Erythromycin is a macrolide antibiotic that inhibits bacterial protein synthesis by binding the 50S ribosomal subunit.
It is also a motilin-receptor agonist, which explains both its gastrointestinal side effects and its off-label use as a prokinetic for gastroparesis.
When administered alone increases risk of sudden death by 2 times and when combines with verapamil or diltiazem increased the risk by 5 fold.
Prolongs cardiac repolarization and can be associated with torsades de pointes.
Metabolized by cytochrome-P450 3A isozymes and calcium channel blockers can inhibit such metabolism increasing the plasma levels of erythromycin increasing the risk for sudden death and ventricular arrhythmias.
Selected infections caused by susceptible organisms, including some respiratory and skin infections, pertussis, and *Mycoplasma* infections.
Choice should account for the organism, susceptibility, and local resistance patterns; erythromycin does not treat viral infections.
Oral adult dose: For the cited erythromycin-base tablet formulation, the labeled usual dose is 250 mg every 6 hours or 500 mg every 12 hours.
Dose and duration depend on the infection and formulation; the label permits up to 4 g/day for severe infections.
Common adverse effects: Nausea, abdominal pain, vomiting, and diarrhea.
Key risks include gastrointestinal upset, drug–drug interactions via CYP3A4 inhibition, and QT interval prolongation leading to torsades de pointes.
Important less-common risks include QT prolongation/torsades de pointes, hepatotoxicity, C. difficile associated diarrhea, and infantile hypertrophic pyloric stenosis after neonatal exposure.
Interactions: Erythromycin inhibits CYP3A.
Avoid coadministration with simvastatin or lovastatin; check carefully for interactions with colchicine, other CYP3A substrates, and QT-prolonging drugs.
Avoid it in patients with known QT prolongation or significant uncorrected hypokalemia or hypomagnesemia.
Erythromycin has the highest QT‑prolongation/torsades risk among common macrolides; risk rises with older age, female sex, heart disease, electrolyte abnormalities, rapid/high IV dosing, and co‑prescribed QT‑prolonging or CYP3A4‑metabolized drugs
Mechanistically, macrolides block the cardiac IKr (HERG) potassium channel, prolonging repolarization and QTc.
Pharmacovigilance analyses show strong disproportional signals for long‑QT/torsades with erythromycin; most cardiac events occur within 2 weeks, often early after start.
Common: nausea, vomiting, abdominal pain, diarrhea; rare: rash, reversible hearing loss, severe cutaneous reactions; antibiotic‑associated colitis can occur.
As a CYP3A4 inhibitor, erythromycin elevates levels of co‑medications (e.g., certain statins, warfarin, benzodiazepines, antiarrhythmics), increasing toxicity risk; consider alternatives or adjust therapy
For IV use (e.g., pre‑endoscopy prokinetic in upper GI bleeding), guidelines recommend 250 mg infused over 5–30 minutes and caution about QT risk, especially with repeated/high doses or pre‑existing risk factors