A 22-year-old male presents to the emergency department with a 12-hour history of severe headache, high fever (39.8°C), and neck stiffness. On examination, he has a positive Kernig sign and Brudzinski sign. A petechial rash is noted on his trunk and lower extremities. CSF analysis shows: WBC 450/μL (90% neutrophils), protein 180 mg/dL, glucose 25 mg/dL (serum glucose 95 mg/dL). Gram stain of CSF shows gram-negative diplococci. Which of the following is the most appropriate initial antibiotic therapy?

Explanation

## Clinical Diagnosis **Key Point:** This patient has meningococcal meningitis caused by *Neisseria meningitidis*, evidenced by the classic triad of fever, headache, and neck stiffness with petechial rash (meningococcemia). ## CSF Analysis Interpretation | Parameter | Value | Interpretation | |-----------|-------|----------------| | WBC count | 450/μL (90% PMN) | Bacterial meningitis | | Protein | 180 mg/dL | Elevated (bacterial pattern) | | Glucose | 25 mg/dL (CSF:serum ratio ~0.26) | Low (bacterial meningitis) | | Gram stain | Gram-negative diplococci | *Neisseria* species | ## Antibiotic Selection **High-Yield:** Ceftriaxone is the first-line empiric agent for bacterial meningitis in adults because: 1. Excellent CNS penetration (achieves therapeutic CSF levels) 2. Covers *N. meningitidis*, *S. pneumoniae*, and *L. monocytogenes* (when combined with ampicillin in age >50 or immunocompromised) 3. Superior CSF concentrations compared to penicillin G 4. Preferred over penicillin even for penicillin-susceptible meningococci due to higher CSF levels **Clinical Pearl:** Although penicillin G was historically used for meningococcal meningitis, cephalosporins (ceftriaxone or cefotaxime) are now preferred because they achieve higher CSF concentrations and provide broader empiric coverage while awaiting culture results. **Mnemonic:** **CRAB** = Cephalosporin for meningitis (Ceftriaxone/Cefotaxime), Respiratory fluoroquinolones for pneumonia, Aminoglycosides for gram-negatives in other sites, Beta-lactams for meningitis. ## Dosing in Meningitis **Key Point:** High-dose ceftriaxone is mandatory for meningitis: **2 g IV every 12 hours** (or 1 g every 6 hours) to achieve adequate CSF penetration. ## Adjunctive Therapy - Dexamethasone 10 mg IV 6-hourly × 4 days (reduces mortality and hearing loss) - Initiate before or with first antibiotic dose - Reduces CSF inflammation and improves antibiotic penetration