Azithromycin Dosing for Adults
Standard Dosing Regimens
For most common infections in adults with normal renal and hepatic function, azithromycin is dosed as 500 mg on day 1, followed by 250 mg once daily on days 2-5 (the standard "Z-pack" regimen), or as a single 1 gram dose for specific infections like chlamydia. 1
Infection-Specific Dosing
Respiratory Tract Infections:
- Community-acquired pneumonia (CAP): 500 mg IV or oral daily for 2-5 days, then 500 mg oral daily to complete 7-10 days total 1
- Acute bacterial sinusitis: Single 2 gram dose (extended-release formulation) 2
- Atypical pneumonia: 500 mg once daily for 3 days (total 1.5 g) 3
Sexually Transmitted Infections:
- Non-gonococcal urethritis/cervicitis (chlamydia): Single 1 gram oral dose 1
Skin and Soft Tissue Infections:
- Uncomplicated infections: 500 mg once daily for 3 days 4
Cat Scratch Disease:
- Patients >45 kg: 500 mg on day 1, then 250 mg daily for 4 additional days 1
Mycobacterial Infections:
- Disseminated MAC disease: 250 mg daily with ethambutol, with or without rifabutin 1
- MAC prophylaxis (AIDS, CD4 <50): 1,200 mg once weekly 1
- Non-tuberculous mycobacterial infections: 250-500 mg daily (not as a 3-day course) 5
Chronic Respiratory Conditions (Long-term Prophylaxis):
- Bronchiectasis with ≥3 exacerbations/year: 500 mg three times weekly OR 250 mg daily 1
- Minimum 6-12 months duration required to demonstrate benefit 1
- Bronchiolitis obliterans syndrome (lung transplant): 250 mg daily for 5 days, then 250 mg three times weekly for at least 3 months 1
Administration Considerations
Timing and Food:
- Can be taken with or without food 6
- However, coadministration with a large meal may reduce absorption by up to 50% 7
Drug Interactions:
- Avoid concurrent aluminum- or magnesium-containing antacids, which reduce absorption by up to 50% 6, 5
- Separate antacid administration by at least 2 hours 6
- Cimetidine does not affect azithromycin absorption 8
Special Populations
Renal Insufficiency:
- No dose adjustment needed for mild-to-moderate renal impairment (GFR 10-80 mL/min) 8
- Severe renal impairment (GFR <10 mL/min) increases Cmax by 61% and AUC by 35%, but specific dosing adjustments are not well-established 8
- Standard doses are generally used in clinical practice for patients with normal to moderate renal dysfunction 9
Hepatic Insufficiency:
- Pharmacokinetics have not been established in hepatic impairment 8
- Use with caution and increase monitoring if underlying liver disease present 9
Safety Monitoring and Precautions
Cardiac Considerations:
- Obtain baseline ECG before long-term therapy, particularly in elderly patients with cardiac risk factors 1
- Contraindicated if QTc >450 ms (men) or >470 ms (women) 1
- Avoid in patients taking other QT-prolonging medications without careful risk assessment 1
Laboratory Monitoring:
- Baseline liver function tests recommended for long-term therapy 1
- Routine uric acid measurements not needed 9
Common Adverse Effects:
- Gastrointestinal symptoms (nausea, diarrhea, abdominal pain, vomiting) are most common but generally mild to moderate 6, 5, 1
- Better GI tolerance than erythromycin 7
- Dizziness and headache may occur 5
Clinical Pearls and Pitfalls
Advantages:
- Extensive tissue distribution with concentrations exceeding serum levels by up to 100-fold 8, 10
- Prolonged terminal half-life of 68 hours allows for short-course or single-dose therapy 8
- Once-daily dosing significantly improves adherence compared to alternatives 1
Critical Caveats:
- 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
- For sexually transmitted infections, patients should abstain from intercourse for 7 days after completing therapy 1
- Dispense medication on-site when possible to maximize compliance 1