What is the treatment for pertussis (whooping cough) in a 3-month-old infant?

Treatment of Pertussis in a 3-Month-Old Infant

Azithromycin is the preferred first-line treatment for pertussis in a 3-month-old infant, administered at a dose of 10 mg/kg per day for 5 days. 1

First-Line Treatment

Azithromycin Regimen

• Dosage for infants <6 months: 10 mg/kg per day for 5 days 2, 1
• Administration: Once daily oral dosing
• Advantages:
  • Better tolerated than other macrolides 3
  • Lower risk of infantile hypertrophic pyloric stenosis (IHPS) compared to erythromycin 2
  • Higher compliance rates due to once-daily dosing and shorter treatment course 3

Rationale for Azithromycin Selection

Azithromycin is strongly preferred for infants <1 month due to the risk of IHPS with erythromycin 1. Although the patient is 3 months old, azithromycin remains the preferred agent due to:

1. Excellent bacterial eradication rates (100% in clinical studies) 3
2. Significantly fewer gastrointestinal adverse events compared to erythromycin (18.8% vs 41.2%) 3
3. Better compliance with the shorter treatment course 3
4. Convenient once-daily dosing schedule 2

Alternative Treatment Options

If azithromycin cannot be used (e.g., hypersensitivity), consider:

Clarithromycin

• Dosage: 15 mg/kg/day divided into two doses for 7 days 1
• Note: Limited data in infants <6 months but appears effective 2

Trimethoprim-Sulfamethoxazole (TMP-SMX)

• Only if macrolides cannot be used
• Dosage: 8 mg/kg/day TMP, 40 mg/kg/day SMX in 2 divided doses for 14 days 1
• Not recommended for infants <2 months due to risk of kernicterus

Erythromycin (Not Preferred)

• Not recommended for infants <1 month due to risk of IHPS 2, 4
• Higher risk of gastrointestinal side effects 3
• Less convenient dosing (multiple daily doses for 14 days) 2

Monitoring and Supportive Care

• Monitor for signs of IHPS (projectile vomiting, irritability with feeding) even with azithromycin 2, 4
• Observe for respiratory distress, apnea, or cyanosis which may require hospitalization
• Ensure adequate hydration and nutrition
• Consider hospitalization for infants with severe symptoms or complications
• Monitor oxygen saturation in severe cases

Disease Course and Complications

Pertussis in infants <4 months carries significant risk for severe complications including:

• Apnea
• Pneumonia
• Seizures
• Death 5

Additional Considerations

• Household contacts should receive antibiotic prophylaxis with the same regimens as treatment 2, 1
• Isolate the patient for 5 days after starting antibiotic therapy 1
• Ensure the infant's vaccination status is up to date according to the recommended schedule
• Educate caregivers that antibiotics may not reduce the duration or severity of cough if started after the catarrhal stage 5

Follow-up

• Clinical reassessment within 48-72 hours to ensure improvement
• Monitor for potential complications, especially respiratory distress
• Ensure completion of the full antibiotic course

Pertussis in a 3-month-old requires prompt treatment with azithromycin to reduce transmission risk and prevent complications, even though antibiotics may have limited effect on symptom duration if started after the catarrhal stage.