Azithromycin 250mg Z-Pak Standard Dosing Regimen
The standard Z-pak regimen is 500 mg on day 1, followed by 250 mg once daily on days 2 through 5, for a total 5-day course. 1, 2, 3
Standard Adult Dosing
- Take 500 mg (two 250 mg tablets) on the first day, then 250 mg (one tablet) once daily for days 2,3,4, and 5 for respiratory tract infections including community-acquired pneumonia, acute bacterial sinusitis, and bronchitis 1, 2
- This provides a total dose of 1.5 grams over 5 days 1
- The FDA label confirms this is the standard regimen, with bioequivalence between two 250 mg tablets and a single 500 mg tablet 3
Alternative Regimens for Specific Indications
- For respiratory tract infections, a 3-day regimen of 500 mg once daily for 3 consecutive days is equally effective and provides the same total 1.5 gram dose 2, 4
- For non-gonococcal urethritis or chlamydial infections, use a single 1 gram dose instead of the Z-pak 1, 2
- For streptococcal pharyngitis/tonsillitis in penicillin-allergic patients, use 12 mg/kg once daily (maximum 500 mg) for 5 days due to higher recurrence rates with standard dosing 5, 6
Critical Administration Considerations
- Separate azithromycin from aluminum- or magnesium-containing antacids by at least 2 hours, as antacids reduce absorption by up to 50% 1, 2, 3
- Food increases Cmax by 23-56% but does not affect overall absorption (AUC), so the medication can be taken with or without food 3
- Dispense medication on-site and directly observe the first dose when possible to maximize adherence 1, 2
Pharmacokinetic Rationale
- Azithromycin achieves tissue concentrations 10-100 times higher than serum concentrations, with a terminal elimination half-life of 68 hours 3, 7
- Following the 5-day regimen, therapeutic concentrations persist in respiratory tissues for up to 10 days after the last dose 8, 7
- This prolonged tissue retention allows for shorter treatment courses compared to other antibiotics 4, 7
Important Clinical Caveats
- Azithromycin is NOT first-line for streptococcal pharyngitis due to increasing macrolide resistance; use only in penicillin-allergic patients 2, 5
- Never use as monotherapy for gonococcal infections due to widespread resistance; must combine with ceftriaxone if gonorrhea is suspected 1
- Obtain baseline ECG in patients with cardiac risk factors, and avoid if QTc >450 ms (men) or >470 ms (women) 1, 2
- Common gastrointestinal side effects (nausea, diarrhea, abdominal pain) are generally mild to moderate and less frequent than with erythromycin 1, 3, 4