Infectious Diseases and Immunization
Empiric choices by age and site
Organisms shift with age: group B Streptococcus, E. coli, and Listeria in neonates; Streptococcus pneumoniae and Neisseria meningitidis beyond the neonatal period. Acute otitis media: high-dose amoxicillin 80–90 mg/kg/day (to overcome intermediate-resistant pneumococcus), with amoxicillin-clavulanate for treatment failure or recent beta-lactam exposure. Streptococcal pharyngitis: penicillin V or amoxicillin 50 mg/kg once daily (max 1 g) for 10 days. Community-acquired pneumonia: amoxicillin, adding a macrolide at age 5 and older for atypical coverage. Bacterial meningitis beyond the neonatal period: vancomycin plus ceftriaxone (or cefotaxime); neonates add ampicillin. Serious MRSA disease: target vancomycin AUC/MIC 400–600. Avoid doxycycline under 8 years except selected rickettsial disease.
Immunization rules worth memorizing
Preterm infants are immunized by chronologic age, not corrected age. Two injectable live vaccines given on the same day are acceptable; if separated, space them at least 4 weeks. Live vaccines are contraindicated in severe immunodeficiency and pregnancy. Tdap is given each pregnancy at 27–36 weeks. Hepatitis B vaccine plus immune globulin within 12 hours of birth for infants of HBsAg-positive mothers. Egg allergy is no longer a barrier to influenza vaccine. Palivizumab is monthly RSV prophylaxis for high-risk infants.
Worked example
A 9 kg child with AOM and recent amoxicillin failure: amoxicillin-clavulanate 90 mg/kg/day of the amoxicillin component = 810 mg/day, divided twice daily (405 mg per dose), using the 600 mg/5 mL formulation to keep the clavulanate below 10 mg/kg/day and limit diarrhea.