Can a 13-year-old male weighing 117 lb (≈53 kg) be prescribed a Z‑Pak (azithromycin)?

Can a 13-Year-Old Male Weighing 117 lb Be Prescribed Azithromycin (Z-Pak)?

Yes, azithromycin can be safely prescribed to a 13-year-old male weighing 117 lb (53 kg), provided there is an appropriate indication and no contraindications. 1, 2

Weight-Based Dosing for This Patient

At 53 kg, this adolescent falls into the ≥46 kg weight band, which corresponds to adult dosing for azithromycin. 1

Standard Dosing Regimens by Indication

For respiratory tract infections (community-acquired pneumonia, atypical pneumonia):

• Day 1: 500 mg once daily
• Days 2–5: 250 mg once daily
• Total duration: 5 days 1, 2, 3

For uncomplicated chlamydial urethritis/cervicitis (if applicable in adolescents):

• Single dose: 1 gram orally 4, 2

For streptococcal pharyngitis (second-line only):

• 12 mg/kg once daily for 5 days (maximum 500 mg/day), because standard dosing has higher recurrence rates for strep throat 1, 3

Key Clinical Context: When to Use Azithromycin

Appropriate Indications

• Atypical respiratory pathogens: Mycoplasma pneumoniae, Chlamydia pneumoniae, Chlamydia trachomatis 1, 2, 3
• Community-acquired pneumonia when atypical organisms are suspected 1, 2
• Documented penicillin allergy in patients requiring treatment for susceptible organisms 1, 2
• Pertussis treatment or prophylaxis (10 mg/kg day 1, then 5 mg/kg days 2–5) 1

When NOT to Use Azithromycin

• Typical bacterial pneumonia caused by Streptococcus pneumoniae or Haemophilus influenzae—amoxicillin 90 mg/kg/day remains first-line 1
• Streptococcal pharyngitis—penicillin or amoxicillin are first-line; azithromycin is second-line only 1, 3
• Patients with prolonged QTc (>450 ms in males, >470 ms in females) or those taking other QT-prolonging medications 1, 4
• History of cholestatic jaundice or hepatic dysfunction associated with prior azithromycin use 5

Administration and Safety Considerations

How to Give Azithromycin

• Can be taken with or without food 1
• Do NOT administer simultaneously with aluminum- or magnesium-containing antacids—separate by at least 2 hours to avoid reduced absorption 1, 4
• Oral suspension is available for patients who cannot swallow tablets 1

Expected Clinical Response

• Patients should show clinical improvement within 48–72 hours of starting therapy 1
• If no improvement or deterioration occurs, reassess for:
  • Incorrect diagnosis or resistant pathogens 1
  • Complications such as parapneumonic effusion 1
  • Need for alternative or additional antimicrobial therapy 1

Common Pitfalls to Avoid

• Do not underdose the initial 500 mg dose on day 1—full dosing is essential to achieve therapeutic tissue levels 1
• Do not prescribe azithromycin as first-line for typical bacterial pneumonia or strep throat—β-lactam agents have superior outcomes 1, 3
• Do not confuse azithromycin with other macrolides (e.g., clarithromycin requires twice-daily dosing at 7.5 mg/kg BID) 1
• Verify the specific infection type—azithromycin is most appropriate for atypical pathogens and should be used in areas with low pneumococcal macrolide resistance 4

Contraindications and Precautions

• Hypersensitivity to azithromycin, erythromycin, any macrolide, or ketolide 5
• History of cholestatic jaundice or hepatic dysfunction with prior azithromycin use 5
• Concurrent use with QT-prolonging medications (e.g., Class IA/III antiarrhythmics, certain antipsychotics) requires careful risk assessment 1, 4
• Patients with underlying hepatic disease should have liver function monitored 4

Adverse Effects

Common (mostly gastrointestinal):

• Abdominal discomfort, diarrhea, nausea, vomiting, headache, dizziness 5, 1, 4
• Better gastrointestinal tolerance than erythromycin 1, 3

Rare but serious:

• QT prolongation, torsades de pointes 5, 4
• Pseudomembranous colitis, acute interstitial nephritis, anaphylaxis 5, 1
• Stevens-Johnson syndrome, toxic epidermal necrolysis 5

FDA-Approved Pediatric Indications

The FDA label confirms azithromycin is approved for pediatric use in:

• Acute otitis media caused by H. influenzae, M. catarrhalis, or S. pneumoniae 2
• Community-acquired pneumonia due to C. pneumoniae, H. influenzae, M. pneumoniae, or S. pneumoniae in patients appropriate for oral therapy 2
• Pharyngitis/tonsillitis caused by S. pyogenes as an alternative to first-line therapy 2