Macrolide antibiotic

Erythromycin

Brand names: Erythrocin, Erymax

Adult dose

Dose: 250–500mg QDS PO; 50mg/kg/day IV in 4 divided doses (severe infection)

Route: PO / IV

Frequency: QDS

Clinical pearls

NICE CKS / BNF: alternative to penicillin in penicillin-allergic patients
UKHSA: pertussis treatment first-line in late pregnancy/neonates
MHRA cardiac and infantile pyloric stenosis warnings
Used in low dose for prokinesis (off-label) in gastroparesis

Contraindications

Hypersensitivity to macrolides
Concurrent ergot alkaloids
Concurrent astemizole/terfenadine/cisapride
Concurrent lovastatin/simvastatin
Severe hepatic impairment

Side effects

GI upset (very common — motilin agonism)
QT prolongation / torsades
Hepatotoxicity (cholestatic, especially estolate salt)
Reversible hearing loss (high-dose IV)
C. difficile
Pyloric stenosis (neonates)

Interactions

Strong CYP3A4 substrate inhibition — many: warfarin, statins (myopathy), digoxin, theophylline, calcineurin inhibitors, ergots, midazolam
QT-prolonging drugs

Monitoring

LFTs
ECG (QT) if risk factors
Drug interaction review at every prescription

Reference: BNF; NICE CKS; UKHSA; MHRA Drug Safety Update; https://bnf.nice.org.uk/drugs/erythromycin/. Verify against your local formulary and the latest BNF before prescribing.

Curated clinical cross-links plus same-class fallbacks.

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