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Brian J. Werth

, PharmD, University of Washington School of Pharmacy

Last full review/revision Jul 2020| Content last modified Jul 2020
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Macrolides are a class of antibiotics that are often used to treat infections in people who are allergic to penicillins.

Macrolides include the following:

  • Azithromycin

  • Clarithromycin

  • Erythromycin

  • Fidaxomicin

Macrolides work by preventing bacteria from producing proteins they need to grow and multiply.

Fidaxomicin is given only by mouth (orally) and is minimally absorbed into the bloodstream when taken orally. It is used to treat Clostridioides difficileinduced colitis but does not do much harm to the other bacteria that normally live in healthy intestines.

Macrolides interact with many other drugs (called a drug-drug interaction). Often, the interaction increases the effects, including the side effects, of the other drugs. When given with certain other drugs, macrolides can increase the risk of sudden cardiac death in people who have long QT syndrome.




Common Uses

Some Side Effects





Respiratory infections

For azithromycin: Chlamydial infections of the reproductive organs and urinary tract

For fidaxomicin: Used only for Clostridioides difficile

Abdominal pain, nausea, vomiting, and diarrhea (especially at higher doses)


Abnormal heart rhythms (arrhythmias)*

* These side effects are not reported with fidaxomicin.

Use of Macrolides During Pregnancy and Breastfeeding

Macrolides should be taken during pregnancy only when the benefits of treatment outweigh the risks.

With erythromycin, azithromycin, and fidaxomicin, no harmful effects on the fetus have been observed in animal studies, but no well-designed studies have been done in pregnant women. Erythromycin is considered among the safest antibiotics to use during pregnancy. It is considered safer than azithromycin because it has been used more, and thus more is known about it.

With the macrolide clarithromycin, harmful effects on the fetus have been observed in animal studies. (See also Drug Use During Pregnancy.)

Use of erythromycin during breastfeeding is generally considered acceptable. Whether other macrolides are safe to use during breastfeeding is unknown. (See also Drug Use During Breastfeeding.)

Drugs Mentioned In This Article

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