Among adults with bacterial meningitis in the United States, Streptococcus pneumoniae and Neisseria meningitidis are the most common infecting organisms.
●Antimicrobial selection must be empiric immediately after cerebrospinal fluid (CSF) is obtained or when lumbar puncture is delayed. In such patients, antimicrobial therapy needs to be directed at the most likely bacteria based upon patient age and underlying comorbid disease．
We recommend that antimicrobial therapy be initiated immediately after the performance of the lumbar puncture (LP) or, if a computed tomography (CT) scan of the head is to be performed before LP, immediately after blood cultures are obtained (Grade 1B). Adjunctive dexamethasone should be given shortly before or at the same time as the first dose of antimicrobials, when indicated.
For adults in the developed world with suspected bacterial meningitis in whom the organism is unknown or Streptococcus pneumoniae is confirmed, we recommend administration of dexamethasone (Grade 1B). Dexamethasone should be continued if the CSF Gram stain and/or the CSF or blood cultures reveal S. pneumoniae. The indications for dexamethasone in patients in the developing world with suspected or confirmed bacterial meningitis are less certain and are discussed in detail elsewhere. Rifampin is added to the regimen in patients receiving dexamethasone under certain circumstances.
Rather than empiric therapy, antimicrobials should be directed at the presumed pathogen if the Gram stain is diagnostic．
The antimicrobial regimen should be modified further, when indicated, based on the CSF culture and susceptibility results．
Because of the general limitation in antimicrobial penetration into the CSF, all patients should be treated with intravenous (IV) antimicrobials.
●For the initial therapy of S. pneumoniae, we recommend vancomycin plus either ceftriaxone or cefotaxime rather than a third-generation cephalosporin alone (Grade 1B).
The dosing for patients with normal renal function is:
•Vancomycin – 15 to 20 mg/kg IV every 8 to 12 hours (not to exceed 2 g per dose or a total daily dose of 60 mg/kg; adjust dose to achieve vancomycin serum trough concentrations of 15 to 20 mcg/mL)
•Ceftriaxone – 2 g IV every 12 hours
•Cefotaxime – 2 g IV every four to six hours
If the isolate is susceptible to third-generation cephalosporins (minimal inhibitory concentration [MIC] <1.0 mcg/mL), vancomycin should be discontinued.
For the initial therapy of N. meningitidis, we recommend a third-generation cephalosporin, such as cefotaxime or ceftriaxone, rather than penicillin, while awaiting susceptibility data (Grade 1C)． If the isolate is susceptible to penicillin, either a third-generation cephalosporin or penicillin may be used to complete the course of therapy
The preferred regimens for other causes of bacterial meningitis are discussed above
The optimal regimens for patients with severe drug allergies depends upon the organism.
●Vaccines against N. meningitidis and S. pneumoniae are recommended for adults at increased risk of these infections.
●There is a role for postexposure chemoprophylaxis to prevent spread of meningococcal and Haemophilus meningitis under certain circumstances．