How to manage a 5-month-old infant with continuous coughing, post-tussive vomiting, and suspected pertussis, already on Day 1 of Azithromycin (Azithromycin)?

Management of 5-Month-Old with Suspected Pertussis on Day 1 of Azithromycin

Continue the azithromycin at 10 mg/kg/day for the full 5-day course, as this is the CDC-recommended first-line treatment for infants under 6 months with pertussis, and focus on supportive care since antibiotics will not alter the clinical course of established paroxysmal coughing. 1

Antibiotic Management

• The current azithromycin regimen is correct: 10 mg/kg per day for 5 days is the CDC-recommended dosing for infants aged 1-5 months 1
• Do not expect clinical improvement from the antibiotic: Antibiotics eliminate B. pertussis from the nasopharynx (rendering the infant non-infectious) but do not alter the subsequent clinical course of paroxysmal coughing, post-tussive vomiting, or apnea once the paroxysmal phase has begun 2, 3, 4
• Complete the full 5-day course to achieve 100% bacterial eradication and prevent transmission 4
• Monitor for infantile hypertrophic pyloric stenosis (IHPS): While azithromycin has a significantly lower risk than erythromycin, infants under 6 months receiving macrolides should be monitored for IHPS (watch for projectile vomiting, visible peristaltic waves, palpable olive-shaped mass) 1

Supportive Care for Coughing and Post-Tussive Vomiting

Immediate Comfort Measures

• Position the infant upright or semi-upright during and after coughing episodes to reduce aspiration risk and facilitate mucus clearance
• Offer small, frequent feedings rather than large volume feeds to minimize post-tussive vomiting 1
• Feed shortly after a coughing episode when the infant may have a brief refractory period before the next paroxysm
• Maintain adequate hydration: Monitor for signs of dehydration from vomiting (decreased urine output, dry mucous membranes, sunken fontanelle)

Environmental Modifications

• Minimize stimuli that trigger coughing: Keep the environment calm, avoid sudden temperature changes, reduce exposure to irritants (smoke, strong odors)
• Use a cool-mist humidifier to help keep airways moist, though evidence for benefit is limited
• Ensure close observation: Never leave the infant unattended during coughing episodes due to risk of apnea, cyanosis, or aspiration

Critical Safety Monitoring

Indications for Hospitalization (Low Threshold for 5-Month-Old)

• Apneic episodes (breathing pauses >10-15 seconds)
• Cyanosis during or after coughing paroxysms
• Severe post-tussive vomiting leading to dehydration or inability to maintain oral intake
• Respiratory distress (grunting, nasal flaring, retractions, tachypnea)
• Oxygen desaturation below 90-92%
• Any concerning change in mental status or lethargy 1, 2

Infants under 6 months, especially under 4 months, have the highest risk of severe and fatal pertussis complications, so maintain a very low threshold for hospital admission 1

What NOT to Do

• Do not use cough suppressants (dextromethorphan, codeine): These have no proven benefit in controlling pertussis paroxysms and may be harmful in infants 2
• Do not use corticosteroids, long-acting β-agonists, antihistamines, or pertussis immunoglobulin: None of these therapies have demonstrated benefit in controlling coughing paroxysms 2
• Do not give azithromycin with aluminum- or magnesium-containing antacids simultaneously, as they reduce absorption 1

Expected Clinical Course

• Paroxysmal coughing will persist for weeks to months despite appropriate antibiotic therapy, as the disease typically lasts 6-10 weeks total (the "100-day cough") 2, 3
• The infant becomes non-infectious after 5 days of azithromycin but symptoms will continue 2, 4
• Approximately 80-90% of untreated patients spontaneously clear B. pertussis within 3-4 weeks, but treatment is still indicated to prevent transmission 2

Household Contact Management

• All household contacts should receive prophylaxis with the same antibiotic regimen (azithromycin dosing per age), especially critical given the presence of a vulnerable infant 1, 2
• Symptomatic household members should be treated as if they have pertussis 1

Common Pitfall to Avoid

The most critical pitfall is expecting antibiotics to stop the coughing and vomiting—they will not. Parents must understand that azithromycin prevents spread but does not provide symptomatic relief, and the paroxysmal phase may last many weeks regardless of treatment. 2, 3, 4 This expectation management is essential to prevent premature discontinuation of antibiotics or unnecessary additional interventions.