What is the recommended azithromycin (Zithromax) dose for treating uncomplicated Chlamydia trachomatis infection in a healthy adult and in children weighing less than 50 kg?

Azithromycin (Zithromax) Dosing for Chlamydia

For uncomplicated chlamydia in healthy adults, give azithromycin 1 g orally as a single dose; for children weighing less than 45 kg, use erythromycin base or ethylsuccinate 50 mg/kg/day divided into four doses daily for 14 days. 1, 2

Adult Dosing (≥45 kg)

Azithromycin 1 g orally as a single dose is the recommended first-line treatment for uncomplicated genital chlamydia in adults. 1, 2, 3 This regimen achieves cure rates of 97-98% and is equally effective as doxycycline 100 mg twice daily for 7 days. 1, 2, 4

Key Advantages of Single-Dose Azithromycin

• Directly observed therapy is possible, eliminating compliance concerns that plague multi-day regimens. 1, 3
• Preferred when follow-up is unpredictable or in populations with erratic health-care-seeking behavior. 1, 3
• Medication should be dispensed on-site with the first dose observed to maximize compliance. 1

Clinical Efficacy Data

The single 1 g dose has been validated in multiple controlled trials showing 96-97% bacteriologic cure rates at follow-up. 5, 6, 4, 7 Treatment failures are predominantly reinfections from untreated partners rather than true antibiotic resistance. 3, 5

Pediatric Dosing

Children ≥8 Years Weighing >45 kg

Use adult dosing: azithromycin 1 g orally as a single dose. 1, 2, 3 Alternatively, doxycycline 100 mg orally twice daily for 7 days may be used in this age/weight group. 1, 2

Children <45 kg (Critical Weight Cutoff)

Do NOT use azithromycin 1 g in children under 45 kg. Instead, use erythromycin base or ethylsuccinate 50 mg/kg/day orally divided into four doses daily for 14 days. 1, 2, 3 This weight-based dosing is essential because the standard adult dose is inappropriate for smaller children.

Special Population: Pregnancy

Azithromycin 1 g orally as a single dose is the preferred treatment during pregnancy. 1, 2, 3 Doxycycline and all fluoroquinolones are absolutely contraindicated due to teratogenic risk. 1, 2

• Amoxicillin 500 mg orally three times daily for 7 days is an acceptable alternative if azithromycin cannot be used. 1, 2
• Mandatory test-of-cure 3-4 weeks after treatment completion is required for all pregnant patients, unlike non-pregnant adults. 1, 2

Critical Management Requirements

Sexual Abstinence

Patients must abstain from all sexual intercourse for 7 days after taking the single dose and until all sex partners have completed treatment. 1, 2, 3 This is non-negotiable to prevent reinfection.

Partner Management

All sex partners from the preceding 60 days must be evaluated, tested, and empirically treated with the same regimen, even if asymptomatic. 1, 2, 3 Failure to treat partners leads to reinfection in up to 20% of cases. 2, 3

Follow-Up Testing

• Test-of-cure is NOT recommended for non-pregnant patients treated with azithromycin who are asymptomatic, as cure rates exceed 97%. 1, 2, 3
• All women should be retested at 3 months to screen for reinfection, which occurs in up to 39% of adolescent populations and increases risk of pelvic inflammatory disease. 1, 2, 3
• Do not test before 3 weeks post-treatment, as nucleic acid amplification tests can yield false-positives from residual dead organisms. 1, 3

Common Pitfalls to Avoid

• Do not assume treatment failure when recurrence occurs—84-92% of recurrent infections are reinfections from untreated partners, not antibiotic resistance. 3
• Do not use the 1 g dose in children <45 kg—this is a critical weight cutoff requiring different dosing. 1, 2
• Do not skip partner treatment—both patient and all partners must complete therapy before resuming intercourse. 1, 2, 3
• Do not omit the 3-month retest in women—this is when reinfection risk peaks and PID risk is elevated. 1, 2, 3