Meningitis%20-%20acute,%20bacterial Treatment

• Initial antibiotic therapy of purulent meningitis should be based on results of Gram stain or rapid bacterial antigen tests
• If lumbar puncture is delayed longer than 90-120 minutes or no etiologic agent can be identified, empiric therapy should be instituted
• Delay of antimicrobial therapy may be associated with adverse clinical outcomes especially if the patient has advanced to a high stage of prognostic severity
• Antimicrobial entry into the cerebrospinal fluid (CSF) decreases as inflammation subsides and permeability across the blood brain barrier decreases
  • Therefore, maximal parenteral doses of antibiotics should be continued throughout the course of therapy to maintain adequate CSF concentrations

Empiric Therapy for Patients with a Presumptive Cerebrospinal Fluid (CSF) Gram Stain

• Prompt initiation of therapy should be the standard of care
• Empiric antibiotic therapy should be directed to the most likely pathogens on the basis of the patient’s age and underlying health status
  • In general, antibiotics should be directed against N meningitidis, S aureus, and S pneumoniae
• Below is a list of the likely pathogens of acute bacterial meningitis in different groups of patients, depending on age/predisposing factors:

Considerations for Patients with Diagnostic Gram Stain Results

• A presumptive diagnosis may be made based on the results of the CSF Gram stain
• Modify treatment regimen for optimal therapy once culture and susceptibility results are available

S pneumoniae

• If culture is available, perform minimum inhibitory concentration (MIC) determination for S pneumoniae

H influenzae

• Testing for beta-lactamase production of H influenzae may also aid in tailoring the antibiotic regimen
  • 3rd- and 4th-generation cephalosporins, carbapenems, or Aztreonam may be used for beta-lactamase producing organisms

Antibiotic Therapy

• Exhibit synergistic activity with cell wall antibiotics eg penicillins, cephalosporins, monobactams and carbapenems
• Accumulation of CSF lactate in CSF during bacterial meningitis results in a decreased CSF pH, which may inhibit the bactericidal activity of this group of drugs
• Have inadequate penetration into the CSF, may have to be given intrathecally
• Consider adding Gentamicin to Ampicillin or Penicillin G in proven L monocytogenes meningitis

• May be used for meningitis due to aerobic Gram-negative bacilli
• Treatment option for patients with contraindications to beta-lactam antimicrobial agents or Meropenem

• Broad-spectrum cephalosporins used in meningitis include the 3rd-generation cephalosporins eg Cefotaxime, Ceftriaxone and 4th-generation cephalosporins eg Cefepime
• Cefotaxime or Ceftriaxone
  • Very active against streptococci and are usually effective against Penicillin-resistant strains but clinical failures have been reported
  • Drug of choice for patients with meningitis due to enteric Gram-negative bacilli
  • 3rd-generation cephalosporin eg Cefotaxime or Ceftriaxone may be used for N meningitidis with reduced susceptibility to Penicillin or as an alternative drug for S agalactiae
• Cefepime
  • Has been shown to be safe and therapeutically equivalent to Cefotaxime in the treatment of meningitis in infants and children
  • Has in vitro activity similar to that of Cefotaxime and Ceftriaxone against H influenzae, N meningitidis, and S pneumoniae and greater in vitro activity against Enterobacter sp and P aeruginosa
• Ceftazidime
  • Usually reserved for P aeruginosa (combine with aminoglycoside)

• Bacteriostatic antibiotic
• H influenzae, S pneumoniae and N meningitidis are highly susceptible
• Co-administration with a bacteriostatic agent, eg an aminoglycoside, may result in antagonism
• Has important toxic effects especially on the bone marrow (eg aplastic anemia)
  • Because of this, it is no longer the drug of choice for any specific infection

• An alternative drug for a patient with L monocytogenes meningitis and Penicillin allergy

• Ampicillin or Penicillin
  • Ampicillin and Penicillin G are the drugs of choice for N meningitidis and L monocytogenes meningitis
  • These recommendations may change as the trends of antimicrobial susceptibility of meningococci change

• Ampicillin
  • Ampicillin combined with an aminoglycoside is the standard therapy for S agalactiae and L monocytogenes meningitis
  • The drug combination is synergistic and effective against Penicillin-tolerant strains

• Penicillin G
  • The drug of choice for susceptible isolates of S pneumoniae and Propionibacterium acnes infection

• Antistaphylococcal Penicillins
  • Nafcillin or Oxacillin should be used to treat Methicillin-susceptible S aureus (MSSA) meningitis

• May be used for meningitis caused by Penicillin-resistant S pneumoniae or by aerobic Gram-negative bacilli including P aeruginosa
  • Pneumococcal strains that are highly resistant to penicillins and cephalosporins may also be resistant to Meropenem
• First-line therapy for infections caused by Ceftazidime-resistant Gram-negative bacilli eg extended spectrum beta-lactamase-producing organisms, Acinetobacter spp 
• Has been shown to have clinical and microbiologic outcomes similar to Cefotaxime and Ceftriaxone and may be considered as an alternative to these agents
• Has less seizure proclivity than Imipenem

• Ciprofloxacin has been used successfully in some patients with Gram-negative meningitis
• Moxifloxacin may be considered for patients with contraindications to Penicillin therapy
• Combination with a 3rd-generation cephalosporin or Vancomycin is recommended

• May be added to Vancomycin in the treatment of the following:
  • Meningitis caused by Penicillin-resistant S pneumoniae when the organism is demonstrated to be susceptible and the expected clinical or bacteriologic response is delayed
  • Meningitis due to coagulase-negative staphylococci or Methicillin-resistant S aureus (MRSA) when patient fails to improve with Vancomycin alone
  • CSF shunt infections caused by Staphylococci, especially when shunt cannot be removed

• Empiric therapy in an area of high prevalence of Penicillin-resistant S pneumoniae should consist of a combination of Vancomycin plus a 3rd-generation cephalosporin
  • Vancomycin should never be used alone in the treatment of pneumococcal meningitis
• Recommended for meningitis caused by MRSA or coagulase-negative staphylococci and is considered an alternative drug for patients with Penicillin allergy and Methicillin-susceptible S aureus (MSSA) meningitis
• Concomitant administration of Dexamethasone results in decreased brain inflammation and poor entry of Vancomycin into the CSF
• Consider intrathecal administration in patients not responding to IV administration

• Duration of therapy has been based more on tradition than on scientific evidence
  • 7-10 days for H influenzae
  • 7 days for N meningitidis
  • 10-14 days for S pneumoniae
  • 14-21 days for Group B streptococci (eg S agalactiae)
  • 21 days for aerobic Gram-negative bacilli (in the neonate, duration is 2 weeks beyond 1st sterile CSF culture or for 3 weeks whichever is longer)
  • ≥21 days for L monocytogenes
• Some patients may require longer courses of antibiotic therapy; therefore, treatment must always be individualized
  • Longer courses for complicated meningitis such as subdural empyema, ventriculitis, brain abscess, suppurative venous sinus thrombosis
• IV administration of antibiotic is recommended for the duration of treatment to ensure adequate CSF concentrations of specific antimicrobial agents are achieved

Pathogen Specific Therapy

• If culture results are positive, tailor treatment regimen based on the results
• If test is available, perform minimum inhibitory concentration (MIC) determination for S pneumoniae
• Alternative regimens may be used in case of allergy to the recommended drug
  

• Adjunctive therapy includes anti-inflammatory therapy, agents to reduce the intracranial pressure (ICP) and anticonvulsants

• Action: Significantly reduces synthesis of proinflammatory cytokines, attenuates subarachnoid space inflammatory response and ameliorates meningeal inflammatory indices
• Should be started by IV route 10-20 minutes before or at the same time as the first dose of antibiotic
  • Benefit is uncertain when dexamethasone is administered ≥1 hour after the 1st antibiotic dose
• Use in children
  • Dexamethasone is recommended in previously well and non-immunocompromised infants and children with clinically suspected bacterial meningitis caused by H influenzae and S pneumoniae (eg early focal neurologic signs are present)
• Use in adults
  • Adjunctive Dexamethasone is recommended in previously well and non-immunocompromised adults with clinically suspected or known pneumococcal meningitis
  • Dexamethasone should be continued only if the CSF Gram stain shows Gram-positive cocci in pairs, chains or scattered singly or if blood or CSF cultures are positive for S pneumoniae
• Precautions
  • By decreasing brain inflammation, Dexamethasone may reduce the penetration of antibiotic into the CSF, particularly Vancomycin, and this may result in delayed sterilization of the CSF
  • Patients who are given Dexamethasone must be closely monitored for evidence of gastrointestinal (GI) blood loss; addition of histamine-2 antagonists is recommended to decrease the risk of gastrointestinal bleeding
• Dosage
  • Adults: 10 mg IV 6 hourly for 4 days
  • Infants and children: 0.15 mg/kg/dose IV 6 hourly for 4 days
    • May also be an alternative dose for patients with low body weight or increased risk for side effects with corticosteroids

• The following agents (except Dexamethasone) have not been studied in clinical trials in patients with meningitis

• As above

• Action: Mannitol is a hyperosmolar agent that makes the intravascular space hyperosmolar to the brain and permits movement of water from brain tissue into the intravascular compartment
• Dosage: 1-1.5 g/kg IV given over 15 minutes; may repeat once

• Eg Phenobarbital 
• Barbiturates may be considered in patients with continued elevated ICP after other measures have failed
• Action: Decreases cerebral metabolic demands and cerebral blood flow

• May be considered for decreasing ICP
• Use with caution as rapid lowering of blood pressure may cause compromise in intracranial perfusion and cause brain injury

• Eg Diazepam, Lorazepam, Phenytoin
• Administer if patient has seizures
• Diazepam or Lorazepam may be given for immediate treatment of seizures at the following dosages:
  • Diazepam (10-20 mg rectally)
  • Lorazepam (0.1 mg/kg/dose IV)
• Phenytoin may be given to reduce likelihood of recurrence at 15-18 mg/kg loading dose

• Patients with signs of increased ICP (eg changes in level of consciousness, nonreactive or poorly reactive pupils, ocular movement disorders) and who are comatose or are stuporous may benefit from ICP monitoring
• ICP >20 mmHg should be treated
• Consider treating ICP >15 mmHg to avoid larger elevations that can lead to cerebral herniation and brain stem injury

• Elevation of head of the bed (30-45 degrees) to maximize venous drainage with minimum compromise of cerebral perfusion
• Hyperventilation to cause cerebral vasoconstriction and reduction in cerebral blood volume
  • Be cautious with this maneuver as it may exacerbate focal cerebral ischemia
• An intraventricular shunt with cerebrospinal fluid (CSF) drainage may be needed when there is evidence of hydrocephalus
  • The need to perform this procedure depends on patient’s level of consciousness and degree of ventricular dilatation as seen on brain imaging