ERYTHROMYCIN STEARATE
Clinical safety rating: safe
Inhibits CYP3A4 increasing levels of many drugs (eg statins carbamazepine) May cause QT prolongation and subsequent arrhythmias.
Erythromycin is a macrolide antibiotic that binds to the 50S ribosomal subunit of susceptible bacteria, inhibiting protein synthesis by blocking the translocation of peptides.
| Metabolism | Primarily hepatic via CYP3A4; undergoes demethylation and conjugation; eliminated mainly in bile with some renal excretion. |
| Excretion | Primarily excreted in bile as active drug; about 2-5% excreted renally as unchanged drug. Up to 15% excreted in feces. |
| Half-life | 1.4-2 hours in adults with normal renal function; prolonged to 5-6 hours in anuria; unchanged in hepatic impairment. |
| Protein binding | 75-90% bound, primarily to alpha-1-acid glycoprotein. |
| Volume of Distribution | 0.6-1.2 L/kg; indicates extensive tissue penetration. |
| Bioavailability | Oral erythromycin stearate: 30-65% (variable, reduced by food). |
| Onset of Action | Oral: 1-2 hours after administration; IV: within 30 minutes. |
| Duration of Action | 6-12 hours for susceptible organisms; dosing every 6 hours advised for sustained effect. |
| Molecular Weight | 733.93 |
250-500 mg orally every 6 hours or 500-1000 mg orally every 12 hours; maximum 4 g/day.
| Dosage form | TABLET |
| Renal impairment | No dose adjustment required for mild to moderate renal impairment. For severe renal impairment (eGFR <10 mL/min), consider reducing dose by 50% or increasing dosing interval to every 12-24 hours due to potential accumulation. |
| Liver impairment | Contraindicated in patients with pre-existing liver disease or hepatic impairment. Use with caution and monitor liver function; no specific Child-Pugh based recommendations, but avoid in severe hepatic dysfunction. |
| Pediatric use | 30-50 mg/kg/day orally in divided doses every 6 hours; not to exceed 2 g/day. For infants and children, weight-based dosing is preferred. |
| Geriatric use | No specific dose adjustment in elderly, but may have increased risk of QT prolongation and hearing loss; use lower end of dosing range and monitor renal function and electrolytes. |
| 1st trimester | Crosses placenta; no evidence of teratogenicity in humans but avoid unless clearly needed. |
| 2nd trimester | Considered safe; use if indicated for infections like chlamydia or syphilis. |
| 3rd trimester | Considered safe; risk of infantile hypertrophic pyloric stenosis is rare and not trimester-specific. |
Clinical note
Inhibits CYP3A4 increasing levels of many drugs (eg statins carbamazepine) May cause QT prolongation and subsequent arrhythmias.
| FDA category | Human |
| Placental transfer | Crosses placenta; fetal serum levels approximately 5-20% of maternal serum levels. |
| Breastfeeding | Erythromycin is excreted into breast milk in small amounts (less than 2% of maternal dose). Not expected to cause adverse effects in nursing infants. However, monitor for gastrointestinal disturbances or potential alteration of infant gut flora. |
■ FDA Black Box Warning
Not applicable (no FDA black box warning for erythromycin stearate).
| Common Effects | Nausea |
| Serious Effects |
Hypersensitivity to erythromycin or any macrolide antibioticConcomitant use with cisapride, pimozide, astemizole, terfenadine, or ergot alkaloids (risk of QT prolongation and torsades de pointes)Pre-existing QT interval prolongation or history of torsades de pointes
| Precautions | Potential for QT prolongation and torsades de pointes, especially with other QT-prolonging agents; caution in hepatic impairment; may exacerbate myasthenia gravis; risk of infantile hypertrophic pyloric stenosis in neonates; Clostridium difficile-associated diarrhea; ototoxicity (especially with high doses or renal impairment). |
| Food/Dietary | Grapefruit juice inhibits CYP3A4-mediated metabolism of erythromycin, potentially increasing drug levels and risk of toxicity. Avoid grapefruit products during therapy. Food, especially high-fat meals, delays and reduces absorption; take on an empty stomach with water only. |
Loading safety data…
| Lactation Rating | L2 (Safer) |
| Teratogenic Risk | Most studies show no increased risk of major malformations with erythromycin use during pregnancy. However, a few retrospective studies have suggested a possible small increased risk of cardiovascular defects, particularly after first-trimester exposure. There is no evidence of fetotoxicity or adverse fetal effects from second or third trimester use. Erythromycin estolate is associated with maternal hepatotoxicity and should be avoided; stearate salt does not carry this risk. |
| Fetal Monitoring | Monitor maternal liver function tests if prolonged therapy; monitor for gastrointestinal adverse effects. No specific fetal monitoring required beyond routine prenatal care. |
| Fertility Effects | No known adverse effects on human fertility. Animal studies have not demonstrated impaired fertility. |
| Clinical Pearls | Erythromycin stearate is acid-labile; administer with a full glass of water on an empty stomach (1 hour before or 2 hours after meals) for maximal absorption. Avoid concurrent use with HMG-CoA reductase inhibitors (statins) due to increased risk of rhabdomyolysis. Erythromycin is a known QT-prolonging agent; monitor ECG in patients with electrolyte abnormalities, bradycardia, or concurrent use of other QT-prolonging drugs. Use with caution in hepatic impairment; may cause cholestatic hepatitis, especially in pregnant patients. |
| Patient Advice | Take each dose with a full glass of water on an empty stomach, at least 1 hour before or 2 hours after meals. · Do not crush or chew the tablets; swallow them whole. · Complete the entire prescribed course even if you feel better. · Report any signs of liver problems: severe stomach pain, dark urine, or yellowing of eyes/skin. · Avoid grapefruit juice and grapefruit products during treatment. · Inform your doctor if you have a history of heart rhythm problems, liver disease, or myasthenia gravis. · Use effective contraception if applicable; erythromycin may reduce the efficacy of oral contraceptives. |