What is the recommended dose of azithromycin for a typical adult patient with no significant medical history?

Azithromycin Dosing for Adults

For a typical adult patient with no significant medical history, the standard azithromycin regimen is 500 mg on day 1, followed by 250 mg once daily on days 2 through 5 (the "Z-pack"), providing a total dose of 1.5 grams over 5 days. 1, 2

Standard Dosing Regimens by Indication

Respiratory Tract Infections

• Community-acquired pneumonia, acute bacterial sinusitis, and bronchitis: 500 mg on day 1, then 250 mg daily on days 2-5 1, 2
• Alternative 3-day regimen: 500 mg once daily for 3 consecutive days provides the same total 1.5 gram dose and demonstrates equivalent efficacy 1, 3
• Both regimens achieve comparable serum and tissue exposures, with the 3-day course offering improved compliance 2, 3

Sexually Transmitted Infections

• Non-gonococcal urethritis and cervicitis (Chlamydia trachomatis): Single 1 gram oral dose 1, 4, 5
• This single-dose regimen provides therapeutic tissue concentrations for approximately 10 days due to azithromycin's prolonged tissue half-life 5, 2
• Critical advantage: Allows for directly observed therapy and maximizes adherence in populations with erratic healthcare-seeking behavior 1, 5

Important Contraindication

• Do NOT use azithromycin as monotherapy for gonococcal infections due to widespread resistance; must combine with ceftriaxone if gonorrhea is suspected 1, 4

Administration Considerations

Timing and Food Interactions

• Azithromycin can be taken with or without food, though food increases Cmax by 23-56% without affecting overall absorption (AUC) 2
• Separate from antacids by at least 2 hours: Aluminum- or magnesium-containing antacids reduce absorption by up to 50% 1, 4, 2

Bioavailability and Tissue Distribution

• Oral bioavailability is 37-38% 2
• Tissue concentrations exceed serum concentrations by up to 100-fold, with extensive intracellular accumulation in phagocytes 6
• Terminal elimination half-life is 68 hours, allowing for once-daily dosing and prolonged therapeutic effect after treatment completion 2, 6

Safety Monitoring and Precautions

Cardiac Screening

• Obtain baseline ECG in patients with cardiac risk factors before initiating therapy 1
• Contraindication: QTc >450 ms (men) or >470 ms (women) 7, 1, 5
• Avoid in patients taking other QT-prolonging medications or with history of heart disease, low potassium, slow pulse, family history of sudden death, or known prolonged QT interval 7

Common Adverse Effects

• Gastrointestinal symptoms (nausea, vomiting, abdominal pain, diarrhea) are the most common side effects, though less frequent than with erythromycin 1, 5, 2
• Headache and dizziness may occur but are generally mild to moderate 1, 5

Special Populations

• Pregnancy: Category B; considered safe and preferred over erythromycin in infants <1 month due to lower risk of infantile hypertrophic pyloric stenosis 1, 4, 5
• Renal impairment: Standard doses are generally used in normal to moderate renal dysfunction 5, 2
• Severe renal impairment (GFR <10 mL/min): Exercise caution as AUC increases by 35% and Cmax by 61% 5, 2
• Hepatic impairment: Use with caution and increase monitoring if underlying liver disease is present 5

Common Pitfalls to Avoid

• Do NOT use azithromycin as first-line for streptococcal pharyngitis due to increasing macrolide resistance in group A Streptococcus; reserve as alternative only in penicillin-allergic patients 1
• Verify liquid formulation concentration before calculating mL dose, as concentrations vary (200 mg/5 mL vs 100 mg/5 mL) 4
• For sexually transmitted infections, counsel patients to abstain from sexual intercourse for 7 days after completing therapy to prevent transmission 5
• Dispense medication on-site when possible and directly observe the first dose to maximize adherence 1, 5