[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [Macrolides](https://durgical.com/en/pharmacology/classes/macrolides/) › Erythromycin

[Pharmacology](https://durgical.com/en/pharmacology/) · [Macrolides](https://durgical.com/en/pharmacology/classes/macrolides/)

# Erythromycin

The first macrolide. Still used as an eye ointment for newborns and as an alternative to penicillin; it also stirs the gut via motilin receptors.

Updated 2026-11-01

- Class: [Macrolides](https://durgical.com/en/pharmacology/classes/macrolides/)
- Target: Bacterial ribosome, 50S subunit (23S rRNA, exit tunnel)
- ATC code: J01FA01
- WHO Model List of Essential Medicines

◆**Bacterial ribosome, 50S subunit (23S rRNA, exit tunnel)**Erythromycin

ⓘ The figure shows erythromycin bound in the exit tunnel of the Escherichia coli ribosome.

**Target in 3D:** Bacterial ribosome, 50S subunit (23S rRNA, exit tunnel). PDB structure 4V7U (RCSB PDB, public domain). [View the structure at RCSB PDB](https://www.rcsb.org/structure/4V7U) · Drag to rotate · pinch to zoom

## Mechanism of action

Erythromycin binds the 23S rRNA in the exit tunnel of the 50S subunit and stops the growing protein chain. It is unstable in stomach acid, so oral forms are protected salts or esters. It also binds and activates the motilin receptor of the gut, which explains its cramps and diarrhoea, and it inhibits CYP3A4.

- Reaches the bacterium after absorption or local application
- Binds the 23S rRNA in the 50S exit tunnel
- The nascent protein cannot pass
- Bacterial growth stops

## Pharmacokinetics

**Absorption**
Destroyed by stomach acid; oral products are coated or given as salts and esters. IV form (lactobionate) and eye ointment exist.

**Metabolism**
Liver; it inhibits CYP3A4.

**Elimination**
Concentrated in the liver and excreted in the bile.

## Indications

- Streptococcal pharyngitis and prevention of rheumatic fever in people allergic to penicillin [Streptococcal pharyngitis →](https://durgical.com/en/conditions/streptococcal-pharyngitis/)
- Respiratory infections, including Legionnaires' disease and Mycoplasma pneumonia [Community-acquired pneumonia →](https://durgical.com/en/conditions/community-acquired-pneumonia/)
- Prevention of ophthalmia neonatorum due to N. gonorrhoeae or C. trachomatis (eye ointment) [Conjunctivitis →](https://durgical.com/en/conditions/conjunctivitis/)
- Diphtheria carriers, together with antitoxin

## Adverse effects

### Common

- Abdominal cramps, nausea, vomiting and diarrhoea
- Pain and vein irritation with the IV form
- Rash

### Serious (rare, important)

- QT prolongation and torsades de pointes, especially with the IV form
- Infantile hypertrophic pyloric stenosis after use in young infants
- Reversible hearing loss with high doses, mainly in older people with kidney or liver impairment
- Hepatotoxicity and C. difficile colitis

## Contraindications

- Allergy to erythromycin
- Use with terfenadine, astemizole, cisapride, pimozide, ergotamine or dihydroergotamine
- Use with lovastatin or simvastatin

## Key interactions

**Simvastatin and lovastatin**
Higher risk of myopathy and rhabdomyolysis (CYP3A4).

**Pimozide, cisapride and other QT drugs**
Dangerous arrhythmias.

**Other CYP3A4 substrates (e.g. carbamazepine, ciclosporin)**
Their levels rise.

## What is monitored

- ECG with IV use or QT risk
- Hearing with high doses in older patients
- Liver tests if symptoms; vomiting in infants

## Administration and safety

- The IV form is infused slowly and diluted, preferably as a continuous or intermittent infusion, to limit vein pain
- Never given as an IV push
- The eye ointment is applied once to both eyes of the newborn

## Nursing care

- Check the IV site for pain and phlebitis
- Warn about cramps and nausea
- Review the medication list for statins and QT drugs
- In infants, ask the family to report vomiting after feeds

## Pregnancy and breastfeeding

Crosses the placenta and reaches breast milk; in pregnancy it is used when the benefit justifies the risk.

## Memory aid

«Erythro wakes the gut»: it pushes motilin's button, so the stomach empties fast and the patient feels the cramps.

## Test yourself

Think of the answer, then tap the question to see it.

## Why does erythromycin cause abdominal cramps?

It activates the motilin receptor in the gut and increases gut motility.

## Which newborn use does erythromycin eye ointment have?

Prevention of ophthalmia neonatorum caused by gonococcus or chlamydia.

## Which serious infant problem has been linked to erythromycin?

Infantile hypertrophic pyloric stenosis.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/pharmacology/erythromycin/)

## Related drugs

- [Azithromycin](https://durgical.com/en/pharmacology/azithromycin/)
- [Clarithromycin](https://durgical.com/en/pharmacology/clarithromycin/)

## Related conditions

- [Streptococcal pharyngitis](https://durgical.com/en/conditions/streptococcal-pharyngitis/)
- [Community-acquired pneumonia](https://durgical.com/en/conditions/community-acquired-pneumonia/)
- [Conjunctivitis](https://durgical.com/en/conditions/conjunctivitis/)

[← Back to the class: Macrolides](https://durgical.com/en/pharmacology/classes/macrolides/)

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: [DailyMed - ERYTHROMYCIN LACTOBIONATE injection, powder, for solution](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=ee345752-0f0c-c69b-e053-2995a90a7dac) (DailyMed (U.S. National Library of Medicine), 2026); [DailyMed - ERYTHROMYCIN ointment](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=061ddd20-94a6-4e3c-ba84-1ebd8529eea6) (DailyMed (U.S. National Library of Medicine), 2026); [Erythromycin: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a682381.html) (MedlinePlus (U.S. National Library of Medicine), 2026); [Cryo-EM structure of the erythromycin-bound motilin receptor-Gq protein complex](https://www.rcsb.org/structure/8IBU) (RCSB Protein Data Bank, 2026).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/pharmacology/erythromycin/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/erythromycin/