Azithromycin (Zithromax) is an antibiotic that can help treat certain bacterial infections. It is generally safe to use while breastfeeding, but people with existing heart conditions should avoid this drug.

Azithromycin is an antibiotic in the macrolides class. The Food and Drug Administration (FDA) first approved azithromycin in 1991.

Like all antibiotics, azithromycin can only fight certain bacteria. For this reason, it is important to talk to a doctor before taking the drug. It is not effective against viral infections or as a pain reliever.

This article provides an overview of azithromycin, including its uses, side effects, warnings, and drug interactions.

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A doctor may prescribe azithromycin for a sinus infection, COPD complications, or tonsillitis, for example.

Azithromycin can fight a wide range of bacteria, including many in the Streptococcus family. It can stop harmful bacteria from growing.

Healthcare providers tend to use this drug to treat mild-to-moderate infections of the lungs, sinuses, skin, and other body parts.

A doctor may prescribe azithromycin to treat the following bacterial infections:

  • sinus infections related to Moraxella catarrhalis or Streptococcus pneumoniae
  • community-acquired pneumonia related to Chlamydia pneumoniae, Haemophilus influenzae, or S. pneumoniae
  • chronic obstructive pulmonary disease (COPD) complications related to M. catarrhalis or S. pneumoniae
  • some skin infections related to Staphylococcus aureus, Streptococcus pyogenes, or Streptococcus agalactiae
  • tonsillitis related to S. pyogenes
  • urethritis and cervicitis related to Chlamydia trachomatis
  • chancroid genital ulcers (in males) related to Haemophilus ducreyi
  • certain ear infections in children aged 6 months and over, such as those related to M. catarrhalis

Azithromycin is a prescription medication. Therefore, people should not take it without a prescription.

The drug is available in the form of a tablet, an oral suspension solution, an eye drop, and an injection. The best type and dosage depends on the infection a person has.

People can take the drug with or without food. They should thoroughly shake the liquid form before use.

Some examples of common dosages include:

community-acquired pneumonia
skin infections
an initial dose of 500 milligrams (mg) followed by 250 mg once daily until day 5
mild-to-moderate bacterial COPD exacerbations500 mg per day for 3 days
an initial dose of 500 mg followed by 250 mg once daily until day 5
sinus infections500 mg per day for 3 days
chancroid genital ulcersa single dose of 1 gram (g)
a single dose of 1 g
gonococcal urethritis
a single dose of 2 g

Using antibiotics incorrectly can lead to the development of drug-resistant strains of bacteria, meaning that antibiotics no longer work against them. This is called antibiotic resistance.

When taking azithromycin or any other antibiotic, people should heed the following precautions:

  • Take the entire course of antibiotics the doctor recommends, even when starting to feel better.
  • Do not take antibiotics without a prescription. Not all antibiotics can treat all bacteria.
  • Do not share antibiotics.
  • Do not take antibiotics on a different dosing schedule than the one a doctor prescribes.
  • Immediately call a doctor if side effects develop.
  • Go to the emergency room for symptoms of an allergic reaction, such as trouble breathing.

Learn more about antibiotic resistance here.

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Side effects of azithromycin may include nausea and vomiting.

Like all drugs, azithromycin can have certain side effects. These are usually minor. In clinical trials, only 0.7% of people stopped taking Zithromax because of its side effects.

Most of the side effects that led people to stop taking the drug were gastrointestinal, such as:

  • nausea
  • vomiting
  • diarrhea
  • pain in the abdomen

Less common side effects, occurring in up to 1% of cases, include:

Serious side effects are rare but can include:

  • liver damage, especially in people with a history of liver health problems
  • heart rhythm changes, which are more likely in people who take heart rhythm medications, older people, and those with low blood potassium
  • serious allergic reactions

People who have myasthenia gravis, a condition that causes muscle weakness, may develop worsening symptoms or breathing problems.

People with a history of allergic reactions to macrolides or ketolides should not take azithromycin.

Doctors should not prescribe this drug to treat pneumonia if a person:

  • has cystic fibrosis
  • has a hospital-acquired infection
  • has bacteremia
  • requires a stay in the hospital
  • is older or debilitated
  • has a significant underlying health problem, such as immune system problems

People should not rely on azithromycin to treat syphilis.

A person should speak to a doctor about any existing heart, kidney, and liver conditions before taking azithromycin, including an irregular heartbeat and especially QT prolongation.

What does the research say?

A large 2012 cohort study found a small increase in the risk of cardiovascular death among people taking azithromycin. The risk was higher among those with other risk factors for heart disease, such as smoking, low physical activity levels, and a high body mass index (BMI).

The study reported that when compared with amoxicillin, there were 47 additional cardiovascular deaths per 1 million azithromycin prescriptions. Among people with the highest risk of heart disease, there were 245 more deaths per 1 million courses of azithromycin.

This suggests that other antibiotics, such as amoxicillin, may be a safer option for people with heart disease or certain types of heart arrythmias.

In 2018, the FDA issued a warning about the long term use of azithromycin in people with certain blood or lymph node cancers who have stem cell transplants. Emerging research has suggested that azithromycin may increase the risk of cancer relapse in these people.

Following a stem cell transplant, some people take azithromycin to reduce the risk of an inflammatory lung condition called bronchiolitis obliterans syndrome. The FDA have not approved azithromycin for this use, however.

Rarely, azithromycin can cause liver toxicity. People should stop taking the drug and call their doctor if they develop any symptoms of liver problems, including dark urine, itching, or yellow eyes.

In newborns younger than 42 days old, azithromycin may cause a dangerous condition called infantile hypertrophic pyloric stenosis. Caregivers should contact a doctor if a baby becomes irritable or vomits when eating.

Azithromycin may interact with other medications a person is taking.

For example, using azithromycin while taking nelfinavir, which is a drug that helps treat HIV, can increase the risk of liver abnormalities and hearing problems.

Azithromycin can also increase the effects of blood thinners such as warfarin.

Other drugs that may interact with azithromycin include:

  • digoxin, a heart medication
  • colchicine, a gout medication
  • phenytoin, a seizure medication
  • antacids that contain magnesium or aluminum

A person should tell a doctor about all current medications, supplements, and remedies before taking azithromycin. Always speak to a doctor before stopping taking medications.

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A person may take azithromycin while breastfeeding but should discuss it with a healthcare professional first.

Azithromycin may be safe to use during pregnancy and while breastfeeding.

Studies of animals who received very large doses of azithromycin did not find an increased risk of miscarriage or birth defects.

However, there have been no high quality studies in pregnant humans, so the drug label currently states that “azithromycin should be used during pregnancy only if clearly needed.”

Azithromycin can transfer into breast milk and may remain present for 48 hours following a person’s last dose. Although it is generally safe to use when breastfeeding, azithromycin may cause diarrhea, vomiting, or a rash in some babies.

A person should tell a doctor if they are pregnant, might be pregnant, or are breastfeeding before taking azithromycin. If a nursing infant develops side effects while the parent is taking azithromycin, call a doctor for advice.

The brand name version of azithromycin (Zithromax) is typically more expensive than the generic version.

However, the price may vary depending on the pharmacy, a person’s insurance coverage and deductibles, and their geographic location.

Azithromycin treats many of the same infections that drugs such as penicillin and amoxicillin can treat.

A doctor may prescribe azithromycin as an alternative to other antibiotics because it typically requires a shorter course. It is also a good option for people with a history of allergies to other medications, or when other antibiotics do not work.

Because the risk of heart health problems is higher with azithromycin than with some other antibiotics, people with heart disease or arrhythmias should ask their doctor about trying a different antibiotic.

Azithromycin is an antibiotic that can treat many types of bacterial infection. It can also prevent these infections from getting worse or spreading.

Like all antibiotics, it presents some risks, so it is important to only take it under the guidance of a medical professional.