When is azithromycin (Zithromax) used?

When is Azithromycin Used?

Azithromycin is used for respiratory infections (including community-acquired pneumonia, acute bacterial sinusitis, and acute exacerbations of COPD), sexually transmitted infections (particularly chlamydia), certain skin infections, and as long-term therapy in specific chronic respiratory conditions. 1

Approved Indications (FDA)

Azithromycin is FDA-approved for the following conditions 1:

Adults:

• Acute bacterial exacerbations of COPD (caused by H. influenzae, M. catarrhalis, or S. pneumoniae)
• Acute bacterial sinusitis (caused by H. influenzae, M. catarrhalis, or S. pneumoniae)
• Community-acquired pneumonia (caused by C. pneumoniae, H. influenzae, M. pneumoniae, or S. pneumoniae) in patients appropriate for oral therapy
• Pharyngitis/tonsillitis (as alternative to first-line therapy)
• Uncomplicated skin and skin structure infections
• Urethritis and cervicitis due to C. trachomatis or N. gonorrhoeae
• Genital ulcer disease in men due to H. ducreyi (chancroid)

Pediatric Patients:

• Acute otitis media
• Community-acquired pneumonia
• Pharyngitis/tonsillitis (as alternative to first-line therapy)

Off-Label Uses with Strong Evidence

Sexually Transmitted Infections

• Chlamydia infection: Azithromycin 1g as a single dose is recommended as an alternative to doxycycline (which is the preferred first-line treatment) 2
• The efficacy of azithromycin for urogenital chlamydia is approximately 92%, compared to 95.5% for doxycycline 2
• For rectal chlamydia infections, azithromycin has significantly lower efficacy (76.4%) compared to doxycycline (96.9%) 2

Chronic Respiratory Conditions

• Cystic Fibrosis: For patients ≥6 years with Pseudomonas aeruginosa persistently present in airways, azithromycin is recommended as chronic therapy to improve lung function and reduce exacerbations 3
• Bronchiectasis: Azithromycin is recommended as long-term therapy in patients with ≥3 exacerbations in the previous 12 months 3
• COPD: May be used in patients with frequent exacerbations despite optimal inhaled therapy 3

Dosing Considerations

Standard Treatment Courses:

• Respiratory infections: Typically 500mg on day 1, followed by 250mg daily for 4 days (5-day course) 4, 5
• Chlamydia: 1g as a single dose 2
• Chronic therapy for bronchiectasis/CF: Usually 250-500mg three times weekly 3

Special Populations:

• Pregnancy: Azithromycin is pregnancy category B and may be used when benefits outweigh risks 3, 2
• Children: Dosing is weight-based; azithromycin is approved for children ≥6 months 1, 4

Important Precautions and Monitoring

Antimicrobial Resistance Concerns

• Long-term azithromycin use can select for macrolide-resistant bacteria 3
• The long half-life (68 hours) creates a prolonged period of subinhibitory concentrations, potentially promoting resistance 3
• Prior to initiating long-term therapy, patients should be screened for nontuberculous mycobacterial (NTM) infection, as macrolide-resistant NTM disease has poor treatment outcomes 3

Cardiac Considerations

• QT prolongation risk - obtain family history of arrhythmias before initiating 3
• ECG may be warranted in patients with cardiac risk factors 3

Algorithm for Appropriate Use

1. For acute bacterial infections:

   • Confirm appropriate indication (respiratory, STI, skin)
   • Ensure patient is appropriate for oral therapy
   • For pneumonia: Avoid in severe illness requiring hospitalization 1
   • For STIs: Consider as alternative when doxycycline cannot be used or adherence is a concern 2

2. For chronic/prophylactic use:

   • Confirm diagnosis (CF, bronchiectasis, COPD)
   • Verify exacerbation frequency (typically ≥3 per year)
   • Screen for NTM infection before starting 3
   • Monitor for adverse effects and development of resistance
   • Ensure adherence is ≥70% for efficacy and to reduce resistance risk 3

Azithromycin's unique pharmacokinetic properties (high tissue concentrations, long half-life) make it particularly useful for short-course therapy of acute infections and intermittent dosing for chronic conditions, improving adherence compared to medications requiring more frequent administration 6.