Macrolide antibiotic 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, Erymax

Erythromycin is a macrolide antibacterial used for respiratory, skin and soft-tissue infections and as an alternative in penicillin-allergic patients, and it also has prokinetic gastrointestinal effects.

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). 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 bacterial 50S ribosomal subunit and inhibits protein synthesis; its prokinetic action results from agonism at motilin receptors in the gut.

Prescribing in practice

It prolongs the QT interval and is a potent CYP3A4 and P-glycoprotein inhibitor, so it carries a high risk of serious interactions and arrhythmias; review concomitant drugs carefully.
Gastrointestinal upset (nausea, vomiting, cramps) is very common and can limit tolerability.
Use in early infancy has been associated with infantile hypertrophic pyloric stenosis.

Monitoring

Monitor for gastrointestinal effects, hepatic function with prolonged use, and QT prolongation or interactions in at-risk patients.

Counselling the patient

Tell your team about all other medicines, as erythromycin interacts with many drugs.
Report palpitations, fainting or an irregular heartbeat.
Take as directed and complete the prescribed course.

Evidence & guidelines

The MHRA has highlighted the risk of QT prolongation and drug interactions with macrolides including erythromycin.

Reference: NICE CKS; UKHSA; MHRA Drug Safety Update; 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.

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