What is the recommended dosage and regimen for azithromycin (Z pack) in an adult patient with normal kidney function and no known allergies to antibiotics?

How to Write an Order for Azithromycin (Z-Pack)

Standard Adult Z-Pack Order

For an adult patient with normal kidney function and no antibiotic allergies, write: "Azithromycin 500 mg PO on day 1, then 250 mg PO once daily on days 2-5" for respiratory tract infections. 1, 2, 3

Alternative Dosing Regimens by Indication

Respiratory Tract Infections

• 5-day regimen (standard Z-pack): 500 mg on day 1, followed by 250 mg once daily on days 2-5 1, 2, 3
• 3-day regimen (equally effective): 500 mg once daily for 3 consecutive days, providing the same total 1.5 gram dose with improved compliance 1, 2, 3
• Both regimens deliver equivalent tissue concentrations and clinical outcomes for community-acquired pneumonia, acute bacterial sinusitis, and bronchitis 1, 2

Sexually Transmitted Infections

• Chlamydia trachomatis (non-gonococcal urethritis/cervicitis): Single 1 gram dose PO 1, 4, 2
• This single-dose regimen provides therapeutic tissue concentrations in urogenital tissues for approximately 10 days due to azithromycin's prolonged tissue half-life 1, 5
• Critical: Never use azithromycin as monotherapy for gonorrhea due to resistance; must combine with ceftriaxone 500 mg IM 1, 2

Mycoplasma genitalium

• Extended regimen: 500 mg on day 1, then 250 mg daily for 4 additional days 4
• Use this extended regimen rather than single-dose for persistent non-gonococcal urethritis 4

Order Writing Format

Write the prescription as:

• "Azithromycin 250 mg tablets"
• "Dispense: 6 tablets" (for standard 5-day regimen) 2
• "Sig: Take 2 tablets (500 mg) by mouth on day 1, then take 1 tablet (250 mg) by mouth once daily on days 2 through 5" 1, 2

Alternatively, for the 3-day regimen:

• "Azithromycin 500 mg tablets"
• "Dispense: 3 tablets" 1
• "Sig: Take 1 tablet (500 mg) by mouth once daily for 3 days" 1, 2

Critical Administration Instructions

Timing and Food

• Azithromycin can be taken with or without food, though food increases Cmax by 23% for tablets without affecting overall absorption 3
• Separate from antacids by at least 2 hours: Aluminum- or magnesium-containing antacids reduce absorption by up to 50% 1, 2

Dispensing Strategy

• Dispense medication on-site when possible and directly observe the first dose to maximize adherence, particularly for sexually transmitted infection treatment 1, 2
• This is especially important in populations with erratic healthcare-seeking behavior 1

Safety Precautions and Contraindications

Cardiac Screening

• Obtain baseline ECG in patients with cardiac risk factors before initiating therapy 1, 2
• Contraindicated if QTc >450 ms (men) or >470 ms (women) due to risk of QT prolongation and cardiac arrhythmias 1, 2
• Azithromycin increased cardiovascular deaths (HR 2.88; 95% CI 1.79-4.63) in a Tennessee Medicaid cohort, most pronounced in patients with high baseline cardiovascular risk 1

Hepatic Considerations

• Use with caution and increase monitoring if underlying liver disease is present 1
• Measure baseline liver function tests for long-term therapy 1

Renal Dosing

• No adjustment needed for mild to moderate renal impairment (GFR 10-80 mL/min), as Cmax and AUC increase by only 5.1% and 4.2% respectively 3
• Exercise caution in severe renal impairment (GFR <10 mL/min), where Cmax increases 61% and AUC increases 35% 1, 3

Common Pitfalls to Avoid

Inappropriate Indications

• Do NOT use azithromycin as first-line for streptococcal pharyngitis due to increasing macrolide resistance in group A Streptococcus; reserve as alternative only in penicillin-allergic patients 2
• Do NOT use the 1 gram single dose for streptococcal pharyngitis—this indication requires the standard 5-day regimen or higher-dose regimens (12 mg/kg/day for 5 days in children) 4
• Do NOT use as monotherapy for gonococcal infections due to resistance 1, 2

Drug Interactions

• Avoid in patients taking other QT-prolonging medications without careful risk assessment 1
• Nelfinavir significantly increases azithromycin Cmax and AUC, though no dose adjustment is recommended 3

Patient Counseling

• For sexually transmitted infections, patients should abstain from sexual intercourse for 7 days after completing therapy to prevent transmission 1
• Common side effects include gastrointestinal symptoms (nausea, vomiting, abdominal pain, diarrhea), which are generally mild to moderate and less frequent than with erythromycin 1, 2

Special Populations

Pregnancy

• Azithromycin is FDA Pregnancy Category B and considered safe in pregnancy 1, 2
• Single 1 gram dose is an alternative regimen for chlamydial infections in pregnancy 1

Pediatric Dosing

• Standard regimen: 10 mg/kg (maximum 500 mg) on day 1, followed by 5 mg/kg once daily (maximum 250 mg/day) on days 2-5 1, 2, 6
• Alternative 3-day regimen: 10 mg/kg/day (maximum 500 mg) for 3 days 6, 5