What is the recommended dose of Zithromax (azithromycin) for bacterial infections?

Azithromycin (Z-Pak) Dosing

For most bacterial infections in adults, azithromycin is dosed as 500 mg on day 1, followed by 250 mg once daily on days 2-5 (total 1.5 g over 5 days), or alternatively 500 mg once daily for 3 days. 1

Standard Adult Dosing Regimens

Respiratory Tract Infections

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

Skin and Soft Tissue Infections

• Uncomplicated skin/skin structure infections: 500 mg on day 1, then 250 mg daily on days 2-5 1

Sexually Transmitted Infections

• Non-gonococcal urethritis and cervicitis: Single 1 gram dose 1
• Chancroid (genital ulcer disease): Single 1 gram dose 1
• Gonococcal urethritis and cervicitis: Single 2 gram dose 1

Pediatric Dosing (Age ≥6 months)

Acute Otitis Media

Three dosing options are available 1:

• Single-dose regimen: 30 mg/kg as a single dose
• 3-day regimen: 10 mg/kg once daily for 3 days
• 5-day regimen: 10 mg/kg on day 1, then 5 mg/kg daily on days 2-5

Community-Acquired Pneumonia

• 5-day regimen: 10 mg/kg on day 1, then 5 mg/kg daily on days 2-5 1

Acute Bacterial Sinusitis

• 3-day regimen: 10 mg/kg once daily for 3 days 1

Pharyngitis/Tonsillitis (Age ≥2 years)

• 5-day regimen: 12 mg/kg once daily for 5 days 1

Atypical Pathogen Coverage

Mycoplasma pneumoniae

• Pediatric intravenous: 10 mg/kg on days 1 and 2, then transition to oral 2
• Pediatric oral: 10 mg/kg on day 1, then 5 mg/kg daily on days 2-5 2

Chlamydia trachomatis or Chlamydophila pneumoniae

• Pediatric dosing: Same as Mycoplasma (10 mg/kg day 1, then 5 mg/kg daily days 2-5) 2

Legionnaires' Disease

• Hospitalized patients: 500 mg IV daily for 2-7 days, then oral to complete 7-10 days total 3
• Non-hospitalized mild disease: 500 mg on day 1, then 250 mg daily for 4 additional days 3

Special Populations

Renal Impairment

• No dosage adjustment needed for GFR 10-80 mL/min 1
• Use with caution in severe renal impairment (GFR <10 mL/min), as AUC increases by 35% 1

Hepatic Impairment

• No specific dosage recommendations available due to lack of pharmacokinetic data 1

Age and Gender

• No dosage adjustment required based on age or gender alone 1

Administration Considerations

• Can be taken with or without food for both tablets and oral suspension 1
• Avoid large meals when administering, as absorption may be reduced by up to 50% 4

Critical Safety Precautions

Cardiac Monitoring

• Obtain baseline ECG in patients with cardiac risk factors before initiating therapy 5
• Avoid azithromycin if QTc >450 ms (men) or >470 ms (women) 5

Common Pitfalls

• Gastrointestinal side effects (nausea, diarrhea, abdominal pain) occur in approximately 3-6% of patients 5, 6
• Resistance concerns: Macrolide resistance varies geographically and temporally, particularly for group A streptococcus 2
• Not first-line for strep pharyngitis: Only use as alternative in penicillin-allergic patients 2

Antimicrobial Stewardship

• Limit antibiotic exposure whenever possible to minimize resistance development 5
• Consider viral etiology before prescribing for respiratory infections 5
• Use shortest effective duration to minimize antimicrobial exposure 5
• Assess clinical response at days 5-7 for improvement of symptoms 5

Evidence for Dosing Flexibility

Research demonstrates that the total 1.5 g dose is equally effective whether given over 3 days (500 mg daily) or 5 days (500 mg day 1, then 250 mg daily), due to azithromycin's unique pharmacokinetics with prolonged tissue concentrations 7, 8, 9. Tissue concentrations remain above MIC for key pathogens for up to 10 days after completion of therapy 7.