All You Need to Know About Azithromycin

By Terez Malka, MD
Medically reviewed checkmarkMedically reviewed
January 18, 2022

Azithromycin is a macrolide antibiotic that is one of the most commonly prescribed antibiotics in the United States.

It treats bacterial infections by stopping the multiplication of bacteria.

Azithromycin does not treat illnesses caused by viruses, like the flu, COVID-19, or common colds. 

In this article, I’ll share everything you need to know about using azithromycin, including what the drug is and how it works, what infections it’s prescribed for, and how to take the medication.

I’ll also list some of the side effects, drug interactions, and risks of azithromycin.

Finally, I’ll tell you when you should see a doctor or healthcare professional.

What is Azithromycin?

Azithromycin is a macrolide antibiotic that treats bacterial infections by stopping bacteria from producing certain proteins.

Without these proteins, the bacteria cannot multiply.

This protein inhibition makes azithromycin effective against many “atypical” bacteria, bacteria that do not respond to other types of antibiotics.

Azithromycin is a prescription drug, which means you cannot legally purchase it without a doctor’s prescription.

It is usually sold as azithromycin, which is its generic name, or as Zithromax, a popular brand name.

It can also be called a Z-pak, when prescribed in a specific dose pack.

The U.S. Food and Drug Administration (FDA) has approved azithromycin to treat infections in both children and adults.

It is available as tablet, capsule, liquid, and injection forms.

Uses for Azithromycin

Azithromycin is used to treat many bacterial infections. These include:

  • Community-acquired pneumonia: Viruses, bacteria, or fungi can cause community-acquired pneumonia. Azithromycin is effective in the treatment of atypical bacterial pneumonia, often known as “walking pneumonia.” It may need to be combined with another antibiotic, and is not generally used for pneumonia in young children or infants. Studies show that it reduces hospital stay and improves outcomes even with a shorter treatment course.

The CDC recommends azithromycin as the first line of treatment for pneumonia caused by Chlamydia pneumoniae. Azithromycin does not work for COVID-19 pneumonia or other viral pneumonias. 

  • Chlamydia: Chlamydia is a sexually transmitted infection (STI). Delayed treatment can lead to pelvic inflammatory disease (PID). The CDC recommends doxycycline but suggests an alternate treatment plan using azithromycin or levofloxacin.
  • Pharyngitis: Most pharyngitis is caused by viruses.  Penicillin is the first choice drug for bacterial pharyngitis, but azithromycin also treats Group A strep pharyngitis, and may be used in those with allergies to other antibiotics.
  • Lyme disease: The CDC recommends that people with early Lyme disease who cannot tolerate doxycycline, cefuroxime, or amoxicillin be treated with azithromycin—although it is less effective than the other three in this case.

Because it is an antibiotic, azithromycin cannot treat viral infections like the flu, COVID-19, or the common cold. 

Using this drug unnecessarily increases the risk of developing antibiotic resistance.

Antibiotic resistance means that the medication may no longer be as effective as the bacteria have developed ways to avoid the antibiotics.

How to Take Azithromycin

Azithromycin can be prescribed in various forms:

  • Injection: This is for patients with severe infections, like community-acquired pneumonia or pelvic inflammatory disease, who need initial intravenous therapy. It will be combined with other antibiotics in most cases.
  • Tablet: Azithromycin tablets are usually taken once daily for 1-5 days. They can be taken with or without food and should always be taken exactly as prescribed. 
  • Liquid: Azithromycin suspensions typically come in a powdered form. These powders are dissolved in varying fluid volumes to achieve different concentrations—the pharmacist will prepare this according to your provider’s instructions. Suspensions are especially useful for pediatric patients and those unable to swallow pills.
  • Extended-release liquid: Extended-release drug forms allow a slow release of the medication into the body for a prolonged period after a single dose. Most patients find them easier to take consistently. This may be used for otitis media and other infections. This is a less-commonly used form of azithromycin and can be toxic in infants.


Azithromycin is available in various strengths:

  • Tablets: Available as 250 mg and 500 mg tablets
  • Oral suspension: Available as 100 mg or 200 mg per 5 mL
  • Extended-release suspension: Available as 2000 mg as a single dose
  • Injection: Available in a 10 mL vial of 500 mg

Your provider will prescribe different azithromycin forms, dosages, and strengths for various infections, depending on the following:

  • Yourt age
  • Condition treated
  • Severity of infection
  • Possible drug interaction
  • Pre-existing health conditions

For example, to treat community-acquired atypical pneumonia or bacterial pharyngitis in adults, most healthcare providers prescribe 500 mg on day 1, and 250 mg per day on days 2-5.

The dosage for various infections is usually written on the patient information leaflet contained in the drug packet.

Your healthcare provider, doctor, or pharmacist can give you further advice.

Antibiotics can take time to work.

On average, doctors prescribe azithromycin for 1-5 days. Other antibiotics take 7-14 days for a full course, depending on the infection being treated. 

Do not take your medication for longer than your doctor prescribed, and make sure to complete your prescribed course even if you start to feel better.

An unfinished medication regimen can lead to antibiotic resistance, making the drug ineffective for future infections.

Side Effects of Azithromycin

Some common side effects of azithromycin include:

Rare, severe side effects include:

For use in children, the most common side effects are:

This is not a complete list of possible side effects. Talk to your doctor immediately if you experience any side effects. 

Azithromycin may be prescribed with caution if you have liver problems since it is eliminated by the liver. 

Azithromycin is also known to worsen symptoms of myasthenia gravis or, in some cases, cause new symptoms. 

If you have a history of torsades de pointes, QT interval prolongation, or bradyarrhythmia, tell your doctor.

Azithromycin can cause or worsen QT prolongation.

Drug Interactions with Azithromycin

Using azithromycin with other drugs can have an impact on its efficacy. In the same way, azithromycin can also affect the effectiveness of other medications.

This effect is known as drug interaction. 

Tell your healthcare provider about any medications you’re currently using.

This includes other prescription medicines, but also non-prescription medicines like vitamins, nutritional supplements, and herbal products.

These are some of the drugs azithromycin reacts with:

  • Antacids containing magnesium hydroxide or aluminum hydroxide
  • Blood thinners like warfarin
  • Gout medication like colchicine
  • Migraine medication like ergotamine
  • Nelfinavir used in the treatment of HIV
  • Amiodarone used for treating irregular heartbeat

Your doctor may change your prescription, dosage or ask you to discontinue using the other drugs for some time if there are possible drug interactions.

They can also choose to watch you closely for possible side effects.

Risks and Warnings Before Taking Azithromycin

Your healthcare provider will only prescribe medications if the benefits far outweigh the risks.

For azithromycin, these are some risks to consider.

Allergic reaction

Most people do not record severe allergic reactions while using azithromycin, but it’s possible. Symptoms include, but are not limited to:

  • Difficulty breathing
  • Hives or other rash
  • Swelling of the face, throat, or tongue 

Do not use azithromycin if you have a medical history of adverse reactions while using azithromycin or similar drugs like erythromycin and clarithromycin.

In the rare case that you notice any signs of a severe allergic reaction, seek emergency medical care or call 9-1-1.

Pregnant or lactating

The FDA classifies azithromycin as a category B drug, meaning they found it safe in reproduction studies using animals.

However, since there are no well-controlled studies in pregnant women, they recommend that pregnant women use azithromycin only when necessary.

Azithromycin can be passed through breastmilk and can cause side effects like diarrhea, rash, and vomiting in a nursing baby.

However, studies show no adverse effect on the baby as the amount of azithromycin in breast milk is less than the standard dose used for treating children. 

If you’re pregnant or breastfeeding, your doctor will decide if azithromycin is the right choice for your infection and condition. 

When to See a Doctor

See your doctor or healthcare provider if you feel unwell and think it might be a bacterial infection.

They will decide on what antibiotic to prescribe based on your test results. 

Remember, you cannot purchase azithromycin over the counter, so you will need a doctor’s prescription to get one. 

Contact your doctor immediately if you experience severe side effects or allergic reactions.

If you do not feel any better after using your medication for the prescribed duration, speak with your doctor or health provider.

Do not discontinue the medicine without your doctor’s approval.

How K Health Can Help

If you’re wondering whether you need azithromycin, it may be time to talk to a doctor.

Did you know you can get affordable primary care with the K Health app? Download K Health to check your symptoms, explore conditions and treatments, and if needed text with a provider in minutes. K Health’s AI-powered app is based on 20 years of clinical data.

Frequently Asked Questions

Do you need to have a certain diet to take azithromycin?
No, you do not need a special diet to take azithromycin. Azithromycin can cause gastrointestinal side effects like nausea and diarrhea. This is because antibiotics typically affect good and bad bacteria in your body. Once your antibiotic regimen is complete, the body will work to restore its balance.
Can azithromycin be used to treat COVID-19?
No. The FDA has not approved azithromycin for the treatment of COVID-19. COVID-19 is a viral illness and antibiotics do not have any effect in treating viruses. A controlled trial showed no significant difference in COVID-19 symptoms when they were prescribed azithromycin. Therefore, azithromycin should only be used to treat bacterial infections as prescribed by your doctor.
Can you overdose on azithromycin?
Yes, you can overdose on azithromycin. This commonly occurs when trying to make up for a skipped dose. If you miss a dose, you can take it when you remember. But if it is close to the next dose, skip it to avoid taking a double dose. An increased level of azithromycin can worsen side effects like diarrhea or irregular heart rhythm. If you have already taken an overdose of azithromycin, contact your healthcare provider, your local poison control center, or call 9-1-1.

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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