What diseases is erythromycin a drug of choice for?

Erythromycin as Drug of Choice

Erythromycin is the drug of choice for pertussis (whooping cough) in patients who cannot tolerate azithromycin, Legionnaires' disease in outpatients, and as an alternative agent for chlamydial infections and streptococcal pharyngitis in penicillin-allergic patients. 1

Primary Indications Where Erythromycin Remains Drug of Choice

Pertussis (Whooping Cough)

• Erythromycin is effective in eliminating Bordetella pertussis from the nasopharynx and rendering patients noninfectious, though azithromycin is now preferred as first-line therapy due to better tolerability 1, 2
• When azithromycin is unavailable, erythromycin dosing is 40-50 mg/kg per day in 4 divided doses for 14 days in children, and 2 g per day in 4 divided doses for 14 days in adults 2
• Critical caveat: Erythromycin should be avoided in infants <1 month due to association with infantile hypertrophic pyloric stenosis (IHPS), with azithromycin strongly preferred in this age group 2, 3

Legionnaires' Disease

• For outpatients with Legionnaires' disease, erythromycin is an acceptable first-line option alongside azithromycin, doxycycline, clarithromycin, or fluoroquinolones 2
• Erythromycin has been historically the most commonly used drug for Legionnaires' disease, though newer agents like fluoroquinolones now show superior activity 4
• Treatment should be initiated as rapidly as feasible when epidemiologic evidence suggests legionellosis 2

Chlamydial Infections (Alternative Agent)

• Erythromycin serves as an alternative regimen for chlamydial infections when first-line agents (azithromycin or doxycycline) are contraindicated 2
• Dosing: Erythromycin base 500 mg orally four times daily for 7 days, or erythromycin ethylsuccinate 800 mg orally four times daily for 7 days 2
• Important limitation: Erythromycin is less efficacious than azithromycin or doxycycline, and gastrointestinal side effects frequently discourage compliance 2
• A test of cure should be considered 3 weeks after completion of erythromycin therapy 2

Streptococcal Pharyngitis in Penicillin-Allergic Patients

• Erythromycin is indicated for treatment of group A beta-hemolytic streptococcal pharyngitis in penicillin-allergic patients 1, 5
• The therapeutic dose should be administered for 10 days to prevent rheumatic fever 1
• Erythromycin is also recommended for long-term prophylaxis of streptococcal pharyngitis in patients allergic to both penicillin and sulfonamides to prevent recurrent rheumatic fever 1

Additional Clinical Uses

Respiratory Tract Infections

• Erythromycin is among the drugs of choice for empiric treatment of community-acquired pneumonia in outpatients, particularly for infections caused by Mycoplasma pneumoniae or Streptococcus pneumoniae 6, 7
• Effective for bronchitis and pneumonitis of mild to moderate severity 1

Skin and Soft Tissue Infections

• Indicated for mild to moderate infections caused by Streptococcus pyogenes or Staphylococcus aureus, though resistant staphylococci may emerge during treatment 1
• Drug of choice for acne and erythrasma (caused by Corynebacterium minutissimum) 6, 1

Other Specific Infections

• Diphtheria: As adjunct to antitoxin for Corynebacterium diphtheriae infections and to eradicate carriers 1
• Listeriosis: Caused by Listeria monocytogenes 1
• Intestinal amebiasis: Caused by Entamoeba histolytica (oral forms only) 1
• Campylobacter enteritis 6

Critical Safety Considerations and Drug Interactions

Infantile Hypertrophic Pyloric Stenosis (IHPS)

• Erythromycin carries significant risk of IHPS in neonates, with one study showing 7 cases out of 157 exposed infants versus zero in unexposed infants 2
• Parents must be counseled about signs of IHPS when erythromycin is prescribed to newborns 2

Cardiovascular Risks

• Erythromycin is contraindicated with astemizole, cisapride, pimazole, or terfenadine due to risk of QT prolongation, cardiac arrest, torsades de pointes, and ventricular arrhythmias 2, 3

Cytochrome P450 Interactions

• Erythromycin inhibits CYP3A enzymes, causing numerous drug interactions with alfentanil, bromocriptine, cyclosporine, carbamazepine, statins, benzodiazepines, sildenafil, digoxin, theophylline, warfarin, and many others 2, 3

Gastrointestinal Side Effects

• Dose-related gastrointestinal irritation (epigastric distress, abdominal cramps, nausea, vomiting, diarrhea) is the most common adverse effect, occurring more frequently than with azithromycin 2, 3
• In one outbreak study, 76% of patients who discontinued erythromycin cited side effects, with 91% reporting gastrointestinal upset 8
• Enteric-coated formulations and ester derivatives can be taken with food to minimize these effects 2

Comparative Efficacy and Modern Alternatives

While erythromycin remains effective for its traditional indications, newer macrolides (azithromycin, clarithromycin) and fluoroquinolones have largely supplanted it as first-line therapy due to superior tolerability, shorter treatment courses, and better compliance 2, 8. Erythromycin now primarily serves as an alternative when preferred agents are unavailable or contraindicated.