What is the empirical antibiotic therapy for suspected meningitis in a 6-month-old?

Empirical Antibiotic Therapy for Suspected Meningitis in a 6-Month-Old

For a 6-month-old infant with suspected bacterial meningitis, immediately administer ceftriaxone 50 mg/kg IV every 12 hours (maximum 2g per dose) OR cefotaxime 75 mg/kg IV every 6-8 hours PLUS vancomycin 10-15 mg/kg IV every 6 hours (targeting serum trough concentrations of 15-20 μg/mL). 1

Rationale for This Regimen

The combination therapy provides comprehensive coverage for the most likely pathogens in this age group:

• Third-generation cephalosporin (ceftriaxone or cefotaxime) covers Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae 1
• Vancomycin is added to cover penicillin-resistant and cephalosporin-resistant S. pneumoniae strains 1

At 6 months of age, the infant falls into the "1 month to 18 years" category per ESCMID guidelines, which specifically recommends this dual-agent approach for empirical coverage 1. This age group has moved beyond the neonatal period where Listeria monocytogenes and gram-negative enteric organisms predominate, so ampicillin is not routinely required 1.

Dosing Specifics

Ceftriaxone option:

• 50 mg/kg IV every 12 hours (maximum 2g per dose) 1
• Infuse over 30 minutes 2

Cefotaxime option:

• 75 mg/kg IV every 6-8 hours 1
• Infuse over 30 minutes 1

Vancomycin (mandatory addition):

• 10-15 mg/kg IV every 6 hours 1
• Target serum trough concentrations of 15-20 μg/mL 1

Critical Timing Considerations

Antibiotics must be administered within 1 hour of hospital presentation. 1, 3 Delayed antibiotic administration is strongly associated with increased mortality and poor neurological outcomes 1, 3.

• Obtain blood cultures before antibiotics, but never delay treatment to wait for lumbar puncture or imaging 1, 3
• If lumbar puncture is delayed (e.g., for CT imaging), start empirical antibiotics immediately upon clinical suspicion 1, 3

Adjunctive Dexamethasone Therapy

Consider starting dexamethasone 0.15 mg/kg IV every 6 hours with or just before the first antibiotic dose 1. Dexamethasone has been shown to reduce mortality and neurological sequelae, particularly in pneumococcal meningitis 1. It can still be initiated up to 4 hours after the first antibiotic dose if not given initially 1.

Common Pitfalls to Avoid

• Do NOT use ceftriaxone alone without vancomycin in areas with any prevalence of penicillin-resistant pneumococci 1
• Do NOT delay antibiotics for imaging or lumbar puncture—the 1-hour window is critical 1, 3
• Do NOT use ceftriaxone with calcium-containing IV solutions in infants, as precipitation can occur 2
• Do NOT underdose vancomycin—ensure adequate serum trough levels of 15-20 μg/mL for CNS penetration 1

Duration and De-escalation

Continue empirical therapy until culture results and susceptibility testing are available 1. Once the pathogen is identified:

• For S. pneumoniae: Continue for 10-14 days; if penicillin-sensitive (MIC ≤0.06 mg/L), can switch to penicillin alone 3, 4
• For N. meningitidis: Continue ceftriaxone/cefotaxime for 5-7 days 3, 4
• For H. influenzae: Continue ceftriaxone/cefotaxime for 10 days 3, 4