Empiric Treatment of Suspected Acute Bacterial Meningitis
Antibiotics must be administered within 1 hour of hospital arrival and should never be delayed for lumbar puncture or head CT. 1
Immediate Actions (Within First Hour)
Step 1: Draw Blood Cultures Immediately
- Obtain blood cultures before antibiotics, but do not delay treatment beyond 1 hour 1
- Blood cultures remain positive in 71% of cases even when CSF cultures are negative 2
Step 2: Determine Need for Head CT Before Lumbar Puncture
Perform urgent head CT before LP only if ANY of the following are present: 1
- Focal neurologic deficits (excluding cranial nerve palsies alone)
- New-onset seizures (within past week)
- Severely altered mental status (Glasgow Coma Scale <10)
- Severely immunocompromised state
- History of CNS mass lesion or stroke
- Papilledema
If none of these features are present, proceed directly to LP without imaging. 1
Step 3: Start Empiric Antibiotics + Dexamethasone
Give antibiotics immediately after blood cultures, regardless of whether LP has been performed. 1
Age-Specific Empiric Antibiotic Regimens
Neonates (<1 Month Old)
Ampicillin PLUS Cefotaxime (or Ampicillin PLUS Aminoglycoside) 1
Dosing:
Age <1 week:
- Ampicillin 50 mg/kg IV q8h
- Cefotaxime 50 mg/kg IV q8h
- Gentamicin 2.5 mg/kg IV q12h 1
Age 1-4 weeks:
- Ampicillin 50 mg/kg IV q6h
- Cefotaxime 50 mg/kg IV q6-8h
- Gentamicin 2.5 mg/kg IV q8h 1
Children (1 Month to 18 Years)
Ceftriaxone (or Cefotaxime) PLUS Vancomycin 1, 3
Dosing:
- Ceftriaxone 50 mg/kg IV q12h (maximum 2 g q12h)
- Cefotaxime 75 mg/kg IV q6-8h
- Vancomycin 10-15 mg/kg IV q6h (target trough 15-20 μg/mL) 1
Adults 18-50 Years (Immunocompetent)
Ceftriaxone (or Cefotaxime) PLUS Vancomycin 1, 3
Dosing:
- Ceftriaxone 2 g IV q12h (or 4 g IV q24h)
- Cefotaxime 2 g IV q4-6h
- Vancomycin 15-20 mg/kg IV q8-12h (target trough 15-20 μg/mL) 1, 3
Adults >50 Years OR Immunocompromised (Any Age)
Ceftriaxone (or Cefotaxime) PLUS Vancomycin PLUS Ampicillin 1, 3
Dosing:
- Ceftriaxone 2 g IV q12h
- Vancomycin 15-20 mg/kg IV q8-12h (target trough 15-20 μg/mL)
- Ampicillin 2 g IV q4h (for Listeria coverage) 1, 3
Risk factors requiring Listeria coverage: age >50, diabetes mellitus, immunosuppressive drugs, cancer, organ transplant, chronic liver disease, pregnancy 1, 3
Adjunctive Dexamethasone Therapy
Dexamethasone 10 mg IV should be given immediately before or simultaneously with the first antibiotic dose. 3, 4
Dosing schedule:
Continue dexamethasone if pneumococcal meningitis is confirmed or probable; discontinue if another pathogen is identified. 3
Beta-Lactam Allergy Alternatives
For Severe Penicillin/Cephalosporin Allergy (Type I Hypersensitivity)
Replace ceftriaxone/cefotaxime with:
- Moxifloxacin 400 mg IV q24h (covers pneumococcus and most gram-negatives)
- PLUS Vancomycin (as dosed above)
- PLUS Trimethoprim-sulfamethoxazole 5 mg/kg IV q6-12h (if Listeria coverage needed) 1
Alternative for Listeria coverage in beta-lactam allergy:
- Trimethoprim-sulfamethoxazole 5 mg/kg (based on TMP component) IV q6-12h 1
Note: Aztreonam may be used for gram-negative coverage in beta-lactam allergy but does NOT cover gram-positives or Listeria 1
Critical Timing Considerations
Antibiotic Administration Relative to Lumbar Puncture
Three clinical scenarios:
No CT indication present: Draw blood cultures → Perform LP immediately → Start antibiotics within 1 hour of arrival 1
CT indicated but no antibiotics yet given: Draw blood cultures → Start antibiotics immediately → Perform CT → Perform LP only if CT shows no mass effect 1
Antibiotics already given before LP: CSF culture yield decreases but LP remains valuable:
The delay in antibiotic treatment is strongly associated with death and poor neurological outcomes—never delay antibiotics for diagnostic procedures. 1, 6
Common Pitfalls to Avoid
Pitfall 1: Delaying Antibiotics for Imaging
60% of patients inappropriately receive CT before LP, causing treatment delays. 6, 7 Most patients do not meet criteria for pre-LP imaging 1. Start antibiotics immediately if CT is required. 1
Pitfall 2: Inadequate Listeria Coverage
Listeria occurs in 1.5% of adults <50 years without risk factors, but is common in those >50 years or immunocompromised. 1 Ceftriaxone and vancomycin do NOT cover Listeria—ampicillin must be added 1, 3
Pitfall 3: Subtherapeutic Vancomycin Dosing
Vancomycin must achieve CSF trough concentrations of 15-20 μg/mL. 1 Standard dosing is 15-20 mg/kg IV q8-12h, not the lower doses used for other infections 1
Pitfall 4: Assuming Negative Cultures Rule Out Bacterial Meningitis
CSF cultures become negative within 2-4 hours of antibiotics, but CSF parameters (elevated WBC, low glucose, high protein) remain abnormal. 5 Use CSF PCR and blood cultures to confirm diagnosis in partially treated cases 5
Pitfall 5: Omitting Dexamethasone
Dexamethasone reduces mortality and neurological morbidity in pneumococcal meningitis and must be given with or before the first antibiotic dose. 3, 4 Efficacy is lost if given >12 hours after antibiotics 3
Pitfall 6: Assuming Normal CSF Rules Out Bacterial Meningitis
Bacterial meningitis can present with minimal or absent pleocytosis early in illness, and mortality in such cases is high. 2 Treat empirically based on clinical suspicion even if initial CSF is equivocal 2
Summary Algorithm
Suspected Bacterial Meningitis
↓
Draw Blood Cultures
↓
Assess for CT Indications:
• Focal deficits (not CN palsies)
• New seizure
• GCS <10
• Immunocompromised
• CNS mass/stroke history
• Papilledema
↓
┌────┴────┐
NO YES
↓ ↓
Immediate LP Start Antibiotics + Dexamethasone
↓ ↓
Start Rx CT scan
within 1 hr ↓
LP if safe
↓
Age-Specific Empiric Regimen:
• <1 mo: Ampicillin + Cefotaxime
• 1 mo-18 yr: Ceftriaxone + Vancomycin
• 18-50 yr: Ceftriaxone + Vancomycin
• >50 yr or immunocompromised:
Ceftriaxone + Vancomycin + Ampicillin
↓
Dexamethasone 10 mg IV q6h × 4 days