Erythromycin Dosage for a 13-Year-Old
For a 13-year-old patient, the recommended erythromycin dosage is 40-50 mg/kg/day divided into 4 doses (maximum 2 g/day), administered for 14 days for most indications. 1
Standard Dosing Regimen
The FDA-approved dosage for children is 30-50 mg/kg/day in equally divided doses, with the ability to double this for severe infections (not exceeding 4 g/day). 2
For a 13-year-old, the practical dosing is typically 500 mg four times daily (every 6 hours), which falls within the 40-50 mg/kg/day range for an average-weight adolescent. 1, 2
The duration of therapy should be 14 days for most bacterial infections, as shorter courses (7-10 days) have been associated with relapses. 1
Indication-Specific Considerations
Pertussis (Whooping Cough)
- For pertussis treatment or post-exposure prophylaxis, use 40-50 mg/kg/day in 4 divided doses (maximum 2 g/day) for 14 days. 1
Streptococcal Pharyngitis
- For strep throat, administer the standard dose for at least 10 days to prevent rheumatic fever complications. 2
- Note that penicillin remains first-line; erythromycin is reserved for penicillin-allergic patients. 3
Community-Acquired Pneumonia
- For pneumonia in adolescents, the British Thoracic Society recommends 500 mg four times daily for 7-10 days (may extend to 14 days based on clinical response). 1
Important Clinical Considerations
Gastrointestinal Side Effects
- Erythromycin causes significantly more gastrointestinal side effects (nausea, vomiting, abdominal cramps, diarrhea) compared to other macrolides like azithromycin. 1
- These symptoms are dose-related and can be minimized by using enteric-coated formulations or taking with food (though optimal absorption occurs on an empty stomach). 1, 2
Drug Interactions
- Never administer erythromycin with astemizole, cisapride, pimozide, or terfenadine due to serious cardiac arrhythmia risk. 1
- Monitor patients carefully when combining with drugs metabolized by cytochrome P450 enzymes. 1
Alternative Macrolide Options
- Consider azithromycin (500 mg day 1, then 250 mg days 2-5) or clarithromycin (250 mg twice daily for 7-10 days) as alternatives with better tolerability profiles and more convenient dosing. 1
- Azithromycin has fewer gastrointestinal side effects and requires only once-daily dosing, improving adherence in adolescents. 1
Common Pitfalls to Avoid
- Do not prescribe courses shorter than 14 days for pertussis or other serious infections, as relapse rates increase. 1
- Avoid erythromycin as first-line for typical bacterial pneumonia caused by S. pneumoniae or H. influenzae; beta-lactams (amoxicillin) remain preferred. 1
- Do not use erythromycin in infants under 1 month due to infantile hypertrophic pyloric stenosis (IHPS) risk; azithromycin is preferred in this age group. 1