ERYTHROCIN
Clinical safety rating: caution
Comprehensive clinical and safety monograph for ERYTHROCIN (ERYTHROCIN).
Erythromycin is a macrolide antibiotic that binds to the 50S subunit of the bacterial ribosome, inhibiting protein synthesis by blocking translocation of peptidyl-tRNA. It also exhibits anti-inflammatory and prokinetic effects via motilin receptor agonism.
| Metabolism | Primarily metabolized by CYP3A4 isoenzyme in the liver; undergoes demethylation and N-demethylation; major metabolite is N-desmethylerythromycin. |
| Excretion | Primarily eliminated via biliary excretion as unchanged drug and metabolites; approximately 2-5% excreted renally as active drug, 15-20% as metabolites; up to 30% excreted in feces. |
| Half-life | Terminal elimination half-life is approximately 1.5-2 hours in adults; may prolong to 4-6 hours in hepatic impairment or neonates. |
| Protein binding | Approximately 70-90% bound, primarily to albumin and alpha-1-acid glycoprotein. |
| Volume of Distribution | Vd approximately 0.6-0.9 L/kg, indicating distribution into total body water and tissues; higher in children (0.8-1.2 L/kg). |
| Bioavailability | Oral: 30-65% (variable due to acid lability; enhanced by enteric coating); intramuscular: 70-80%; intravenous: 100%. |
| Onset of Action | Oral: 1-2 hours; intravenous: immediate (within minutes); topical: delayed, clinical effect seen within 2-3 weeks for acne. |
| Duration of Action | Oral and intravenous: 6-12 hours (bacteriostatic action persists while concentrations above MIC); topical: continuous with daily application. |
| Action Class | Macrolides |
| Brand Substitutes | Erythromycin Estol 500mg Tablet, Eryster 500mg Tablet, Eltocin 500mg Tablet, Erytho 500mg Tablet, Elucin 500mg Tablet, Agrocin 250mg Tablet, Eryster 250mg Tablet, Erythrokem 250mg Tablet, Erythrotone 250mg Tablet, E Mycin 250mg Tablet, Ticin Suspension, Ortholate Suspension, E Mycin 100mg Suspension, Methro Suspension, Althrocin 100mg Tablet, Ortholate 100mg Tablet, T Mycin 100mg Tablet, Erocin 100mg Tablet |
250-500 mg orally every 6 hours or 500 mg to 1 g intravenously every 6 hours.
| Dosage form | INJECTABLE |
| Renal impairment | Erythromycin is primarily hepatically eliminated; no dose adjustment required for renal impairment, but caution in severe renal failure (CrCl <10 mL/min) due to potential ototoxicity. |
| Liver impairment | In Child-Pugh class A: usual dose; class B: reduce dose by 50% or extend interval; class C: avoid or use with extreme caution with 75% dose reduction. |
| Pediatric use | 30-50 mg/kg/day orally divided every 6 hours, or 20-40 mg/kg/day intravenously divided every 6 hours; maximum 2 g/day. |
| Geriatric use | No specific dose adjustment; use caution due to increased risk of QT prolongation and hearing loss; monitor electrolytes and ECG. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for ERYTHROCIN (ERYTHROCIN).
| Breastfeeding | Compatible with breastfeeding. Erythromycin is excreted into breast milk in small amounts (M/P ratio approximately 0.5). The estimated daily infant dose is 1-2% of maternal weight-adjusted dose. No adverse effects reported in breastfeeding infants. Caution with maternal high doses may cause diarrhea or candidiasis in the infant. |
| Teratogenic Risk | Category B: No evidence of teratogenicity in animal studies; limited human studies show no increased risk of major malformations. Fetal risk cannot be excluded but appears low. Use only if clearly needed. |
■ FDA Black Box Warning
Erythromycin may prolong the QT interval and increase the risk of ventricular arrhythmias, including torsades de pointes, especially in patients with pre-existing QT prolongation, electrolyte disturbances, or concomitant use of other QT-prolonging drugs.
| Serious Effects |
Hypersensitivity to erythromycin or any macrolide antibiotic; pre-existing QT prolongation or history of torsades de pointes; concomitant use with CYP3A4 substrates that prolong QT (e.g., cisapride, pimozide, astemizole, terfenadine); hepatic impairment (relative).
| Precautions | QT prolongation and risk of arrhythmias; hepatotoxicity (elevated liver enzymes, cholestatic hepatitis); exacerbation of myasthenia gravis; increased risk of pyloric stenosis in neonates (oral use); Clostridioides difficile-associated diarrhea; drug interactions via CYP3A4 inhibition (e.g., statins, warfarin, ergotamine). |
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| Fetal Monitoring |
| Maternal: Assess for gastrointestinal intolerance, QT prolongation (especially with electrolyte disturbances or concurrent QT-prolonging drugs), hepatotoxicity, and allergic reactions. Fetal: Non-stress test or biophysical profile if used for preterm premature rupture of membranes to monitor for chorioamnionitis; no specific fetal monitoring for drug toxicity required. |
| Fertility Effects | No known adverse effects on human fertility. Animal studies show no impairment of fertility at therapeutic doses. |