Treatment of Pertussis
Azithromycin is the first-line antibiotic for treating pertussis across all age groups, with a 5-day regimen that is equally effective as erythromycin but better tolerated. 1
First-Line Antibiotic Treatment
Azithromycin Dosing by Age
Infants <1 month:
- Azithromycin is the preferred agent due to significantly lower risk of infantile hypertrophic pyloric stenosis (IHPS) compared to erythromycin 1
- Dose: 10 mg/kg/day for 5 days 1
- Note: Despite lack of FDA licensure in this age group, CDC explicitly recommends azithromycin because the risk of severe pertussis outweighs potential medication risks 1
Infants 1-5 months:
- Azithromycin or clarithromycin are first-line options 1
- Azithromycin dose: 10 mg/kg/day for 5 days 1
- Clarithromycin dose: 7.5 mg/kg twice daily for 7 days 1
Children ≥6 months and adolescents:
- Azithromycin: 10 mg/kg (maximum 500 mg) on day 1, then 5 mg/kg/day (maximum 250 mg) on days 2-5 1
Adults:
- Azithromycin: 500 mg on day 1, then 250 mg daily on days 2-5 1
Alternative Agents
Clarithromycin:
- Adults: 500 mg twice daily for 7 days 2
- Children: 7.5 mg/kg (maximum 500 mg) twice daily for 7 days 1, 3
- Equally effective as erythromycin with better tolerability 3
Trimethoprim-sulfamethoxazole (TMP-SMZ):
- Reserved for patients >2 months with macrolide contraindications or hypersensitivity 1
Erythromycin (avoid if possible):
- Should be avoided in infants <6 months due to strong association with IHPS 1
- If absolutely necessary: 40-50 mg/kg/day in children or 1-2 g/day in adults for 14 days 1, 4
- FDA-approved for pertussis and effective at eliminating organism from nasopharynx 4
Timing of Treatment and Expected Outcomes
Early treatment (catarrhal phase, first 1-2 weeks):
- Rapidly clears B. pertussis from nasopharynx 1
- Decreases coughing paroxysms and reduces complications 1
- Most effective period for clinical benefit 1
Late treatment (paroxysmal phase, >3 weeks):
- Limited clinical benefit for symptom improvement 1
- Still indicated to prevent transmission to others 1
- Natural history: 80-90% of untreated patients spontaneously clear bacteria within 3-4 weeks 1
Critical principle: Start antibiotics immediately upon clinical suspicion without waiting for culture confirmation 1
Isolation Requirements
- Isolate patient at home and away from work/school for 5 days after starting antibiotics 1
- Pertussis is highly contagious with secondary attack rate exceeding 80% among susceptible persons 1
Post-Exposure Prophylaxis (PEP)
Who should receive PEP:
- All household contacts (strongly recommended) 2
- Infants <12 months, especially <4 months 2
- Pregnant women in third trimester 2
- Healthcare workers with known exposure 1
PEP regimens:
- Use the same antibiotics and dosing as for treatment 1, 2
- Must be administered within 21 days of exposure to be effective 2
- Azithromycin is preferred agent 2
Important Drug Interactions and Precautions
Azithromycin:
- Do NOT take with aluminum- or magnesium-containing antacids (reduces absorption) 1
- Does NOT inhibit cytochrome P450 enzymes (unlike erythromycin and clarithromycin) 1
- Obtain baseline ECG in patients taking citalopram to exclude QTc prolongation before initiating 1
- Use with caution in patients with impaired hepatic function 1
Erythromycin and clarithromycin:
- Inhibit cytochrome P450 enzymes and can interact with digoxin, triazolam, ergot alkaloids 1
- Contraindicated in patients with macrolide hypersensitivity 1
Common Pitfalls to Avoid
- Do not delay treatment waiting for culture confirmation - start immediately on clinical suspicion 1
- Do not use erythromycin in infants <6 months - azithromycin is safer 1
- Do not prescribe β-agonists, antihistamines, corticosteroids, or pertussis immunoglobulin - these have no proven benefit for controlling coughing paroxysms 1
- Do not forget to treat household contacts - prophylaxis is critical to prevent transmission 2
- Remember that antibiotic resistance to erythromycin is rare (<1%) 1