zithromax works by inhibiting the growth of harmful bacteria.
Is Zithromax used to treat Covid?
No. Zithromax is an antibiotic, which means it is used for the treatment of bacterial infections. COVID-19 is a viral infection, so Zithromax won’t help. Taking Zithromax when you have a viral illness, including COVID-19, will not prevent pneumonia or other complications from developing. Taking antibiotics when they are not needed can cause serious complications and side effects.
What are the side effects of Zithromax?
The most common adverse side effects of Zithromax are diarrhea, abdominal pain, nausea, and vomiting.
How fast does Zithromax work?
You may see improvements in your symptoms as early as the first day. Generally speaking, it takes about five days to work fully.
K Health articles are all written and reviewed by MDs, PhDs, NPs, or PharmDs and are for informational purposes only. This information does not constitute and should not be relied on for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment.

Terez Malka, MD

Dr. Terez Malka is a board-certified pediatrician and emergency medicine physician.

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