Azithromycin (Z-pack) Dosing Regimen
The standard Z-pack (azithromycin) dosing regimen is 500 mg orally on day 1, followed by 250 mg once daily on days 2-5 for a total of 5 days.
Standard Dosing for Adults
- For most common infections requiring a Z-pack, the FDA-approved regimen is 500 mg (two 250 mg tablets) on day 1, followed by 250 mg once daily on days 2 through 5 1
- This 5-day regimen achieves therapeutic drug concentrations in tissues that persist for several days after the last dose due to azithromycin's long half-life (approximately 68-72 hours) 1, 2
- The extended tissue distribution and intracellular accumulation of azithromycin allow for this short-course therapy while maintaining efficacy 2
Alternative Dosing Regimens
- For chlamydial infections in adults and children ≥45 kg, a single 1 gram oral dose is recommended 3
- For children <45 kg with chlamydial infections, erythromycin base or ethylsuccinate 50 mg/kg/day orally divided into 4 doses daily for 14 days is recommended 3
- For treatment of certain MAC (Mycobacterium avium complex) infections, a daily regimen of clarithromycin (500-1000 mg) or azithromycin (250 mg) with ethambutol is recommended 3
Special Considerations
- For typhoid fever, a 7-day course of azithromycin 500 mg once daily is recommended 4
- For extended-release formulation (Zmax), a single 2.0 g dose is used for treatment of acute bacterial sinusitis or community-acquired pneumonia 5
- Food can increase the maximum concentration (Cmax) of azithromycin by 23-56%, but does not significantly affect the overall absorption (AUC) 1
- Antacids containing aluminum and magnesium hydroxide may reduce the peak concentration of azithromycin by 24% 1
Common Side Effects
- Gastrointestinal effects are most common: nausea, diarrhea, and abdominal pain 2, 6
- Azithromycin generally has better gastrointestinal tolerability compared to erythromycin 2, 7
Clinical Efficacy
- A 3-day regimen of azithromycin has been shown to be as effective as longer courses (5-10 days) of other antibiotics for respiratory tract infections 7, 8
- The convenient dosing schedule of azithromycin (once daily for 3-5 days) may improve patient compliance compared to more frequently administered antibiotics 6, 7
Important Cautions
- Pregnant women with chlamydial infections should not be treated with doxycycline, quinolones, or tetracyclines; erythromycin or amoxicillin is recommended instead 3
- For patients with severe cephalosporin allergy who have gonorrhea, consultation with infectious disease specialists is recommended as azithromycin resistance is emerging 3
- Azithromycin should be used with caution in patients with known QT interval prolongation or taking other medications that can prolong the QT interval 1
Remember that while the standard Z-pack is a 5-day regimen, specific conditions may require different dosing schedules, and treatment should be based on the specific infection being treated.