Different antibiotic options including azithromycin and erythromycin

Azithromycin vs. Erythromycin: How Are They Different?

Written on August 22, 2023 by Theresa Vuskovich, DMD. To give you technically accurate, evidence-based information, content published on the Everlywell blog is reviewed by credentialed professionals with expertise in medical and bioscience fields.

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The antibiotics azithromycin and erythromycin are used to treat a wide variety of bacterial infections. [1-5] Azithromycin and erythromycin are both macrolide antibiotics, but they differ in some ways. This article discusses azithromycin vs. erythromycin and how they diverge in their uses, side effects, and drug interactions.

Azithromycin Is Prescribed for Some Adults With Chlamydia

According to the Centers for Disease Control and Prevention (CDC), azithromycin is an alternative treatment option for adults with chlamydia.[3] Chlamydia is a common bacterial sexually transmitted infection (STI) associated with long-term consequences for individuals assigned female at birth (AFAB) if left untreated.[3] Untreated chlamydia can lead to infertility, pelvic inflammatory disease (PID), and long-term abdominal pain.[3]

Chlamydia does not usually cause symptoms, but some individuals do experience the following:

  • Pain when urinating
  • Vaginal or penile discharge
  • Pain during intercourse
  • Pelvic pain

The best way to prevent chlamydia is through safe sex practices, and knowing your STI status is essential for protecting your partner. Using Everlywell's at-home chlamydia test you can test your STI status discreetly and access your results online.

For adults who test positive for chlamydia, doxycycline (tetracycline antibiotic) is most commonly prescribed.[3] After chlamydia treatment, individuals should abstain from sexual activity seven days after a single dose or until the 7-day regimen is complete.[3] To avoid reinfection, it is also important to abstain from sexual intercourse until your partner is tested.[3]

While doxycycline is most commonly prescribed for chlamydia, the CDC recommends individuals with a tetracycline allergy or women who are pregnant take azithromycin (1 g oral dose) instead.[3] Treating chlamydia during pregnancy can prevent the transmission of chlamydia to the baby.[3] The CDC does not recommend using erythromycin for treating chlamydia in adults due to the risk of gastrointestinal (GI) side effects.[3]

Erythromycin is commonly prescribed for acne, uncomplicated skin infections, and bowel preparation before GI surgery.[4] Aside from chlamydia, azithromycin is prescribed for sinus infections, tonsilitis, bronchitis, middle ear infections, and genital ulcers in individuals assigned male at birth (AMAB).[4,5]

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Erythromycin Has a Higher Risk of Gastrointestinal Side Effects

Compared to azithromycin, erythromycin has a greater risk of GI side effects.[3,4] Common GI side effects are nausea, vomiting, abdominal pain, and diarrhea.[4] Additional potential side effects of erythromycin include:[4]

  • Dizziness
  • Reversible hearing loss
  • Ringing in the ears

Azithromycin can also cause GI effects, but your risk is generally lower.[4] You can take azithromycin with or without food, and eating food before taking your medication may decrease GI discomfort.[4]

The amount you take can also affect your risk of GI and other side effects.[5] Individuals taking a single 1-gram dose rather than a multi-day regimen were more likely to experience diarrhea, nausea, abdominal pain, vomiting, indigestion, and vaginal inflammation.[5] Other more serious side effects of azithromycin are QT-interval prolongation ( abnormal heart rhythm) and liver toxicity.[4,5]

Azithromycin Has a Lower Risk of Drug Interactions

Compared to erythromycin, azithromycin has a lower risk of drug interactions.[4] However, azithromycin can interact with warfarin (blood thinner) and nelfinavir (protease inhibitor for HIV).[5] Though the risk is low, azithromycin can enhance the blood thinning effect of warfarin.[5]

Erythromycin can also interact with warfarin in addition to the commonly prescribed lipid-lowering drugs, simvastatin and lovastatin.[4] Other potential drug interactions can occur with midazolam, triazolam, theophylline, tacrolimus, cyclosporine, and ergot alkaloids.[4] This is not a comprehensive list of potential drug interactions. Consequently, it is important to inform your healthcare provider about all the medications and supplements you are taking to prevent possible drug interactions.

What To Know If You Are Prescribed Azithromycin or Erythromycin

If you are prescribed azithromycin or erythromycin, here are some important points to remember:[5]

  • Be sure to disclose all medications and supplements you are taking to your healthcare provider.
  • Ensure your healthcare provider is aware of any allergic reactions you have experienced while taking antibiotics.
  • Take your prescription as your healthcare provider prescribes, and continue taking the prescription even if symptoms disappear.
  • Take azithromycin or erythromycin with or without food.
  • Consult your healthcare provider if GI side effects occur.
  • Call 911 immediately if you experience signs of a severe reaction, such as difficulty breathing or chest pain.

Exceptional Care Is At Your Fingertips With Virtual Care Visits

Through EverlyWell, you can access STD treatment online to get answers to your health questions. You can address your symptoms with the right tests, prescriptions, or lifestyle recommendations during a virtual care visit with a licensed nurse practitioner. Your licensed nurse practitioner can provide one-time prescriptions for urinary tract infections (UTIs), minor skin infections, COVID-19, or a cold. Virtual care visits allow you to get care from the comfort of your own home.

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  1. Amsden GW. Erythromycin, clarithromycin, and azithromycin: are the differences real? Clin Ther. 1996;18(1):56-55. doi:10.1016/s0149-2918(96)80179-2. https://pubmed.ncbi.nlm.nih.gov/8851453/
  2. Patel PH, Hashmi MF. Macrolides. StatPearls Publishing; 2023. https://www.ncbi.nlm.nih.gov/books/NBK551495/ .
  3. Chlamydial infections. Centers for Disease Control and Prevention. Published August 15, 2022. Accessed August 1, 2023. https://www.cdc.gov/std/treatment-guidelines/chlamydia.htm.
  4. Werth BJ. Macrolides. Merck Manuals Professional Edition. Accessed August 1, 2023. https://www.merckmanuals.com/professional/infectious-diseases/bacteria-and-antibacterial-drugs/macrolides?query=macrolides
  5. Zithromax ® prescribing information. Food and Drug Administration. Accessed August 1, 2023. https://www.accessdata.fda.gov/drugsatfda_docs/label/2017/050710s44-050711s41-050784s28lbl.pdf
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