Dose conversions of erythromycin saltsFiled under: Pharmacy Practice — Leave a comment

February 9, 2009

Martindale says that each 1 g of erythromycin is equivalent to about the following amounts of each salt or ester:

erythromycin estolate 1.44 g

erythromycin ethyl succinate 1.17 g

erythromycin gluceptate 1.31 g

erythromycin lactobionate 1.49 g

erythromycin propionate 1.08 g

erythromycin stearate 1.39 g

Reading this could be taken to mean that 1.39g of stearate is therefore equivalent to 1.17g of ethylsuccinate.  So if

250mg of stearate was prescribed and you didn’t have it, you might say “I’ll give 210mg of ethylsuccinate instead (ie.

if you could), because it provides the same ‘dose’ of base erythromycin”.

Erythromycin may be administered as the base or its salts or esters and doses of erythromycin are expressed in terms

of the base, that is:

- ERA 250mg tablets contains erythromycin stearate equivalent to 250mg of erythromycin base.

- E-Mycin 400mg contains erythromycin ethyl succinate equivalent to 400mg of erythromycin base.

The strengths expressed on the labels of the dispensary stock are those of the base.

Therefore you don’t need to go through the conversion calculation above.

HOWEVER, the bioavailability of erythromycin is variable and depends on several factors including the particular

derivative, the formulation of the dosage form administered, acid stability of the derivative (which varies), presence of

food in the GI tract and gastric emptying time.  This is further reasoning why the “conversion” above is irrelevant. 

What is relevant is how much erythromycin is absorbed systemically, and how this compares between the salts/esters.

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

The usual adult oral dose is the equivalent of 1- 2 gram of erythromycin base daily, given in 2 to 4 divided doses and

for severe infections this may be increased up to 4gram daily.

A short half life (1-1.5 hours) means dosing four times daily is generally required.

- The recommended adult dose of the ethylsuccinate is 400mg every six hours (ie. 1.2gram daily) up to a maximum of

4gram per day in severe infections.

- The recommended adult dose of the stearate is 250mg every six hours or 500mg every 12 hours (ie 1 gram daily) up

to a maximum of 4gram per day in severe infections.

** So, the breakdown and absorption of these salts differ such that clinically, 250mg of ERA (erythromycin

stearate) is considered comparable to a dose of 400mg of E-Mycin (erythromycin ethyl succinate).

Thanks to Bob Buckham, Dave Woods, Jocelyn Livesey (Dunedin MI), and Pam Buffery (Christchurch DI) for their

assistance with interpreting the information around this.

References –

Martindale 34th edition 2005, p210

AHFS Drug Information (2008), p229

BNF 56th edition Sept 2008, p305

AUS DI, p968

Handbook of Clinical Drug Data 10th edition 2002, p164

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The pharmacokinetics and tolerance of oral erythromycin stearate compared with erythromycin ethylsuccinate: implications for preventing endocarditis

1. D. C. Shanson*, 2. P. Tidbury*, 3. W. R. McNabb† and 4. M. Tadayon*

+Author Affiliations1. *Departments of Clinical Microbiology, St. Stephen's Hospital and Westminster Medical

School Fulham Road, London S.W.10, England2. †Departments of Therapeutics, St. Stephen's Hospital and Westminster Medical

School Fulham Road, London S. W.10, England Accepted March 27, 1984.

Abstract

Serum concentrations of erythromycin were monitored in 11 healthy adult volunteers following single dose oral administration of erythromycin stearate, 1.5 g, and erythromycin ethylsuccinate 3·0 g. Peak serum concentrations occurred at 30 min to 2 h after the dose, usually at 1 h. Mean serum peak erythromycin concentrations (standard deviation) were 4·8 mg/l (±2·0) following 1·5 g erythromycin stearate and 2·8 mg/l (±1·4) after 3·0 g erythromycin ethylsuccinate. Both types of erythromycin frequently caused mild gastrointestinal side-effects but there were fewer side-effects associated with erythromycin ethylsuccinate. However, because of the increased serum erythromycin concentrations between 1 and 6 h after the dose of the stearate preparation compared to ethylsuccinate we recommend erythromycin stearate, 1·5 g, as the preferred loading dose, given 1 h before the dental procedure, for preventing endocarditis in susceptible patients allergic to penicillin.

© 1984 The British Society for Antimicrobial Chemotherapy

Absorption of erythromycin from pediatric suspension in infants and children.Eriksson M, Bolme P, Blennow M.

AbstractThe absorption of erythromycin in infants and children was estimated after the administration of an erythromycin suspension. The subjects were divided into 3 age groups: 0-1 month, 1-6 months and 6 months-6 years. The absorption was lower in infants less than 1 month of age than in the older children. Erythromycin ethylsuccinate and erythromycin stearate were equally well absorbed in the fasting state in subjects 6 months-6 years of age. Administration of the drug at mealtimes considerably increased the absorption of erythromycin ethylsuccinate but had little effect on the absorption of erythromycin stearate. The absorption of erythromycin stearate in the fasting state was much lower than that of erythromycin ethylsuccinate in infants 1-6 months of age. None of the infants given erythromycin ethylsuccinate because of an outbreak of whooping-cough on the neonatal ward showed evidence of liver toxicity, nor did they develop symptoms of whooping-cough.

PMID:

 

7313575

 

[PubMed - indexed for MEDLINE]