Z-Pak (Azithromycin) Dosing
The standard "Z-Pak" regimen is 500 mg on day 1, followed by 250 mg once daily on days 2 through 5, for a total 5-day course. 1, 2
Adult Dosing by Indication
Respiratory Tract Infections
- Community-acquired pneumonia, bronchitis, sinusitis: 500 mg on day 1, then 250 mg daily on days 2-5 (standard Z-Pak) 1, 2
- Alternative 3-day regimen: 500 mg once daily for 3 days is also effective for respiratory infections 3
- Both regimens maintain therapeutic tissue concentrations for up to 10 days after the last dose due to azithromycin's prolonged tissue half-life 4, 5
Sexually Transmitted Infections
- Chlamydial urethritis/cervicitis: Single 1 gram oral dose 6, 1, 7
- This single-dose regimen provides therapeutic urogenital tissue concentrations for approximately 10 days 4
- Critical advantage: Directly observed therapy improves compliance in populations unlikely to return for follow-up 1
Streptococcal Pharyngitis/Tonsillitis
- 12 mg/kg once daily for 5 days (maximum 500 mg/day) 2
- Azithromycin is NOT first-line for strep throat—reserve for penicillin-allergic patients only 8
- The higher dose (12 mg/kg vs. 10 mg/kg) is necessary to prevent recurrence 9
Long-Term Prophylactic Regimens
- Bronchiectasis with ≥3 exacerbations/year: 500 mg three times weekly for at least 6 months 1
- Alternative: 250 mg daily also has strong evidence 1
- Obtain baseline ECG (contraindicated if QTc >450 ms in men or >470 ms in women) and liver function tests before starting 1
Pediatric Dosing (Age ≥6 months)
Respiratory Infections
- Otitis media, community-acquired pneumonia: 10 mg/kg on day 1, then 5 mg/kg daily on days 2-5 2, 9
- Alternative for otitis media: Single 30 mg/kg dose 2
- Acute bacterial sinusitis: 10 mg/kg once daily for 3 days 2
Pharyngitis/Tonsillitis (Age ≥2 years)
- 12 mg/kg once daily for 5 days (maximum 500 mg/day) 2
- Higher dose required to match penicillin efficacy and prevent recurrence 9
Administration Considerations
Timing and Food
- Can be taken with or without food 2
- Avoid concurrent antacids: Aluminum or magnesium-containing antacids reduce absorption by up to 50%—separate by ≥2 hours 1, 8
Compliance Strategies
- Dispense medication on-site when possible 1
- Directly observe first dose, especially for single-dose regimens 1
- Single-dose and once-daily regimens significantly improve adherence compared to multiple-daily-dosing alternatives 1, 3
Common Pitfalls and Precautions
Adverse Effects
- Gastrointestinal symptoms (diarrhea, nausea, abdominal pain, vomiting) are most common but less frequent than with erythromycin 1, 9
- Generally mild to moderate in severity 9
Resistance and Inappropriate Use
- Never use as monotherapy for gonorrhea due to widespread resistance—must combine with ceftriaxone if gonococcal infection suspected 1
- Long-term use increases antimicrobial resistance risk 1
Cardiac Considerations
- Avoid in patients with prolonged QTc or those taking other QT-prolonging medications without careful risk assessment 1
- Mandatory ECG screening before long-term therapy 1
Sexual Transmission Prevention
- Patients treated for STIs must abstain from sexual intercourse for 7 days after completing therapy 1
- Treat sex partners to prevent reinfection 6