What is the recommended treatment for a patient with pertussis, considering age, medical history, and potential allergies?

Treatment of Pertussis

Azithromycin is the first-line antibiotic for pertussis treatment across all age groups, with age-specific dosing: 10 mg/kg/day for 5 days in infants <6 months, 10 mg/kg (max 500 mg) on day 1 then 5 mg/kg/day (max 250 mg) on days 2-5 for children ≥6 months, and 500 mg on day 1 then 250 mg daily on days 2-5 for adults. 1

Immediate Treatment Initiation

• Start antibiotics immediately upon clinical suspicion without waiting for laboratory confirmation, as early treatment during the catarrhal phase (first 1-2 weeks) rapidly clears B. pertussis from the nasopharynx, decreases coughing paroxysms, and reduces complications by approximately 50%. 1, 2
• Even when started during the paroxysmal stage (>3 weeks), antibiotics remain critical for eradicating the organism and preventing transmission to vulnerable contacts, though clinical benefit to the patient is limited at this stage. 1, 2
• Approximately 80-90% of untreated patients will spontaneously clear B. pertussis within 3-4 weeks from cough onset. 1

Age-Specific Antibiotic Dosing

Infants <1 Month

• Azithromycin is the preferred agent due to significantly lower risk of infantile hypertrophic pyloric stenosis (IHPS) compared to erythromycin. 1
• Dosing: 10 mg/kg/day for 5 days. 1
• Avoid erythromycin in this age group due to strong association with IHPS. 1

Infants 1-5 Months

• Azithromycin 10 mg/kg/day for 5 days OR clarithromycin 7.5 mg/kg twice daily for 7 days. 1
• Both are first-line options based on in vitro effectiveness and safety. 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, 3
• Alternative: Clarithromycin 7.5 mg/kg (maximum 500 mg) twice daily for 7 days. 1, 4

Adults and Elderly

• Azithromycin: 500 mg on day 1, then 250 mg daily on days 2-5. 1, 2
• Alternative: Clarithromycin 500 mg twice daily for 7 days. 2

Alternative for Macrolide Contraindications

• Trimethoprim-sulfamethoxazole (TMP-SMZ) is the recommended alternative for patients >2 months with macrolide hypersensitivity or contraindications. 1
• Macrolides are contraindicated in patients with history of hypersensitivity to any macrolide agent. 1

Critical Medication Considerations

Drug Interactions and Administration

• Do not administer azithromycin simultaneously with aluminum- or magnesium-containing antacids as they reduce absorption. 1, 2
• Azithromycin does NOT inhibit cytochrome P450 enzymes, unlike erythromycin and clarithromycin. 1
• Obtain baseline ECG to exclude QTc prolongation before initiating azithromycin in patients taking citalopram or other QTc-prolonging medications. 1
• Use caution in patients with impaired hepatic function. 1, 2

Comparative Advantages of Azithromycin

• Equal efficacy to erythromycin for pertussis treatment. 1
• Superior tolerability with significantly fewer gastrointestinal side effects (4% vs 31% with erythromycin). 3
• Shorter treatment duration improves compliance. 2, 5
• Significantly lower IHPS risk in infants <6 months. 1

Infection Control Measures

• Isolate the patient at home and away from work/school for 5 days after starting antibiotics to prevent transmission. 1, 2
• Pertussis has a secondary attack rate exceeding 80% among susceptible household contacts. 1, 2

Postexposure Prophylaxis

• Administer the same antibiotic regimens and dosing used for treatment to all close contacts within 21 days of exposure, regardless of age or vaccination status. 1, 2
• Prophylaxis is especially critical if contacts include infants <12 months, pregnant women in the third trimester, or other vulnerable individuals. 1, 2
• All household contacts require macrolide prophylaxis to prevent transmission. 2

Therapies to Avoid

• Do not use β-agonists, antihistamines, corticosteroids, or pertussis immunoglobulin, as these have no proven benefit in controlling coughing paroxysms or improving clinical outcomes. 1, 2

Vaccination Considerations

• Verify and update vaccination status of the patient and all household contacts. 1
• Pregnant women should receive Tdap between 27-36 weeks' gestation with each pregnancy to convey immunity to the newborn. 1, 6
• Vaccine immunity wanes after 5-10 years, making previously vaccinated individuals susceptible to infection. 1

Common Pitfalls to Avoid

• Do not delay treatment waiting for laboratory confirmation—clinical suspicion alone warrants immediate antibiotic initiation. 2
• Do not assume treatment is futile in the paroxysmal stage—while clinical benefit may be limited, treatment remains essential to prevent transmission to vulnerable contacts. 2
• Do not use erythromycin in infants <6 months due to IHPS risk; azithromycin is preferred despite lack of FDA licensure in this age group. 1

Monitoring for Complications

• Watch for weight loss, sleep disturbance, and post-tussive vomiting, which occur frequently. 2, 4
• Monitor for pressure-related effects from severe coughing including pneumothorax, epistaxis, subconjunctival hemorrhage, and rib fractures. 2
• Infants <12 months, especially <4 months, have the highest risk of severe and fatal pertussis complications including apnea, pneumonia, seizures, and death. 1, 7