ERYTHROMYCIN STEARATE

Clinical safety rating: safe

Inhibits CYP3A4 increasing levels of many drugs (eg statins carbamazepine) May cause QT prolongation and subsequent arrhythmias.

How it works

Erythromycin is a macrolide antibiotic that binds to the 50S ribosomal subunit of susceptible bacteria, inhibiting protein synthesis by blocking the translocation of peptides.

What the body does with it

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.

Classification & Brands

Dosing & administration

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.

Use during pregnancy

1st trimester	Consult provider
2nd trimester	Consult provider
3rd trimester	Consult provider

Clinical note

Inhibits CYP3A4 increasing levels of many drugs (eg statins carbamazepine) May cause QT prolongation and subsequent arrhythmias.

FDA category	Human
Breastfeeding	Erythromycin is excreted into breast milk with an M/P ratio of approximately 0.5. Concentrations are low and considered compatible with breastfeeding. Monitor for potential infant gastrointestinal disturbance or rash.
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.

Warnings & precautions

■ FDA Black Box Warning

Not applicable (no FDA black box warning for erythromycin stearate).

Side Effect Profile

Common Effects	Nausea
Serious Effects

Absolute Contraindications

Hypersensitivity to erythromycin or any macrolide; concomitant use with ergotamine or dihydroergotamine; concomitant use with cisapride, pimozide, or lovastatin/simvastatin (due to increased risk of rhabdomyolysis).

Clinical Precautions

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).

Clinical Tips & Counseling

Drug interactions

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ERYTHROMYCIN STEARATE

Clinical safety rating: safe

Inhibits CYP3A4 increasing levels of many drugs (eg statins carbamazepine) May cause QT prolongation and subsequent arrhythmias.

How it works

Erythromycin is a macrolide antibiotic that binds to the 50S ribosomal subunit of susceptible bacteria, inhibiting protein synthesis by blocking the translocation of peptides.

What the body does with it

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.

Classification & Brands

Dosing & administration

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.

Use during pregnancy

1st trimester	Consult provider
2nd trimester	Consult provider
3rd trimester	Consult provider

Clinical note

Inhibits CYP3A4 increasing levels of many drugs (eg statins carbamazepine) May cause QT prolongation and subsequent arrhythmias.

FDA category	Human
Breastfeeding	Erythromycin is excreted into breast milk with an M/P ratio of approximately 0.5. Concentrations are low and considered compatible with breastfeeding. Monitor for potential infant gastrointestinal disturbance or rash.
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.

Warnings & precautions

■ FDA Black Box Warning

Not applicable (no FDA black box warning for erythromycin stearate).

Side Effect Profile

Common Effects	Nausea
Serious Effects