In recent years, many reports have documented an increasing incidence of pneumococcal isolates that have a relatively high resistance to penicillin, reaching 50 percent in some European countries. Current estimates are that, in some areas of the United States, 15 percent of these isolates are penicillin-resistant to some degree (most have a relatively low level of resistance). In the 1970s, H. influenzae type B strains producing beta-lactamase, which are resistant to ampicillin and penicillin, were recognized. Currently, 30 percent of H. influenzae isolates produce the beta-lactamase enzyme, but almost all remain sensitive to third-generation cephalosporins (e.g., cefotaxime, ceftizoxime, ceftriaxone).
Recommendations for the institution of empiric treatment of meningitis have been reviewed by van de Beek and colleagues (2006) and by McGill and colleagues, often updated, often requiring updating and are summarized in modified form in Table 31-2. The choice of agents evolves based on epidemiology, patterns of resistance and geographic region, but the ones given here are a good approximation to current practice in developed countries.
In children and adults, third-generation cephalosporins such as ceftriaxone, combined with vancomycin is probably the best initial therapy for the three major types of community-acquired meningitides. In areas with low numbers of high-level penicillin-resistant pneumococci, it is possible to avoid adding vancomycin. Ampicillin should be added to the regimen in cases of suspected Listeria meningitis, particularly in an immunocompromised patient. Intravenous drug abusers have high rates of meningitis due to S. Aureus and should receive cefepime or ceftazidime with vancomycin. When serious allergy to penicillin and cephalosporins precludes their use, chloramphenicol may be a suitable alternative in some regions, but not for Listeria.
Isolation from the blood or CSF of a resistant organism requires the use of ceftriaxone with the addition of vancomycin and rifampin. N. meningitidis, at least in the United States, remains highly susceptible to penicillin and ampicillin. Regional variations and ongoing antibiotic-induced changes in the infecting microorganisms underscore the need for constant awareness of drug resistance in the physician’s local area, especially in the case of pneumococcal infections. Throughout the course of treatment, it is necessary to have access to a laboratory that can carry out rapid and detailed drug-resistance testing.
Nosocomial meningitis In cases of meningitis caused by coagulase-positive S. aureus, including those that occur after neurosurgery or major head injury, administration of vancomycin plus a third-generation cephalosporin (e.g., cefepime, ceftazadime, or meropenem) is a reasonable first approach. If Pseudomonas is considered possible, such as after neurosurgery, an antipseudomonal cephalosporin such as ceftazidime or cefepime should be added. Once the sensitivity of the organism has been determined, therapy may have to be altered or may be simplified by using vancomycin or nafcillin alone. These approaches have been reviewd by van de Beek and colleagues (2010). They note that the CSF cell count may be low in cases of ventricular catheter-associated meningitis. They also provide recommendations on the use of prophylactic antibiotics after a basilar skull fracture, a controversial problem that is reviewed in Chap. 34.
Table 31-3 lists the approximate dosages of the most used antibiotics, and Table 31-4 gives reasonable choices of antibiotic for the treatment of specific bacterial isolates.