What is the recommended dose of azithromycin (Zithromax) for treating pertussis in children?

Azithromycin Dosing for Pertussis in Children

For children ≥6 months, administer azithromycin 10 mg/kg (maximum 500 mg) on day 1, followed by 5 mg/kg per day (maximum 250 mg) on days 2-5; for infants <6 months, give 10 mg/kg per day for 5 consecutive days. 1, 2

Age-Specific Dosing Regimens

Infants <6 Months

• Administer 10 mg/kg per day for 5 days 1, 2
• This simplified regimen uses the same daily dose throughout the treatment course, making it easier for caregivers to administer 1
• Azithromycin is the preferred macrolide for infants <1 month due to significantly lower risk of infantile hypertrophic pyloric stenosis (IHPS) compared to erythromycin 2, 3

Children ≥6 Months

• Day 1: 10 mg/kg (maximum 500 mg) 1, 2
• Days 2-5: 5 mg/kg per day (maximum 250 mg) 1, 2
• This weight-based dosing regimen has been validated in multiple clinical trials demonstrating 100% bacterial eradication rates 4

Clinical Effectiveness and Timing

Start antibiotics immediately upon clinical suspicion without waiting for culture confirmation, as early treatment during the catarrhal phase (first 2 weeks) rapidly clears B. pertussis from the nasopharynx and decreases coughing paroxysms 2. Treatment initiated during the paroxysmal phase (>3 weeks) has limited clinical benefit for symptom control but remains indicated to prevent transmission 2.

Key Evidence Points:

• Azithromycin achieves 100% bacterial eradication at end of therapy in culture-confirmed pertussis 4
• No bacterial recurrence occurs after completing the azithromycin regimen 4
• The 5-day azithromycin course is equally effective as the traditional 14-day erythromycin regimen 4, 5

Safety and Tolerability Advantages

Azithromycin causes significantly fewer gastrointestinal adverse events compared to erythromycin (18.8% vs 41.2%), with less nausea (2.9% vs 8.4%), vomiting (5.0% vs 13.0%), and diarrhea (7.1% vs 11.8%) 4. This superior tolerability translates to markedly better compliance: 90% of children complete 100% of azithromycin doses versus only 55% with erythromycin 4.

Important Administration Considerations

Drug Interactions and Contraindications:

• Do not administer azithromycin simultaneously with aluminum- or magnesium-containing antacids, as they reduce absorption 1, 2
• Use with caution in patients with impaired hepatic function 1, 2
• Monitor for drug interactions when used with agents metabolized by cytochrome P450 (e.g., digoxin, triazolam, ergot alkaloids) 1, 2
• Contraindicated in patients with history of hypersensitivity to any macrolide 1, 2

Special Monitoring for Young Infants:

• Infants <1 month receiving macrolides should be monitored for IHPS and other serious adverse events 1
• Despite this risk, the benefits of treating pertussis in this age group outweigh potential complications, as severe pertussis can be life-threatening 1

Postexposure Prophylaxis

Use the same dosing regimens for postexposure prophylaxis as for treatment 1, 2. Prophylaxis is particularly critical in exposure settings that include infants <12 months or women in the third trimester of pregnancy, as severe and sometimes fatal complications occur most frequently in young infants 1, 2.

Isolation Requirements

Isolate patients at home and away from work/school for 5 days after starting antibiotics to prevent transmission 2. Approximately 80-90% of untreated patients spontaneously clear B. pertussis within 3-4 weeks from cough onset, but antibiotic treatment significantly shortens this communicable period 2.