Which antibiotic is commonly used to treat pertussis in infants older than 1 month?

Which antibiotic is commonly used to treat pertussis in infants older than 1 month?

• A. Azithromycin
• B. Erythromycin
• C. Amoxicillin
• D. Cephalexin

Answer: (B)

Macrolide antibiotics are the treatment choice for pertussis because they inhibit protein synthesis in Bordetella pertussis and help clear the infection, which also reduces contagiousness when started early.

Erythromycin is a classic macrolide that has long been used in infants older than one month to treat pertussis, with established dosing guidelines and proven effectiveness against B. pertussis. This makes it the best match among the options for this scenario. Amoxicillin and cephalexin target other bacteria and do not reliably treat pertussis, so they aren’t appropriate choices here. Azithromycin is another macrolide and is effective, but the question aligns with erythromycin as the commonly used option in this age group.