Azithromycin Dosing for Adults
For most adult infections, azithromycin is dosed as 500 mg on day 1, followed by 250 mg once daily on days 2-5, for a total 5-day course. 1
Standard Adult Dosing Regimens
The FDA-approved dosing varies by indication 1:
Common Infections (5-Day Regimen)
- Community-acquired pneumonia (mild)
- Pharyngitis/tonsillitis (second-line)
- Skin/skin structure infections (uncomplicated)
Dose: 500 mg once daily on Day 1, then 250 mg once daily on Days 2-5
Alternative 3-Day Regimen
- Acute bacterial exacerbations of COPD
- Acute bacterial sinusitis
Dose: 500 mg once daily for 3 days
Single-Dose Regimens
- Non-gonococcal urethritis/cervicitis: 1 gram single dose
- Chancroid: 1 gram single dose
- Gonococcal urethritis/cervicitis: 2 grams single dose
Long-Term Prophylactic Dosing
For chronic respiratory conditions requiring long-term macrolide therapy 2, 3:
- Bronchiectasis/Asthma: 250-500 mg three times weekly, or 250 mg daily
- Starting dose: 250 mg three times weekly is pragmatic, can be increased based on clinical response 2
Hepatic Impairment Adjustment
No dose adjustment is required for moderate hepatic impairment (Child-Pugh Class A or B). 1, 4
The evidence is clear on this point:
- FDA labeling states: "No dose adjustment recommendations can be made in patients with impaired hepatic function" but notes that pharmacokinetic studies have not been performed 1
- However, a dedicated pharmacokinetic study in cirrhotic patients (Class A and B) showed no clinically significant differences in drug exposure (AUC), clearance, or volume of distribution compared to healthy volunteers 4
- Prescribe with caution in severe hepatic impairment, as azithromycin can cause hepatotoxicity 5, 6, 7, 8
Important Hepatic Considerations
While dose adjustment is not required, exercise caution and monitor liver function because:
- Azithromycin undergoes predominantly hepatic metabolism with biliary excretion 1
- Rare cases of drug-induced liver injury (DILI) have been reported, including cases with autoimmune features 8
- The 2020 NTM guidelines note "caution in severe hepatic impairment" for related macrolides 9
Baseline liver function tests should be measured before initiating therapy, checked at 1 month, then every 6 months during long-term use 3
Renal Impairment
No dose adjustment is required for renal impairment (GFR ≤80 mL/min), including severe impairment (GFR <10 mL/min), though caution is advised in severe cases 1. The mean AUC increased only 35% in patients with GFR <10 mL/min compared to normal renal function 1.
Administration
- Can be taken with or without food 1
- Food increases Cmax by 23-56% but does not affect overall absorption (AUC) 1
- Avoid concurrent aluminum/magnesium-containing antacids as they reduce absorption rate 5
Key Clinical Pearls
- The extensive tissue distribution (volume of distribution 31.1 L/kg) and prolonged terminal half-life of 68 hours allow for once-daily dosing and short treatment courses 1
- Tissue concentrations exceed serum levels by >100-fold in some tissues and remain above MIC for key pathogens for up to 10 days after a 5-day course 10
- Monitor for QTc prolongation: Obtain baseline ECG if using long-term therapy; contraindicated if QTc >450 ms (men) or >470 ms (women) 3