What is the recommended dosing for a Z-pack (azithromycin)?

Z-Pack Dosing for Azithromycin

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 5-day course. 1, 2, 3

Standard Adult Dosing Regimens by Indication

Respiratory Tract Infections

• For community-acquired pneumonia, acute bacterial sinusitis, and bronchitis: 500 mg on day 1, then 250 mg once daily on days 2-5 (total 5 days) 1, 2, 3
• Alternative 3-day regimen: 500 mg once daily for 3 consecutive days provides the same total 1.5 gram dose and is equally effective for respiratory infections 2, 3, 4
• For acute bacterial exacerbations of COPD: Either 500 mg daily for 3 days OR the standard 5-day regimen (500 mg day 1, then 250 mg days 2-5) 3

Sexually Transmitted Infections

• For non-gonococcal urethritis and cervicitis (Chlamydia): Single 1 gram dose orally 1, 2, 3
• For chancroid (genital ulcer disease): Single 1 gram dose 3
• Critical advantage: Single-dose regimens allow for directly observed therapy and dramatically improve compliance, particularly important in populations unlikely to return for follow-up 1

Pharyngitis/Tonsillitis

• Azithromycin is NOT first-line for streptococcal pharyngitis due to increasing macrolide resistance in Group A Streptococcus 2
• If used as second-line therapy (penicillin allergy): 500 mg day 1, then 250 mg days 2-5 3
• Important caveat: Azithromycin results in more recurrence of streptococcal infection than penicillin V, necessitating careful patient selection 5

Long-Term Prophylactic Regimens

• For bronchiectasis with ≥3 exacerbations per year: Azithromycin 500 mg three times weekly has the strongest evidence for reducing exacerbations 6, 1
• Alternative long-term dosing: 250 mg daily also has strong supportive evidence 6, 1
• Minimum duration: Therapy should continue for at least 6 months to demonstrate benefit in exacerbation reduction 6, 1
• For bronchiolitis obliterans syndrome in lung transplant recipients: 250 mg daily for 5 days, then 250 mg three times weekly for at least 3 months 6, 1

Pediatric Dosing

Respiratory Tract Infections

• Standard 5-day 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 2, 3, 5
• Alternative 3-day regimen: 10 mg/kg once daily for 3 consecutive days 3, 5
• For acute otitis media only: Single 30 mg/kg dose (maximum 1500 mg) is an option 3

Pharyngitis/Tonsillitis in Children

• Higher dose required: 12 mg/kg once daily for 5 days (maximum 500 mg/day) due to higher recurrence rates with standard dosing 7, 3, 5

Pertussis

• Infants <6 months: 10 mg/kg per day for 5 days 1, 2
• Children ≥6 months: 10 mg/kg (max 500 mg) on day 1, then 5 mg/kg (max 250 mg) on days 2-5 1, 2

Critical Administration Considerations

Food and Drug Interactions

• Azithromycin can be taken with or without food 2, 3
• Separate from antacids by at least 2 hours: Aluminum- or magnesium-containing antacids reduce absorption by up to 50% 1, 2, 8

Safety Monitoring for Long-Term Therapy

• Obtain baseline ECG to assess QTc interval before initiating long-term therapy 1, 2
• Contraindication: QTc >450 ms (men) or >470 ms (women) 1, 2
• Measure baseline liver function tests for long-term therapy 1
• Avoid in patients taking other QT-prolonging medications without careful risk assessment 1

Common Pitfalls and Clinical Pearls

Compliance Optimization

• Dispense medication on-site when possible and directly observe the first dose to maximize adherence 1, 2
• For STI treatment: Patients should abstain from sexual intercourse for 7 days after completing therapy 1

Resistance Concerns

• Never use azithromycin as monotherapy for gonorrhea due to widespread resistance; must combine with ceftriaxone if gonococcal infection suspected 1, 2
• Long-term macrolide use increases antimicrobial resistance, though clinical impact remains uncertain 6

Adverse Effects

• Common side effects: Diarrhea, abdominal pain, nausea, vomiting (less frequent than erythromycin) 6, 1, 5, 8
• Gastrointestinal symptoms are generally mild to moderate and better tolerated than amoxicillin/clavulanic acid in children 5

Special Populations

• Pregnancy: Classified as FDA Pregnancy Category B and considered safe 1, 2
• Infants <1 month: Azithromycin is preferred over erythromycin due to lower risk of infantile hypertrophic pyloric stenosis 1, 2
• Severe renal impairment (GFR <10 mL/min): Use with caution as AUC increases 35% compared to normal renal function 3
• Hepatic impairment: No dose adjustment recommendations available due to lack of pharmacokinetic data 3