Current pharmacotherapy of pneumococcal meningitis

Comparison of the probability of target attainment between ceftriaxone and cefepime in the cerebrospinal fluid and serum against Streptococcus pneumoniae

Although the disposition of ceftriaxone and cefepime in the cerebrospinal fluid (CSF) has been described, the ability of these agents to achieve critical pharmacodynamic targets against Streptococcus pneumoniae in CSF has not been reported. Plasma and CSF pharmacokinetic data were obtained from hospital patients with external ventricular drains and receiving ceftriaxone or cefepime. Concentration-time profiles in plasma and CSF were modeled using a 3-compartment model with 0-order infusion and 1st-order elimination and transfer. The model parameters were identified with population pharmacokinetic analysis (Big Non-Parametric Adaptive Grid with adaptive gamma). A Monte Carlo Simulation (9999 subjects) estimated the probability of target attainment (PTA) for total drug CSF concentrations at 50% and 100% T>MIC for ceftriaxone 2G IV Q12H and cefepime 2G IV Q8H. The S. pneumoniae bloodstream infection isolates from the SENTRY Antimicrobial Surveillance Program (USA) provided the distribution of contemporary (2003-2004) MICs. Post-Bayesian measures of bias and precision, observed-predicted plots, and R2 values were highly acceptable for both drugs. The probabilities of achieving 50% and 100% T>MIC in the CSF for ceftriaxone were 76% and 65%, respectively. For cefepime, the PTA at 50% and 100% T>MIC in the CSF were 91.8% and 82%, respectively. The CSF pharmacodynamics against S. pneumoniae for cefepime were superior to that of ceftriaxone. The implications of these findings need to be reexamined in the clinical setting.

Aquaporin-4 gene disruption in mice reduces brain swelling and mortality in pneumococcal meningitis

The astroglial water channel aquaporin-4 (AQP4) facilitates water movement into and out of brain parenchyma. To investigate the role of AQP4 in meningitis-induced brain edema, Streptococcus pneumoniae was injected into cerebrospinal fluid (CSF) in wild type and AQP4 null mice. AQP4-deficient mice had remarkably lower intracranial pressure (9 +/- 1 versus 25 +/- 5 cm H2O) and brain water accumulation (2 +/- 1 versus 9 +/- 1 microl) at 30 h, and improved survival (80 versus 0% survival) at 60 h, through comparable CSF bacterial and white cell counts. Meningitis produced marked astrocyte foot process swelling in wild type but not AQP4 null mice, and slowed diffusion of an inert macromolecule in brain extracellular space. AQP4 protein was strongly up-regulated in meningitis, resulting in a approximately 5-fold higher water permeability (P(f)) across the blood-brain barrier compared with non-infected wild type mice. Mathematical modeling using measured P(f) and CSF dynamics accurately simulated the elevated lower intracranial pressure and brain water produced by meningitis and predicted a beneficial effect of prevention of AQP4 upregulation. Our findings provide a novel molecular mechanism for the pathogenesis of brain edema in acute bacterial meningitis, and suggest that inhibition of AQP4 function or up-regulation may dramatically improve clinical outcome.

Clinical features and prognostic factors in adults with bacterial meningitis

BACKGROUND

We conducted a nationwide study in the Netherlands to determine clinical features and prognostic factors in adults with community-acquired acute bacterial meningitis.

METHODS

From October 1998 to April 2002, all Dutch patients with community-acquired acute bacterial meningitis, confirmed by cerebrospinal fluid cultures, were prospectively evaluated. All patients underwent a neurologic examination on admission and at discharge, and outcomes were classified as unfavorable (defined by a Glasgow Outcome Scale score of 1 to 4 points at discharge) or favorable (a score of 5). Predictors of an unfavorable outcome were identified through logistic-regression analysis.

RESULTS

We evaluated 696 episodes of community-acquired acute bacterial meningitis. The most common pathogens were Streptococcus pneumoniae (51 percent of episodes) and Neisseria meningitidis (37 percent). The classic triad of fever, neck stiffness, and a change in mental status was present in only 44 percent of episodes; however, 95 percent had at least two of the four symptoms of headache, fever, neck stiffness, and altered mental status. On admission, 14 percent of patients were comatose and 33 percent had focal neurologic abnormalities. The overall mortality rate was 21 percent. The mortality rate was higher among patients with pneumococcal meningitis than among those with meningococcal meningitis (30 percent vs. 7 percent, P<0.001). The outcome was unfavorable in 34 percent of episodes. Risk factors for an unfavorable outcome were advanced age, presence of otitis or sinusitis, absence of rash, a low score on the Glasgow Coma Scale on admission, tachycardia, a positive blood culture, an elevated erythrocyte sedimentation rate, thrombocytopenia, and a low cerebrospinal fluid white-cell count.

CONCLUSIONS

In adults presenting with community-acquired acute bacterial meningitis, the sensitivity of the classic triad of fever, neck stiffness, and altered mental status is low, but almost all present with at least two of the four symptoms of headache, fever, neck stiffness, and altered mental status. The mortality associated with bacterial meningitis remains high, and the strongest risk factors for an unfavorable outcome are those that are indicative of systemic compromise, a low level of consciousness, and infection with S. pneumoniae.