Erythromycin: Ethylsuccinate VS Stearate

Drugs	Eryhthromycin Ethylsuccinate 400mg	Erythromycin Stearate 250mg
Equivalence	400mg	250mg
Frequency	Q6-12h	Q6-12h
Drugs.com          URTI/Pharygitis	Mild-moderate:  PO 400-800mg QID Severe:  IV/IVI 1-4g/day QID	Mild-moderate:  PO 250-500mg QID Severe:  IV/IVI 1-4g/day QID
Lexicomp Usual dosage range	PO 400-800 mg BD-QID.  Max 4g/day	PO 250-500mg BD-QID.  Max 4g/day
Sanford Antibiotic Guidelines Usual dosing	PO 400-800 mg BD-QID.  Max 4g/day	PO 250-500mg BD-QID.  Max 4g/day
Product leaflet	PO 400mg QID or 800mg BD Max: 4g/day	PO 1-2g daily in divided doses Severe infections:  4g daily in divided doses Duration of treatment: URTI: 5-10 days

Erythromycin stearate

• Previously healthy with no risk factors for drug-resistant S. pneumoniae
• Erythromycin base (stearate) (250 mg every six hours, 333 mg every eight hours, or 500 mg every 12 hours may double dose for serious infections
• but twice-daily dosing not recommended for total daily dose over 1000 mg

Erythromycin ethyl succinate

• Erythromycin ethyl succinate is available in 400 mg tablets, and two strengths of liquid formulation - 200 mg/5 mL and 400 mg/5 mL.
• The usual adult dose is 400 mg, four times daily. Alternatively, 800 mg, twice daily, may be a more convenient dose regimen for some patients. In severe infections, the dose may be increased up to a maximum of 4 g per day.
• Tablets may be taken with or without food

Pharmacokinetics

• The time peak serum erythromycin concentrations are reached varies depending on the salt. 
• A single dose of erythromycin ethylsuccinate 400mg reaches approximately 0.8mcg/ml at 1 hour whereas a single dose of erythromycin stearate 250mg reaches approximately 0.8mcg/ml at 3 hours. 
• Several references state that in general, oral administration of 250 mg of erythromycin as the base, estolate, or stearate, or 400 mg of erythromycin as the ethylsuccinate, 4 times daily maintains antibacterial serum concentrations of 0.1-2 mcg/mL

References:

1. Outpatient Treatment of Community-Acquired Pneumonia in Adults. Prescriber's Letter 2013; 29(12):291224
2. http://www.bpac.org.nz/BPJ/2012/may/macrolides.aspx
3. https://nzpharmacy.wordpress.com/2009/02/09/dose-conversions-of-erythromycin-salts/
4. www.lexicomp.com