Azithromycin Dosing for Whooping Cough
For whooping cough, use azithromycin 10 mg/kg once daily for 5 consecutive days in infants under 6 months, and for older children/adults use 10 mg/kg (max 500 mg) on day 1 followed by 5 mg/kg (max 250 mg) on days 2-5. 1
Age-Based Dosing Regimens
Infants <6 Months
- 10 mg/kg once daily for 5 days 1
- This is the preferred regimen for neonates (<1 month) due to lower risk of infantile hypertrophic pyloric stenosis (IHPS) compared to erythromycin 1
- Azithromycin has not been associated with IHPS in infants <1 month, unlike erythromycin which carries significant risk 1
Infants and Children ≥6 Months
- Day 1: 10 mg/kg (maximum 500 mg)
- Days 2-5: 5 mg/kg once daily (maximum 250 mg per day) 1
- Total treatment duration: 5 days
Adolescents and Adults
- Day 1: 500 mg
- Days 2-5: 250 mg once daily 1
- Total treatment duration: 5 days
Key Clinical Considerations
Why Azithromycin Over Erythromycin
The CDC guidelines establish azithromycin as superior to the traditional 14-day erythromycin regimen because:
- Equally effective at eradicating Bordetella pertussis from the nasopharynx (100% eradication in both groups) 2
- Significantly fewer gastrointestinal side effects (18.8% vs 41.2% with erythromycin) 2
- Markedly better compliance (90% took all doses vs only 55% with erythromycin) 2
- Shorter treatment course (5 days vs 14 days) improves real-world adherence 3, 4
Critical Safety Point for Neonates
Azithromycin is the ONLY recommended macrolide for infants <1 month old 1. Erythromycin in this age group is associated with a dramatically increased risk of IHPS (7 cases out of 157 exposed infants vs 0 out of 125 unexposed; relative risk = infinity) 1. The high mortality risk from pertussis in neonates outweighs the theoretical risks of azithromycin, but these infants should still be monitored for IHPS and other adverse events 1.
Administration Details
Timing and Food
- Administer as a single daily dose 1
- Can be given with or without food 5
- Avoid concurrent aluminum- or magnesium-containing antacids as they reduce azithromycin absorption 1
Drug Interactions
Monitor patients taking:
- Drugs metabolized by cytochrome P450 system
- Digoxin, triazolam, or ergot alkaloids (pharmacokinetics may change) 1
- Azithromycin has fewer drug interactions than erythromycin or clarithromycin 1
Pregnancy and Lactation
- FDA Pregnancy Category B 1
- Same dosing as non-pregnant adults: 500 mg day 1, then 250 mg days 2-5
Common Pitfalls to Avoid
Don't underdose infants <6 months: They require 10 mg/kg daily for all 5 days, NOT the weight-tiered regimen used in older children 1
Don't use erythromycin in neonates unless azithromycin is absolutely unavailable, and if you must, monitor intensively for IHPS 1
Don't expect clinical improvement from antibiotics: While azithromycin effectively eradicates B. pertussis and prevents transmission, it does NOT alter the clinical course once paroxysmal cough has begun 3, 4. The benefit is preventing spread to others.
Don't delay treatment beyond 21 days: Antibiotics are most effective when started within 21 days of symptom onset in the index case 6. Effectiveness drops significantly after 14 days 6.
Postexposure Prophylaxis
For household contacts, use the same dosing regimens as for treatment 1. Prophylaxis is most effective when started within 14 days of the primary patient's symptom onset (43.9% effectiveness within 21 days, but declining after 14 days) 6.