What is the standard dosing regimen for a Z (azithromycin) pack?

Z-Pack (Azithromycin) Standard Dosing

The standard Z-pack regimen is 500 mg on day 1, followed by 250 mg once daily on days 2 through 5, for a total course of 5 days. 1, 2, 3

Standard Adult Dosing Regimens

Five-Day Regimen (Most Common "Z-Pack")

• Day 1: 500 mg orally (typically two 250 mg tablets) 1, 3
• Days 2-5: 250 mg orally once daily 1, 3
• Total dose: 1.5 grams over 5 days 3

Three-Day Regimen (Alternative)

• 500 mg orally once daily for 3 consecutive days 3, 4
• Total dose: 1.5 grams over 3 days 3
• Both the 3-day and 5-day regimens provide comparable serum and tissue exposure when the same total dose is administered 3

Single-Dose Regimen (Specific Indications)

• 1 gram orally as a single dose for chlamydial infections (non-gonococcal urethritis/cervicitis) 1, 2
• This provides therapeutic tissue concentrations for approximately 10 days due to azithromycin's prolonged tissue half-life 5, 6

Pharmacokinetic Rationale

The unique dosing stems from azithromycin's exceptional tissue distribution and prolonged elimination:

• Tissue concentrations exceed plasma levels by 100-fold in lungs and tonsils, 70-fold in cervix, and 35-fold in skin 5
• Tissue half-life is approximately 68-72 hours, allowing once-daily dosing and short treatment courses 3, 7
• Therapeutic levels persist for 7-10 days after completing a 5-day course due to slow release from tissues 8, 6

Administration Considerations

Timing and Food

• Can be taken with or without food, though food increases Cmax by 23-56% without affecting overall absorption (AUC) 3
• Avoid concurrent antacids containing aluminum or magnesium, as they reduce absorption by up to 50%; separate by at least 2 hours 9, 3

First Dose Strategy

• Directly observed first dose is recommended to maximize compliance, particularly in populations with erratic healthcare-seeking behavior 1
• Dispense medication on-site when possible 1

Common Pitfalls and Caveats

Compliance Advantage

• Azithromycin's primary advantage over alternatives like doxycycline is the short duration and once-daily dosing, which significantly improves adherence 1, 2
• In populations where compliance is questionable, azithromycin should be preferred over 7-day regimens 1

Sexual Abstinence After Treatment

• Patients treated for sexually transmitted infections should abstain from sexual intercourse for 7 days after completing therapy to prevent transmission 1

Common Side Effects

• Gastrointestinal symptoms (nausea, vomiting, abdominal pain, diarrhea) are the most common adverse effects, though generally mild to moderate 5, 2
• These occur less frequently than with erythromycin 1, 8

Pregnancy Classification

• FDA Category B in pregnancy, making it safer than alternatives like doxycycline (contraindicated) or fluoroquinolones 5, 2

Pediatric Dosing (For Reference)

• Day 1: 10 mg/kg (maximum 500 mg) 2, 10
• Days 2-5: 5 mg/kg once daily (maximum 250 mg/day) 2, 10
• Alternative 3-day regimen: 10 mg/kg once daily for 3 days 10