E-MYCIN
Clinical safety rating: caution
Comprehensive clinical and safety monograph for E-MYCIN (E-MYCIN).
Erythromycin binds to the 50S ribosomal subunit of susceptible bacteria, inhibiting protein synthesis by blocking the translocation of peptidyl-tRNA. It may also act as a motilin receptor agonist, enhancing gastrointestinal motility.
| Metabolism | Erythromycin is primarily metabolized by the liver via CYP3A4 isoenzyme. It undergoes demethylation and hydroxylation, producing active and inactive metabolites. |
| Excretion | Primarily hepatic metabolism and biliary excretion with significant enterohepatic circulation; approximately 2-15% excreted unchanged in urine; 10-40% excreted in feces via bile; less than 1% eliminated as unchanged drug in feces from unabsorbed drug. |
| Half-life | 1.5-2 hours in adults with normal renal function; prolonged to 4-6 hours in severe hepatic impairment; no significant change in renal impairment due to minimal renal clearance. |
| Protein binding | 65-90% bound primarily to albumin, with concentration-dependent binding; at therapeutic levels ~70-80% bound. |
| Volume of Distribution | 0.5-1.2 L/kg, indicating extensive tissue distribution; concentrates in tissues (e.g., liver, spleen, tonsils) and intracellularly in phagocytes. |
| Bioavailability | Oral base: ~30-40% (acid-labile; enteric-coated preparations improve); estolate: ~100% (due to enhanced absorption and decreased first-pass); stearate and ethylsuccinate: ~40-60% (fasting reduces absorption of stearate; ethylsuccinate absorption is food-dependent). |
| Onset of Action | Oral (base/estolate): 1 hour; Oral (stearate/ethylsuccinate): 1-2 hours; IV: within 30 minutes. |
| Duration of Action | Oral: 6-12 hours (sustained for at least 6 hours); IV: duration of infusion and post-infusion levels; clinical effect persists for 6-12 hours depending on dose and formulation. |
250-500 mg orally every 6 hours or 500 mg every 12 hours; maximum 4 g/day.
| Dosage form | TABLET, DELAYED RELEASE |
| Renal impairment | No adjustment needed for mild to moderate renal impairment. For GFR <10 mL/min, use 50-60% of normal dose. |
| Liver impairment | Reduce dose by 50% in Child-Pugh class C cirrhosis; avoid in severe hepatic impairment. |
| Pediatric use | 30-50 mg/kg/day orally divided every 6 hours; maximum 2 g/day. |
| Geriatric use | Use lower end of dose range (250-500 mg every 6 hours) due to increased risk of QT prolongation and drug interactions. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for E-MYCIN (E-MYCIN).
| Breastfeeding | Erythromycin is excreted into human breast milk in small amounts. The average milk-to-plasma ratio is approximately 0.5. Levels are usually low, but can accumulate with high maternal doses. No adverse effects have been reported in breastfed infants, though there is a theoretical risk of alteration in infant gut flora or drug resistance. The American Academy of Pediatrics considers erythromycin compatible with breastfeeding. Caution with prolonged or high-dose therapy due to risk of infant gastrointestinal effects. |
| Teratogenic Risk | E-MYCIN (erythromycin base) is generally considered low risk in pregnancy. Data from large cohort studies and meta-analyses do not show an increased risk of major congenital malformations after first trimester exposure. However, erythromycin estolate has been associated with an increased risk of maternal hepatotoxicity; preparations other than estolate are preferred. During second and third trimesters, erythromycin has been used for the treatment of genital mycoplasma infections and for Group B Streptococcus prophylaxis. There is a possible increase in pyloric stenosis risk in infants exposed in utero, particularly when used late in pregnancy, but absolute risk remains low. Use only if clearly needed. |
■ FDA Black Box Warning
E-MYCIN does not have a black box warning.
| Serious Effects |
["Hypersensitivity to erythromycin or any macrolide antibiotic","Concomitant use with ergotamine or dihydroergotamine (ergotism risk)","Concomitant use with cisapride, pimozide, astemizole, terfenadine, or other QT-prolonging agents (risk of torsades de pointes)","History of cholestatic jaundice or hepatic impairment associated with prior erythromycin use"]
| Precautions | ["Hepatic dysfunction: may cause cholestatic hepatitis, especially with estolate salt","Prolongation of QT interval and risk of torsades de pointes, especially with other QT-prolonging drugs or electrolyte abnormalities","Infantile hypertrophic pyloric stenosis (IHPS) in neonates exposed to erythromycin","Clostridioides difficile-associated diarrhea (CDAD)","Exacerbation of myasthenia gravis","Ototoxicity (reversible, mainly with high doses or renal impairment)","Antagonism with clindamycin and chloramphenicol"] |
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| Fetal Monitoring | Routine maternal monitoring for gastrointestinal adverse effects (nausea, vomiting, diarrhea, abdominal pain) and potential hepatotoxicity (especially with estolate salt). Monitor for signs of Clostridioides difficile infection. In neonates exposed near term, observe for signs of pyloric stenosis (projectile vomiting, electrolyte disturbances) for the first few weeks of life. |
| Fertility Effects | No known adverse effects on fertility or reproductive function in humans. Erythromycin does not appear to impair spermatogenesis or ovulation in animal studies or reported clinical data. |