Erythromycin

What is Erythromycin?

Erythromycin is a macrolide antibiotic derived from Saccharopolyspora erythraea and was one of the first macrolide antibiotics introduced into clinical practice. It is used to treat respiratory and skin infections and remains a clinically important alternative agent for sexually transmitted infections (notably chlamydia in pregnancy) and for patients with penicillin allergy.

Erythromycin is listed on the WHO Model List of Essential Medicines and has a well-established safety profile, including extensive data on use during pregnancy. While newer macrolides such as azithromycin have largely replaced erythromycin for many indications due to a more convenient dosing schedule and better gastrointestinal tolerability, erythromycin remains clinically relevant.

How does Erythromycin work?

Erythromycin inhibits bacterial protein synthesis by binding reversibly to the 50S ribosomal subunit of susceptible bacteria. Specifically, it prevents translocation — the movement of the ribosome along the messenger RNA strand — which halts the elongation of the polypeptide chain.

Key mechanisms:

• Bacteriostatic activity: At standard doses, erythromycin inhibits bacterial growth (bacteriostatic) by preventing protein synthesis, allowing the immune system to clear the infection
• Bactericidal at high concentrations: Against some organisms, erythromycin can kill bacteria at higher concentrations
• Intracellular penetration: Erythromycin concentrates within phagocytic cells (macrophages, neutrophils), making it effective against intracellular pathogens like Chlamydia trachomatis
• Spectrum: Active against gram-positive cocci, Chlamydia, Mycoplasma, Ureaplasma, and Treponema pallidum

Who is Erythromycin for?

Erythromycin’s main indications include:

• Chlamydia (alternative, particularly in pregnancy): WHO and European STI guidelines recommend erythromycin as an alternative for chlamydia treatment in pregnant women who cannot take azithromycin
• Non-gonococcal urethritis (NGU): Alternative when first-line agents are not appropriate
• Syphilis in pregnancy: Erythromycin must not be relied on to treat fetal infection. Penicillin allergy requires specialist management; erythromycin is not an adequate substitute.
• Lymphogranuloma venereum (LGV): Second-line alternative to doxycycline

Erythromycin is not appropriate for:

• Patients with known macrolide allergy
• Concurrent use of certain QT-prolonging medicines (risk of serious cardiac arrhythmia)
• Concurrent use of ergotamine or dihydroergotamine (risk of ergot toxicity)
• Patients taking pimozide, terfenadine, or astemizole

Dosage

Erythromycin is available as tablets, capsules, and oral suspension. Different forms (erythromycin base, stearate, ethylsuccinate) may have different instructions and doses. The prescribing doctor will specify the appropriate product and dose; check its leaflet for instructions on taking it with or without food.

Side effects

Gastrointestinal side effects are the most significant limitation of erythromycin and affect a large proportion of patients.

Very common side effects (affecting more than 1 in 10 people)

• Nausea
• Vomiting
• Abdominal cramping and pain
• Diarrhoea

Common side effects

• Loss of appetite
• Flatulence
• Headache

Less common but clinically significant

• Cholestatic jaundice (hepatotoxicity): Particularly with the estolate form; presents as jaundice, abdominal pain, and elevated liver enzymes — usually reversible on stopping
• QT interval prolongation: Can lead to potentially life-threatening cardiac arrhythmias (torsades de pointes), especially in combination with other QT-prolonging drugs
• Ototoxicity: Hearing loss and tinnitus, particularly with high doses and prolonged use — usually reversible

Rare but serious

• Severe allergic reactions (anaphylaxis)
• Clostridioides difficile colitis

Erythromycin vs alternative antibiotics for chlamydia

Why erythromycin is still used: Despite its gastrointestinal side effect profile, erythromycin has an extensive safety record in pregnancy and remains an established alternative when other agents are contraindicated. In non-pregnant patients, azithromycin is generally preferred as an alternative macrolide due to its single-dose convenience and better tolerability.

Online assessment for Erythromycin

Erythromycin is a prescription-only medicine (POM) in all EU member states. It cannot legally be dispensed without a valid prescription from a licensed medical professional.

Prescrivia operates as a technology intermediary: we do not prescribe medicines, employ doctors, or sell medicines. Our platform connects patients with independent doctors who can conduct confidential online health assessments.

Availability of an online assessment, prescribing, dispensing and delivery depends on the medicine, country and applicable law. Spain prohibits distance sale of prescription medicines; a catalogue entry or cross-border prescription does not establish a right to delivery. An in-person examination or testing may be required.

The process, where legally and clinically available:

1. Complete a health assessment: Describe your symptoms, pregnancy status, allergies, and current medications.
2. Doctor review: An independent doctor reviews your assessment. If erythromycin is clinically appropriate, they may issue a prescription.
3. Pharmacy fulfilment: The prescription is sent to a pharmacy partner to assess dispensing and any supply under the applicable country rules.

Important: Prescrivia does not guarantee that a prescription will be issued. All prescribing decisions are made independently by qualified medical professionals.

Important safety information

Do not take Erythromycin if you:

• Are taking simvastatin or lovastatin: concomitant use is prohibited because of the risk of myopathy, including rhabdomyolysis. Consult the prescriber before starting erythromycin; do not stop or change an existing statin treatment on your own
• Are allergic to erythromycin or other macrolide antibiotics
• Are taking pimozide, terfenadine, astemizole, cisapride, ergotamine, or dihydroergotamine (potentially fatal interactions)
• Have a history of QT prolongation or are taking other QT-prolonging medicines without specialist assessment

Tell your doctor before taking Erythromycin if you:

• Have liver disease
• Have myasthenia gravis (erythromycin may worsen muscle weakness)
• Are taking atorvastatin or other medicines that require individual interaction management by the prescriber
• Are taking warfarin (monitor INR closely)
• Are taking ciclosporin or tacrolimus (erythromycin raises their blood levels)

Drug interactions: Erythromycin is a significant CYP3A4 inhibitor. The number of potentially affected medicines is large — always provide a complete medication list to your doctor during assessment.

Sources

• Product information / clinical reference 1
• Product information / clinical reference 2
• Product information / clinical reference 3

Medical information on this page is based on the following sources:

• World Health Organization (WHO). WHO Guidelines for the Treatment of Chlamydia trachomatis. 2016. who.int
• World Health Organization (WHO). WHO Model List of Essential Medicines. 22nd edition, 2021.
• European STI Guidelines Editorial Board. 2015 European guideline on the management of Chlamydia trachomatis infections. Journal of the European Academy of Dermatology and Venereology.

The content-edit date does not certify a clinical review. It is provided for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional for advice relevant to your individual health circumstances.