Erythromycin Dosing for Chlamydia and Other Infections: Clinical Reference

Base: Acid-labile; take empty stomach (or with food if GI upset).
Estolate: Better absorption; contraindicated in pregnancy (hepatotoxicity).
Ethylsuccinate / stearate: Acid-stable; take with food.
Delayed-release (Ery-Tab): BID dosing.

Erythromycin is a macrolide antibiotic with specific indications and regimens. Below are evidence-based dosages for key infections.

Chlamydia trachomatis Infections

Uncomplicated urogenital/rectal (adults): Erythromycin base 500 mg PO QID × 7 days OR Ethylsuccinate 800 mg PO QID × 7 days OR Erythromycin base delayed-release 500 mg PO BID × 7 days.
Pregnancy: Azithromycin 1 g PO single dose preferred; if macrolide needed → erythromycin base 500 mg PO QID × 7 days (estolate contraindicated in pregnancy).
Neonatal conjunctivitis/pneumonia: Erythromycin base/ethylsuccinate 50 mg/kg/day PO ÷ QID × 14 days.

Legionnaires' disease: Azithromycin/fluoroquinolone preferred; if erythromycin: IV 0.5–1 g q6h → PO 500 mg QID × 14–21 days.
Pertussis: Azithromycin preferred; erythromycin 40–50 mg/kg/day ÷ QID × 14 days (infants: risk of IHPS).
Campylobacter enteritis: Azithromycin preferred; erythromycin 500 mg QID × 3–5 days.
Diphtheria (adjunct): Erythromycin/penicillin + antitoxin.
Syphilis (penicillin-allergic, non-pregnant): Doxycycline preferred; erythromycin less reliable.
Mycobacterium avium complex (MAC) prophylaxis (HIV, CD4 <50): Azithromycin/clarithromycin preferred; erythromycin 500 mg PO BID + rifabutin (alternative).

GI: Nausea, vomiting, cramps, diarrhea (motilin agonist).
QT prolongation → Torsades (avoid with other QT drugs).
CYP3A4 inhibition → ↑ levels of statins, calcium channel blockers, DOACs, tacrolimus, etc.
Infantile hypertrophic pyloric stenosis (IHPS) risk in neonates <2 weeks.

Azithromycin and doxycycline are now preferred for most chlamydia indications due to tolerability and adherence.