What is the typical dosage and treatment duration of a Z (azithromycin) pack for bacterial infections?

Z-Pack (Azithromycin) Dosing and Duration

The standard Z-pack regimen is 500 mg on day 1, followed by 250 mg once daily on days 2-5 (total 1.5g over 5 days) for most respiratory tract infections, though specific conditions may require alternative dosing. 1

FDA-Approved Dosing Regimens

Respiratory Tract Infections

• Community-acquired pneumonia (mild): 500 mg day 1, then 250 mg daily days 2-5 1
• Pharyngitis/tonsillitis (second-line): 500 mg day 1, then 250 mg daily days 2-5 1
• Acute bacterial sinusitis: 500 mg once daily for 3 days 1
• COPD exacerbations: Either 500 mg daily for 3 days OR 500 mg day 1, then 250 mg daily days 2-5 1

Alternative 3-Day Regimen

• 500 mg once daily for 3 consecutive days is an acceptable alternative for sinusitis and COPD exacerbations, providing the same total dose of 1.5g 1, 2

Skin and Sexually Transmitted Infections

• Uncomplicated skin infections: 500 mg day 1, then 250 mg daily days 2-5 1
• Non-gonococcal urethritis/cervicitis: Single 1-gram dose 1
• Chancroid: Single 1-gram dose 1
• Gonococcal urethritis/cervicitis: Single 2-gram dose 1

Pediatric Dosing (≥6 months)

Community-Acquired Pneumonia

• 10 mg/kg day 1 (max 500 mg), then 5 mg/kg daily days 2-5 1

Acute Otitis Media (Three Options)

• Single 30 mg/kg dose 1
• 10 mg/kg once daily for 3 days 1
• 10 mg/kg day 1, then 5 mg/kg daily days 2-5 1

Pharyngitis/Tonsillitis

• 12 mg/kg once daily for 5 days (ages ≥2 years) 1

Critical Pharmacokinetic Considerations

Azithromycin has a terminal elimination half-life of 68 hours, meaning complete drug elimination takes 14-20 days after the last dose. 3, 4 This extended half-life enables:

• Once-daily dosing convenience 3
• Shorter treatment courses compared to other antibiotics 3
• Prolonged subinhibitory concentrations that may select for resistant organisms 4, 3

Important Clinical Caveats

When NOT to Use Azithromycin Monotherapy

Azithromycin monotherapy should NOT be used for community-acquired pneumonia in patients with comorbidities (COPD, diabetes, heart failure, malignancy, age >65, recent antibiotic use within 3 months, immunosuppression) or in areas with macrolide resistance ≥25%. 2 These patients require combination therapy with a β-lactam plus azithromycin or a respiratory fluoroquinolone alone 2

Cardiac Screening

• Obtain ECG before initiating therapy in patients with cardiac risk factors 2
• Avoid if QTc >450 ms (men) or >470 ms (women) 2

Drug Interactions

• Do not administer with aluminum- or magnesium-containing antacids, as they reduce absorption by up to 50% 5, 6
• Can be taken with or without food 1

Resistance Concerns

• 20-30% of S. pneumoniae isolates show macrolide resistance, and clinical failures can occur requiring hospitalization and β-lactam therapy 2
• The prolonged subinhibitory "window" (14-20 days) may promote selection of resistant organisms 4, 3

Special Populations

Renal Impairment

• No dose adjustment needed for GFR >10 mL/min 1
• Exercise caution with GFR <10 mL/min (35% increase in AUC) 1

Hepatic Impairment

• Pharmacokinetics not established; no specific dosing recommendations available 1

Hospitalized Patients

Azithromycin monotherapy is contraindicated in hospitalized patients with pneumonia—combination therapy with a β-lactam (ampicillin-sulbactam, ceftriaxone, or cefotaxime) plus azithromycin 500 mg daily is mandatory 2