What is the recommended empiric antibiotic and dexamethasone regimen for suspected bacterial meningitis in adults, children (including adolescents), and neonates, including dosing, duration, and adjustments for Listeria risk, viral meningitis, and tuberculous meningitis?

Treatment of Bacterial Meningitis

For suspected bacterial meningitis, initiate empiric antibiotics within 1 hour of presentation—immediately upon clinical suspicion—without waiting for lumbar puncture, imaging, or cerebrospinal fluid results, and administer adjunctive dexamethasone with or before the first antibiotic dose to reduce mortality and neurological sequelae. 1, 2, 3

Critical Timing Principles

• Start antibiotics within 60 minutes of hospital arrival; every delay beyond this window increases mortality and worsens neurological outcomes 2, 3, 4
• Never delay antibiotics for imaging or lumbar puncture—if CT is required (for focal deficits, new seizures, GCS <10, or severe immunocompromise), give antibiotics first, then obtain imaging 2, 3
• Obtain blood cultures before antibiotics but do not postpone treatment to acquire them 2, 3

Empiric Antibiotic Regimens by Age and Risk

Neonates (≤4 weeks)

Age <1 week:

• Ampicillin 50 mg/kg IV every 8 hours PLUS Cefotaxime 50 mg/kg IV every 8 hours PLUS Gentamicin 2.5 mg/kg IV every 12 hours 2, 3, 4
• Alternative aminoglycosides: Tobramycin 2.5 mg/kg IV every 8 hours or Amikacin 10 mg/kg IV every 8 hours 2

Age 1-4 weeks:

• Ampicillin 50 mg/kg IV every 6 hours PLUS Cefotaxime 50 mg/kg IV every 6-8 hours PLUS Gentamicin 2.5 mg/kg IV every 8 hours 2, 3, 4

Rationale: This combination covers Group B Streptococcus, Escherichia coli, and Listeria monocytogenes—the predominant neonatal pathogens 2, 4

Children (1 month to 18 years)

• Ceftriaxone 50 mg/kg IV every 12 hours (maximum 2 g per dose) OR Cefotaxime 75 mg/kg IV every 6-8 hours 2, 3, 5
• PLUS Vancomycin 10-15 mg/kg IV every 6 hours (target trough 15-20 µg/mL) 2, 3, 5
• Alternative in low-resistance settings: Rifampicin 10 mg/kg IV every 12 hours (maximum 600 mg/day) may replace vancomycin 2

Rationale: Covers Streptococcus pneumoniae (including resistant strains), Neisseria meningitidis, and Haemophilus influenzae 2, 3

Adults 18-50 Years (Immunocompetent)

• Ceftriaxone 2 g IV every 12 hours (or 4 g IV once daily) OR Cefotaxime 2 g IV every 4-6 hours 2, 3
• PLUS Vancomycin 15-20 mg/kg IV every 8-12 hours (target trough 15-20 µg/mL) 2, 3
• Alternative: Rifampicin 300 mg IV every 12 hours in low-resistance regions 2

Rationale: Targets S. pneumoniae (including resistant strains) and N. meningitidis, the most common adult pathogens 2, 3

Adults >50 Years OR Immunocompromised (Any Age)

• Ceftriaxone 2 g IV every 12 hours (or 4 g IV once daily) OR Cefotaxime 2 g IV every 4-6 hours 2, 3
• PLUS Vancomycin 15-20 mg/kg IV every 8-12 hours 2, 3
• PLUS Ampicillin 2 g IV every 4 hours (or Amoxicillin 2 g IV every 4 hours) 2, 3, 4

Rationale: Ampicillin is essential for Listeria monocytogenes coverage—cephalosporins have no activity against this pathogen 2, 3, 4

Listeria risk factors include:

• Age >50 years 2, 3
• Diabetes mellitus 2
• Immunosuppressive therapy (corticosteroids, chemotherapy, biologics) 2, 3
• Malignancy 2, 3
• Organ transplantation 2

Adjunctive Dexamethasone Therapy

Adults:

• Dexamethasone 10 mg IV every 6 hours for 4 days 1, 3

Children:

• Dexamethasone 0.15 mg/kg IV every 6 hours for 2-4 days 1, 3

Timing:

• Give dexamethasone with or 10-20 minutes before the first antibiotic dose to prevent inflammatory response from bacterial lysis 1, 3
• If omitted initially, can still be started up to 4 hours after antibiotics 1

Benefits:

• Reduces hearing loss and neurological sequelae in all bacterial meningitis 1
• Reduces mortality specifically in pneumococcal meningitis (14% vs 34%, P=0.02) 1, 3
• Most beneficial for S. pneumoniae and H. influenzae meningitis 1, 3

When to discontinue dexamethasone:

• Stop if bacterial meningitis is ruled out 1
• Stop if Listeria is identified—observational data show increased mortality with steroids in neurolisteriosis 4
• Consider stopping if N. meningitidis is confirmed, as benefit is unclear (though some experts continue regardless of pathogen) 1

Neonates:

• Dexamethasone is NOT recommended for neonates due to insufficient evidence 1

Pathogen-Specific Definitive Therapy (After Culture Results)

Pathogen	Susceptibility	Recommended Therapy	Duration
S. pneumoniae	Penicillin-sensitive (MIC <0.1 mg/L)	Penicillin G 24 million units/day IV divided every 4 hours OR continue ceftriaxone 2 g IV every 12 hours [2,3]	10-14 days [2,3]
	Penicillin-intermediate (MIC 0.1-1.0 mg/L)	Ceftriaxone 2 g IV every 12 hours OR cefotaxime 2 g IV every 6 hours [2]	10-14 days [2,3]
	Penicillin/cephalosporin-resistant (MIC ≥2 mg/L)	Vancomycin PLUS ceftriaxone (continue combination) [2,3]	10-14 days [2,3]
N. meningitidis	Penicillin-sensitive	Penicillin G 24 million units/day IV OR ceftriaxone 2 g IV every 12 hours [2,3]	5-7 days [2,3]
L. monocytogenes	—	Ampicillin 2 g IV every 4 hours (12 g/day total) OR amoxicillin 2 g IV every 4 hours [2,3]	21 days [2,3]
H. influenzae	—	Ceftriaxone 2 g IV every 12 hours OR cefotaxime 2 g IV every 6 hours [2,3]	10 days [2,3]
Gram-negative bacilli (e.g., E. coli, Klebsiella)	—	Ceftriaxone or cefotaxime PLUS aminoglycoside (gentamicin, tobramycin, or amikacin) [2,5]	14-21 days [2]

Regional Resistance Considerations

• In areas with high pneumococcal penicillin or cephalosporin resistance, always add vancomycin or rifampicin to third-generation cephalosporins 2, 3
• When true cephalosporin resistance (MIC >2 mg/L) is unlikely, some experts suggest ceftriaxone/cefotaxime alone, but adding vancomycin is recommended as a safety measure 2
• Animal studies show ceftriaxone combined with vancomycin or rifampicin achieves superior CSF sterilization versus ceftriaxone alone in resistant pneumococcal meningitis 2

Critical Pitfalls to Avoid

• Never delay antibiotics for imaging—give antibiotics first, then obtain CT if clinically indicated 2, 3, 6
• Never omit ampicillin in patients >50 years or immunocompromised—cephalosporins lack Listeria activity and omission can be fatal 2, 3, 4
• Never underdose—meningitis requires high-dose regimens to achieve adequate CSF penetration; standard dosing leads to treatment failure 2
• Never fail to obtain blood cultures before antibiotics, but do not let culture acquisition delay treatment beyond 1 hour 2, 3
• Never ignore local resistance patterns—adjust empiric therapy based on regional antimicrobial susceptibility data 2, 3

Special Considerations

Viral Meningitis

• Most cases are self-limited and require only supportive care 6
• If bacterial meningitis cannot be ruled out clinically, treat empirically as bacterial until CSF results confirm viral etiology 6

Tuberculous Meningitis

• Requires specialized multi-drug antituberculous therapy (isoniazid, rifampicin, pyrazinamide, ethambutol) plus cor