What is the appropriate dosage of azithromycin (Z pack) for a 12-year-old?

Azithromycin Dosing for a 12-Year-Old

For a 12-year-old child, azithromycin should be dosed at 10 mg/kg (maximum 500 mg) on day 1, followed by 5 mg/kg (maximum 250 mg) once daily on days 2-5 for a standard 5-day course. 1

Standard Weight-Based Calculation

• A typical 12-year-old weighing approximately 40 kg would receive 400 mg on day 1, then 200 mg daily for days 2-5 1
• The maximum daily dose is capped at 500 mg on day 1 and 250 mg on subsequent days, regardless of weight 2, 1
• This dosing regimen applies to most common pediatric infections including community-acquired pneumonia (atypical pathogens), acute otitis media, and pertussis 2, 1

Indication-Specific Considerations

For Atypical Pneumonia (Mycoplasma or Chlamydia)

• The preferred oral regimen remains 10 mg/kg day 1, then 5 mg/kg days 2-5 2, 3
• Clinical improvement should be evident within 48-72 hours; if fever persists beyond 72 hours or respiratory symptoms worsen, consider alternative diagnoses 3
• If hospitalization is required, use IV azithromycin 10 mg/kg on days 1-2, then transition to oral therapy as soon as feasible 2, 3

For Streptococcal Pharyngitis

• A higher total dose of 60 mg/kg is required for adequate GABHS eradication, given as either 12 mg/kg once daily for 5 days or 20 mg/kg once daily for 3 days 4
• This higher dosing is necessary because standard azithromycin regimens result in more recurrences compared to penicillin V for strep throat 5, 4

For Pertussis Treatment or Prophylaxis

• Use the standard 5-day regimen: 10 mg/kg (max 500 mg) day 1, then 5 mg/kg (max 250 mg) days 2-5 2

Alternative Regimens

• A 3-day course of 10 mg/kg daily is recognized as effective for some respiratory infections, though the 5-day regimen is generally preferred 3, 6
• A single 30 mg/kg dose has been studied for acute otitis media but is associated with more gastrointestinal adverse effects 7, 8

Critical Clinical Pitfalls to Avoid

Wrong Indication

• Azithromycin is NOT first-line for typical bacterial pneumonia caused by S. pneumoniae or H. influenzae—beta-lactam antibiotics (amoxicillin, amoxicillin-clavulanate) remain first-line for these typical pathogens 1
• Do not combine azithromycin with beta-lactams for mycoplasma coverage, as mycoplasma lacks a cell wall and is inherently resistant to all beta-lactam antibiotics 3

Drug Interactions

• Do not administer azithromycin simultaneously with aluminum- or magnesium-containing antacids, as they reduce absorption 2, 1
• Monitor for QT prolongation when used with other QT-prolonging medications 1

Duration Errors

• The standard 5-day course is sufficient for uncomplicated infections; extended courses beyond 5 days are not routinely recommended unless there is documented treatment failure or severe disease 3
• For hospitalized patients, limit IV azithromycin to days 1-2 only, then transition to oral therapy when feasible 1, 3

Safety Profile

• Azithromycin has fewer gastrointestinal side effects than erythromycin, with treatment-related adverse events occurring in approximately 9% of pediatric patients 2, 5, 9
• The most common side effects are mild to moderate gastrointestinal complaints (diarrhea, abdominal pain, nausea), occurring in 5-6% of children 2, 9
• Treatment discontinuation due to adverse events is rare (1.3% of patients) 9

Practical Administration

• Azithromycin suspension is well-tolerated by children, who find the color and taste agreeable 8
• The once-daily dosing significantly improves compliance compared to multiple-daily-dose regimens 5, 4
• For a 12-year-old who can swallow pills, tablets may be used instead of suspension 1