First-Generation Macrolide — Penicillin Allergy Alternative / Gastroparesis Prokinetic Pregnancy: Should be used during pregnancy only if clearly needed; conflicting epidemiological data on congenital malformations; possible association with infantile hypertrophic pyloric stenosis (UK SPC §4.6)

Erythromycin

Brand names: Erythrocin, Erythroped, Tiloryth

Erythromycin is a macrolide antibiotic used for respiratory, skin and soft tissue and genital infections, particularly as an alternative in penicillin allergy, and exploited at low doses for its gastrointestinal prokinetic effect.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: 250 mg to 500 mg

Route: Oral

Frequency: Every six hours

Max: 4 g daily (for more severe infections)

UK SPC (oral suspension), infection use. Adults, including elderly, and children over 8 years: 250-500 mg every six hours, up to 4 g daily for more severe infections. Acne vulgaris: usual dose 250 mg three times daily before meals for one to four weeks, then reduced to twice daily until improvement occurs. Paediatric (oral): children 2 to 8 years 250 mg every six hours (doubled for severe infections) or 30 mg/kg/day in divided doses (up to 50 mg/kg/day for severe infections); children up to 2 years 125 mg every six hours (doubled for severe infections) or 30 mg/kg/day in divided doses (up to 50 mg/kg/day for severe infections). Clinician to verify paediatric dosing against a children's formulary.

Dose adjustments

Renal

If impairment is severe (GFR <10 ml/min), the daily dose should not exceed 1.5 g due to risk of ototoxicity

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Hypersensitivity to the active substance or to any of the excipients
Concomitant use with simvastatin, tolterodine, mizolastine, amisulpride, astemizole, terfenadine, domperidone, cisapride or pimozide
Concomitant use with ergotamine, dihydroergotamine, or lomitapide
History of QT prolongation (congenital or acquired) or ventricular arrhythmia including torsades de pointes
Electrolyte disturbances (hypokalaemia, hypomagnesaemia)

Side effects

Gastrointestinal effects — upper abdominal discomfort, nausea, vomiting, diarrhoea (most frequent, dose-related)
QTc interval prolongation, torsades de pointes, palpitations, ventricular tachyarrhythmias
Allergic reactions ranging from urticaria and mild skin eruptions to anaphylaxis
Cholestatic hepatitis, jaundice, hepatic dysfunction, hepatic failure
Reversible hearing loss (chiefly in renal insufficiency or high doses), tinnitus

Interactions

Simvastatin, tolterodine, mizolastine, amisulpride, astemizole, terfenadine, domperidone, cisapride, pimozide (contraindicated)
Ergotamine and dihydroergotamine (contraindicated)
Lomitapide (contraindicated)
Other medicinal products associated with QT prolongation (caution — risk of arrhythmia/torsades)

Clinical monograph

How it works

It binds the 50S bacterial ribosomal subunit and inhibits protein synthesis by blocking translocation; its motilin-receptor agonism underlies its prokinetic action.

Prescribing in practice

Erythromycin prolongs the QT interval and inhibits CYP3A, so it can cause serious arrhythmias, especially with other QT-prolonging or interacting drugs such as some statins, which should be reviewed.
It frequently causes dose-related gastrointestinal upset including nausea, cramps and diarrhoea.
Use in early infancy has been associated with infantile hypertrophic pyloric stenosis.

Monitoring

Routine monitoring is not generally required, but assess for interactions and consider cardiac risk in susceptible patients.

Counselling the patient

Take as directed and complete the course even once feeling better.
Report palpitations or fainting promptly.
Tell your prescriber about all other medicines, as erythromycin interacts with many.

Evidence & guidelines

Erythromycin is a long-established macrolide retained in UK antimicrobial guidance as a penicillin-allergy alternative.

Reference: PHE Antibiotic Guidelines; NICE Pertussis Guidance; MHRA QT Prolongation Guidance; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways