What is the recommended dosage and treatment duration of Azithromycin (macrolide antibiotic) for various bacterial infections, including community-acquired pneumonia and skin and soft tissue infections, considering Impaired renal function?

Azithromycin Dosing Guidelines for Bacterial Infections

For bacterial infections including community-acquired pneumonia and skin/soft tissue infections, azithromycin should be dosed at 500 mg on day 1 followed by 250 mg once daily for days 2-5, with dose adjustments required for severe renal impairment (GFR <10 mL/min).

Standard Adult Dosing Regimens

Community-Acquired Pneumonia (CAP)

• Standard regimen: 500 mg as a single dose on day 1, followed by 250 mg once daily on days 2-5 1
• Alternative short-course: 500 mg daily for 3 days (for mild to moderate cases) 1

Skin and Soft Tissue Infections (SSTIs)

• Standard regimen: 500 mg as a single dose on day 1, followed by 250 mg once daily on days 2-5 1
• Total treatment course of 1.5 g has shown comparable efficacy to longer courses of erythromycin or cloxacillin 2, 3

Other Infections

• Acute bacterial sinusitis: 500 mg daily for 3 days 1
• Acute bacterial exacerbations of COPD:
  • 500 mg daily for 3 days, OR
  • 500 mg on day 1, followed by 250 mg daily on days 2-5 1
• Genital ulcer disease (chancroid): Single 1 gram dose 1
• Non-gonococcal urethritis/cervicitis: Single 1 gram dose 1
• Gonococcal urethritis/cervicitis: Single 2 gram dose 1

Pediatric Dosing

Community-Acquired Pneumonia

• 10 mg/kg as a single dose on day 1, followed by 5 mg/kg on days 2-5 1
• Has demonstrated efficacy and safety in pediatric CAP, including atypical pneumonia caused by M. pneumoniae and C. pneumoniae 4

Skin and Soft Tissue Infections

• Specific pediatric dosing for SSTIs not explicitly stated in guidelines, but would follow general pediatric dosing principles 5

Special Considerations

Renal Impairment

• Mild to moderate impairment (GFR 10-80 mL/min): No dosage adjustment required 1
• Severe impairment (GFR <10 mL/min): Use with caution as AUC increases by 35% 1

Hepatic Impairment

• No specific dose adjustments recommended due to limited pharmacokinetic data 1
• Use with caution in patients with significant hepatic disease

Duration of Therapy

• Community-acquired pneumonia:
  • Standard bacterial pathogens: 7-10 days 5
  • Atypical pathogens (M. pneumoniae, C. pneumoniae): 10-14 days 5, 6
  • Azithromycin specifically: 5 days (due to prolonged tissue half-life) 6
• Skin and soft tissue infections: ~7 days, depending on clinical response 5

Treatment Algorithm

1. Assess infection type and severity:

   • Mild-moderate CAP or uncomplicated SSTI → Oral azithromycin monotherapy
   • Severe CAP or complicated SSTI → Consider combination therapy

2. Evaluate patient factors:

   • Renal function: Use caution if GFR <10 mL/min
   • Risk for QT prolongation: Avoid in patients with known QT prolongation, history of torsades de pointes, or concurrent use of other QT-prolonging medications 6
   • Recent antibiotic exposure: Consider alternative class if recent macrolide use

3. Monitor treatment response:

   • Clinical improvement expected within 48-72 hours
   • If no improvement after 72 hours, reassess diagnosis and consider alternative therapy

Clinical Pearls and Caveats

• Azithromycin remains in tissues longer than most antibiotics due to its 11-14 hour half-life, allowing for shorter treatment courses 5
• For hospitalized non-ICU patients with CAP, guidelines recommend either a respiratory fluoroquinolone OR a β-lactam plus a macrolide (such as azithromycin) 5
• In areas with high macrolide resistance, azithromycin monotherapy may not be appropriate for empiric treatment of CAP 6
• Azithromycin can be taken with or without food 1

By following these dosing guidelines and considering patient-specific factors, azithromycin can be effectively used to treat various bacterial infections while minimizing the risk of adverse effects and treatment failure.