Abx, meningitis, doc

Neonates (< 1 month)

Common Pathogens: S. agalactiae (GBS), E. coli, Listeria monocytogenes

First-Line Empirical Regimen: Ampicillin + Cefotaxime (or Gentamicin)

High-Yield PHLE Board Pearls: Never give Ceftriaxone to neonates. It displaces bilirubin from albumin (causing kernicterus) and precipitates with calcium into biliary sludge.

1 mo to 50 yrs

Common Pathogens: N. meningitidis, S. pneumoniae

First-Line Empirical Regimen: Ceftriaxone (or Cefotaxime) + Vancomycin

High-Yield PHLE Board Pearls: Vancomycin is added to ensure coverage against penicillin-resistant strains of S. pneumoniae.

Adults > 50 yrs / Immunocompromised

Common Pathogens: S. pneumoniae, N. meningitidis, Listeria monocytogenes

First-Line Empirical Regimen: Ceftriaxone + Vancomycin + Ampicillin

High-Yield PHLE Board Pearls: Ampicillin is added specifically for Listeria. Cephalosporins have zero coverage against Listeria monocytogenes.

Post-Neurosurgery / Head Trauma

Common Pathogens: Pseudomonas aeruginosa, S. aureus, Gram-negative bacilli

First-Line Empirical Regimen: Cefepime (or Meropenem) + Vancomycin

High-Yield PHLE Board Pearls: Broad coverage requiring anti-pseudomonal $\beta$-lactam activity plus MRSA coverage.

Streptococcus pneumoniae

Ceftriaxone + Vancomycin (de-escalate to Penicillin G if susceptible).

Neisseria meningitidis

Penicillin G or Ceftriaxone.

Listeria monocytogenes

Ampicillin (or Penicillin G) ± Gentamicin

Haemophilus influenzae

Ceftriaxone or Cefotaxime

Pseudomonas aeruginosa

Cefepime, Ceftazidime, or Meropenem.

Dexamethasone Co-administration

Must be given 10 to 20 minutes before or concurrently with the first dose of antibiotics in S. pneumoniae (and H. influenzae in children). It blunts the severe inflammatory response triggered by antibiotic-induced bacterial lysis, reducing neurological sequelae like sensorineural hearing loss.

Post-Exposure Prophylaxis

Close contacts of individuals with N. meningitidis should receive prophylaxis with Rifampin, Ciprofloxacin (single oral dose), or Ceftriaxone (single IM dose).

Blood-Brain Barrier (BBB) Penetration

Inflammation increases BBB permeability, allowing high doses of hydrophilic drugs (like Ceftriaxone, Cefotaxime, and Vancomycin) to reach therapeutic levels in the cerebrospinal fluid (CSF).

CSF Differential Analysis

_{^{Board exams frequently test your ability to identify the etiology of meningitis based on Cerebrospinal Fluid (CSF) lumbar puncture results.}}

Opening Pressure

Predominant Cell

WBC Count

Protein Level

Glucose Level

Opening Pressure

Normal CSF: 80–200 mm H2O

Bacterial Meningitis: mm H2O Elevated (>200 mm H2O)

Viral Meningitis: Normal or Slightly Elevated

Fungal / TB Meningitis: Elevated

Predominant Cell

Normal CSF: Monocytes / Lymphocytes

Bacterial Meningitis: Neutrophils (PMNs) (>80%)

Viral Meningitis: Lymphocytes

Fungal / TB Meningitis: Lymphocytes

WBC Count

Normal CSF:0–5 cells/mu L

Bacterial Meningitis: Markedly High (>1,000)

Viral Meningitis: Moderately High (10–500)

Fungal / TB Meningitis: Moderately High (50–500)

Protein Level

Normal CSF: 15–45 mg/dL

Bacterial Meningitis: Markedly High (>100–500)

Viral Meningitis: Normal or Mildly High

Fungal / TB Meningitis: Markedly High (>100)

Glucose Level

Normal CSF: 50–80 mg/dL (2/3 of serum)

Bacterial Meningitis: Markedly Low (<40 mg/dL)

Viral Meningitis :Normal

Fungal / TB Meningitis: Markedly Low (<40 mg/dL)

Indication

Recommended primarily in adults with suspected or confirmed S. pneumoniae meningitis, and infants/children with H. influenzae type b.

Timing

Must be administered 10 to 20 minutes before or concurrently with the first dose of IV antibiotics

Rationale

Rapid bacterial lysis induced by antibiotics releases cell wall components (peptidoglycans, endotoxins) into the CSF, triggering a massive, destructive inflammatory response. Dexamethasone blunts this cytokine cascade, reducing mortality and preventing sensorineural hearing loss and neurological complications.

PHLE Board Pearl

If given after antibiotics have already been administered, dexamethasone provides no clinical benefit.

Neisseria meningitidis Prophylaxis Options

• Rifampin: 600 mg PO BID for 2 days. (High-yield side effect: Harmless orange-red discoloration of body fluids including tears, urine, and sweat; stains contact lenses).

• Ciprofloxacin: 500 mg PO as a single dose. (Avoid in pediatric patients if alternatives are available).

• Ceftriaxone: 250 mg IM as a single dose. (Drug of Choice in pregnant women requiring prophylaxis).

Haemophilus influenzae type b (Hib) Prophylaxis

Rifampin: 600 mg PO once daily for 4 days.