Treatment of Suspected Bacterial Meningitis with Pachymeningeal and Leptomeningeal Enhancement
Initiate empirical antibiotic therapy immediately—within 1 hour of clinical suspicion—with a third-generation cephalosporin (ceftriaxone 2g IV every 12 hours or cefotaxime 2g IV every 6 hours) plus vancomycin (15-20 mg/kg IV every 12 hours), and add ampicillin 2g IV every 4 hours if the patient is ≥60 years old or immunocompromised to cover Listeria monocytogenes. 1, 2
Immediate Management Priorities
Time is critical—delays in antibiotic administration directly increase mortality and neurological morbidity. 1, 2
- Obtain blood cultures immediately before antibiotics, but do not delay treatment waiting for lumbar puncture or imaging 1, 2
- If lumbar puncture cannot be performed within 1 hour, start antibiotics after blood cultures and perform LP as soon as possible thereafter (preferably within 4 hours of antibiotic initiation) 2
- The imaging findings described (pachymeningeal and leptomeningeal enhancement) are consistent with meningitis and warrant immediate empirical treatment 2
Empirical Antibiotic Regimen Selection
For adults <60 years without risk factors:
- Ceftriaxone 2g IV every 12 hours OR cefotaxime 2g IV every 6 hours 2, 1
- PLUS vancomycin 15-20 mg/kg IV every 12 hours 2, 1
For adults ≥60 years or immunocompromised patients:
- Same cephalosporin regimen as above 2, 1
- PLUS vancomycin 15-20 mg/kg IV every 12 hours 2, 1
- PLUS ampicillin 2g IV every 4 hours (to cover Listeria monocytogenes) 2, 1
The rationale: Third-generation cephalosporins have excellent CSF penetration and cover Streptococcus pneumoniae and Neisseria meningitidis, the most common pathogens. 2 Vancomycin is added empirically due to increasing pneumococcal resistance to penicillin and cephalosporins. 2, 1 Ampicillin covers Listeria, which becomes increasingly common after age 50 and in immunocompromised states. 2, 1
Special Considerations for Antibiotic Resistance
If recent travel to areas with high penicillin-resistant pneumococcal rates:
- Add rifampicin 600mg IV/PO every 12 hours to the above regimen 2
- Check European Centre for Disease Prevention and Control or WHO databases for current resistance patterns 2
If penicillin allergy:
- Use chloramphenicol 25 mg/kg IV every 6 hours as alternative to cephalosporins 2
- Continue vancomycin and ampicillin (if indicated) 2
Adjunctive Dexamethasone Therapy
Administer dexamethasone 0.15 mg/kg IV every 6 hours for 2-4 days, given 10-20 minutes before or with the first antibiotic dose. 2
- Dexamethasone reduces mortality and neurological sequelae (particularly hearing loss) in adults with pneumococcal meningitis 2
- Must be given before or simultaneously with antibiotics to be effective—not beneficial if started after antibiotics 2
- The benefit is most pronounced for pneumococcal meningitis, which is the most common cause in adults 2
Critical Pitfalls to Avoid
Do not delay antibiotics for imaging or lumbar puncture—bacterial meningitis is a neurologic emergency where every hour of delay worsens outcomes. 1, 2 Start treatment on clinical suspicion after obtaining blood cultures. 1, 2
Do not omit ampicillin coverage in patients ≥60 years or immunocompromised—Listeria monocytogenes is not covered by cephalosporins and is increasingly common in these populations. 1, 2 Risk factors include age >50, diabetes, immunosuppressive drugs, cancer, and chronic illness. 1
Do not use inadequate dosing—meningitis requires high-dose antibiotics to achieve adequate CSF penetration. 1 Standard doses are: ceftriaxone 2g every 12 hours (not the typical 1g daily used for other infections), vancomycin 15-20 mg/kg every 12 hours, and ampicillin 2g every 4 hours. 2, 3
Do not forget dexamethasone—if bacterial meningitis is suspected, dexamethasone should be given before or with the first antibiotic dose, not hours later. 1, 2
Duration and Adjustment of Therapy
Once culture results and sensitivities return, narrow therapy to the most appropriate targeted antibiotic. 2