What is the recommended dosing for azithromycin (Zithromax)?

Azithromycin (Zithromax) Dosing Guidelines

The recommended standard dosing regimen for azithromycin (Zithromax) in adults is 500 mg on day 1, followed by 250 mg once daily on days 2 through 5 for most common infections. 1

Adult Dosing Regimens by Indication

Standard 5-Day Regimen

• Community-acquired pneumonia (mild severity)
• Pharyngitis/tonsillitis (second-line therapy)
• Skin/skin structure infections (uncomplicated)
  • 500 mg as a single dose on day 1, followed by 250 mg once daily on days 2-5 1

3-Day Regimen

• Acute bacterial exacerbations of COPD (mild to moderate)
• Acute bacterial sinusitis
  • 500 mg once daily for 3 days 1
  • Alternative for COPD: 500 mg on day 1, followed by 250 mg once daily on days 2-5 1

Single-Dose Regimens

• Genital ulcer disease (chancroid): One single 1-gram dose 1
• Non-gonococcal urethritis and cervicitis: One single 1-gram dose 1
• Gonococcal urethritis and cervicitis: One single 2-gram dose 1

Special Indications

Cat Scratch Disease

• Patients >45 kg: 500 mg on day 1 followed by 250 mg for 4 additional days 2
• Patients <45 kg: 10 mg/kg on day 1 and 5 mg/kg for 4 more days 2

Babesiosis

• In combination with atovaquone:
  • Adults: 500-1000 mg on day 1, then 250 mg once daily thereafter 2
  • Immunocompromised patients: 600-1000 mg per day 2

Bronchiectasis (to reduce exacerbations)

• 500 mg three times a week or 250 mg daily for a minimum of 6 months 2
• A starting dose of 250 mg three times a week may be used to minimize side effects 2

Pediatric Dosing

Acute Otitis Media

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

Acute Bacterial Sinusitis

• 10 mg/kg once daily for 3 days 1

Community-Acquired Pneumonia

• 10 mg/kg on day 1, followed by 5 mg/kg on days 2-5 1

Pharyngitis/Tonsillitis

• 12 mg/kg once daily for 5 days 1

Administration Considerations

• Azithromycin tablets can be taken with or without food 1
• Do not take with aluminum or magnesium-containing antacids simultaneously 3
• Take at least 2 hours before or after antacids 3

Special Populations

Renal Impairment

• No dosage adjustment needed for GFR 10-80 mL/min 1
• Use caution in severe renal impairment (GFR <10 mL/min) 1

Hepatic Impairment

• No specific dose recommendations available for hepatic impairment 1

Pregnancy

• Alternative regimen for chlamydial infection: 1 g orally in a single dose 2
• Safety data in pregnancy is limited but preliminary data indicate it may be safe 2

Side Effects and Monitoring

• Most common side effects: gastrointestinal disturbances (diarrhea, abdominal pain), headache, dizziness 3, 4
• ECG should be performed prior to initiation of long-term therapy to assess QTc interval 2
• Long-term use may lead to increased antimicrobial resistance 2

Clinical Pearls

• Azithromycin has excellent tissue penetration and intracellular accumulation, allowing for once-daily dosing and shorter treatment courses 4
• The 3-day regimen (500 mg daily) provides equivalent efficacy to the 5-day regimen for many indications 5
• Azithromycin has a long half-life (up to 5 days), which contributes to its extended antimicrobial effect even after completing the dosing regimen 4
• For travelers' diarrhea, azithromycin is preferred over fluoroquinolones in areas with high rates of fluoroquinolone resistance 2

Remember that while these are standard dosing recommendations, clinical judgment should be used based on severity of infection, patient characteristics, and local resistance patterns.