Antibacterial agents in infections of the central nervous system

Role of rifampin for the treatment of bacterial infections other than mycobacteriosis

OBJECTIVES

Rifampin was initially approved for the treatment of tuberculosis. Because of its low toxicity, broad-spectrum activity, and good bioavailability, rifampin is now commonly administered as combination antimicrobial therapy for the treatment of various infections caused by organisms other than mycobacteria. This review summarizes the most recent clinical studies on the use of rifampin combinations for treating four common non-mycobacterial infections: acute bacterial meningitis, infective endocarditis and bacteraemia, pneumonia, and biofilm-related infections.

METHODS

We performed a literature search of clinical studies published in English from January 2005 to June 2016 using the PubMed database with the search terms "rifampin" with "meningitis" or "infective endocarditis and bacteraemia" or "pneumonia" or "prosthetic joint infections.

RESULTS

Current evidence to support a rifampin combination therapy as a treatment for non-mycobacterial infections was largely based on in vitro/in vivo studies and non-comparable retrospective case series. Additionally, controlled clinical trials that directly compared outcomes resulting from rifampin treatment versus treatment without rifampin were limited.

CONCLUSIONS

Rifampin combination therapy appears promising for the treatment of non-mycobacterial infections. However, further definitive clinical trials are necessary to validate its use because the risk of adverse drug-drug interactions and of the emergence of rifampin resistance during treatment may outweigh the potential benefits.

Antibiotic efficacy is linked to bacterial cellular respiration

Bacteriostatic and bactericidal antibiotic treatments result in two fundamentally different phenotypic outcomes--the inhibition of bacterial growth or, alternatively, cell death. Most antibiotics inhibit processes that are major consumers of cellular energy output, suggesting that antibiotic treatment may have important downstream consequences on bacterial metabolism. We hypothesized that the specific metabolic effects of bacteriostatic and bactericidal antibiotics contribute to their overall efficacy. We leveraged the opposing phenotypes of bacteriostatic and bactericidal drugs in combination to investigate their activity. Growth inhibition from bacteriostatic antibiotics was associated with suppressed cellular respiration whereas cell death from most bactericidal antibiotics was associated with accelerated respiration. In combination, suppression of cellular respiration by the bacteriostatic antibiotic was the dominant effect, blocking bactericidal killing. Global metabolic profiling of bacteriostatic antibiotic treatment revealed that accumulation of metabolites involved in specific drug target activity was linked to the buildup of energy metabolites that feed the electron transport chain. Inhibition of cellular respiration by knockout of the cytochrome oxidases was sufficient to attenuate bactericidal lethality whereas acceleration of basal respiration by genetically uncoupling ATP synthesis from electron transport resulted in potentiation of the killing effect of bactericidal antibiotics. This work identifies a link between antibiotic-induced cellular respiration and bactericidal lethality and demonstrates that bactericidal activity can be arrested by attenuated respiration and potentiated by accelerated respiration. Our data collectively show that antibiotics perturb the metabolic state of bacteria and that the metabolic state of bacteria impacts antibiotic efficacy.

Strategies and new developments in the management of bacterial meningitis

The principles of antimicrobial therapy for acute bacterial meningitis include use of agents that penetrate well into cerebrospinal fluid and attain appropriate cerebrospinal fluid concentrations, are active in purulent cerebrospinal fluid, and are bactericidal against the infecting pathogen. Recommendations for treatment of bacterial meningitis have undergone significant evolution in recent years, given the emergence of pneumococcal strains that are resistant to penicillin. Clinical experience with use of newer agents is limited to case reports, but these agents may be necessary to consider in patients who are failing standard therapy.

Emergency diagnosis and treatment of adult meningitis

Despite the existence of antibiotic therapies against acute bacterial meningitis, patients with the disease continue to suffer significant morbidity and mortality in both high and low-income countries. Dilemmas exist for emergency medicine and primary-care providers who need to accurately diagnose patients with bacterial meningitis and then rapidly administer antibiotics and adjunctive therapies for this life-threatening disease. Physical examination may not perform well enough to accurately identify patients with meningitis, and traditionally described lumbar puncture results for viral and bacterial disease cannot always predict bacterial meningitis. Results from recent studies have implications for current treatment guidelines for adults with suspected bacterial meningitis, and it is important that physicians who prescribe the initial doses of antibiotics in an emergency setting are aware of guidelines for antibiotics and adjunctive steroids. We present an overview and discussion of key diagnostic and therapeutic decisions in the emergency evaluation and treatment of adults with suspected bacterial meningitis.

Vancomycin disposition and penetration into ventricular fluid of the central nervous system following intravenous therapy in patients with cerebrospinal devices

OBJECTIVE/AIMS

To determine the cerebrospinal fluid concentrations and percent CNS penetration of intravenous vancomycin in patients with cerebrospinal devices at a pediatric institution.

METHODS

We performed a prospective evaluation of intravenous (IV) vancomycin in patients who received a single prophylactic dose of vancomycin (15-20 mg/, maximum dose 1 g) prior to insertion of a CNS shunt (group I) or a therapeutic regimen (a dose of 10-20 mg/kg every 6-12 h) for a documented/suspected shunt infection (group II). Ventricular cerebrospinal fluid (VCSF) samples were taken during the procedure in group I and multiple serum and VCSF samples were collected in group II. Pharmacokinetic parameters were calculated using a one-compartment model, and percent CNS penetration was estimated using area-under-the-curve methodology.

RESULTS

Group I: 21 VCSF samples were analyzed from 19 patients (mean age 7.2 +/- 6.4 years). Over 40% of samples failed to have detectable vancomycin concentrations (range 0-2 microg/ml). Group II: 6 patients (mean age 11 +/- 8.7 years) had VCSF concentrations ranging from nondetectable to 6.59 microg/ml (mean 2.48 +/- 0.52 microg/ml). Percent penetration ranged from 0.77 to 18%.

CONCLUSIONS

Single-dose, pre-operative vancomycin results in low VCSF vancomycin concentrations and repeated dosing in patients with documented/presumed device infections yields variable CNS penetration.

Bacterial Meningitis in Children

Acute bacterial meningitis is still an important cause of morbidity and mortality in children worldwide. Recently, Haemophilus influenzae type b (Hib), once a common cause of meningitis, has virtually disappeared in developed nations, reflecting the overwhelming success of Hib vaccination. Unfortunately, Hib remains a significant pathogen in resource-poor countries. The introduction of the conjugated pneumococcal vaccine in 2000 may lead to similar future trends as witnessed with Hib. As the resistance of Streptococcus pneumoniae to penicillin and cephalosporins continues to evolve, vancomycin has become an important antibacterial in the treatment of bacterial meningitis. The unreliable penetration of this agent into cerebrospinal fluid is of concern, which is compounded by the controversial use of corticosteroids in paediatric meningitis. Some data suggest that in certain situations the addition of rifampicin (rifampin) to ceftriaxone may be a better choice. While dexamethasone is now considered the standard adjunctive therapy in the treatment of pneumococcal meningitis in adult patients, the benefit in children is not so clear and remains controversial; thus, there is no definitive paediatric recommendation. Several anti-inflammatory agents currently under investigation may be used in the future as adjunctive therapy for bacterial meningitis. It is clear that the current concepts in the treatment of childhood bacterial meningitis are evolving, and other antibacterial options and possible alternatives such as carbapenems and fluoroquinolones should be considered. Fluid restriction because of the Syndrome of Inappropriate Antidiuretic Hormone Secretion is widely advocated and used. Yet, this practice was recently challenged. It seems that most patients with meningitis do not need fluid restriction. The overwhelming success of the conjugated Hib vaccine and the encouraging results of the new conjugated pneumococcal and meningococcal vaccines suggest that the ideal management of bacterial meningitis is prevention and vaccines development against the most common bacterial agents are the best solution.

Antimicrobial agents in the treatment of bacterial meningitis

The use of antimicrobial agents in the treatment of acute bacterial meningitis has undergone significant changes in recent years. There is a wealth of in vitro and animal model data that support the use of the specific antimicrobial agents in the treatment of bacterial meningitis, although not all regimens have been evaluated in clinical trials. Recent investigations have focused on expanding the potential antimicrobial formulary to manage patients with bacterial meningitis effectively in this era of increasing antimicrobial resistance. Despite these advances, the morbidity and mortality of acute bacterial meningitis remain unacceptably high. The use of adjunctive dexamethasone has been shown to improve morbidity and mortality in patients with bacterial meningitis, although concerns have been raised that dexamethasone may reduce penetration of certain antimicrobial agents into cerebrospinal fluid.

Acute Bacterial Meningitis in Children

Despite advances in recent decades in management, including new and effective antimicrobials, children with bacterial meningitis still incur significant morbidity and mortality. Pathophysiologic processes including colonization and migration of the bacteria to blood, seeding of the meninges, and meningeal and brain inflammation have been largely elucidated, but more specific knowledge could lead to new effective therapies. Outside of the neonatal period, the most common causative organisms have been Haemophilus influenzae, Streptococcus pneumoniae, and Neisseria meningitidis. However, conjugate vaccines, especially the H influenzae type b preparation, have contributed significantly to steep declines in the incidence of meningitis. Optimal management consists of rapid diagnosis and administration of bactericidal antibiotics with properties allowing adequate penetration of the inflamed blood-brain barrier. Recently, development of microbial resistance has resulted in changes to recommended empiric antibiotic regimens. Novel therapies are under investigation; however, until controlled trials can be conducted, these therapies cannot be recommended.

The Importance of Bactericidal Drugs: Future Directions in Infectious Disease

BACKGROUND

Although a considerable amount of research has gone into the study of the role of bactericidal versus bacteriostatic antimicrobial agents in the treatment of different infectious diseases, there is no accepted standard of practice.

METHODS

A panel of infectious diseases specialists reviewed the available literature to try to define specific recommendations for clinical practice.

RESULTS

In infections of the central nervous system, the rapidity with which the organism is killed may be an important determinant, because of the serious damage that may occur during these clinical situations. The failure of bacteriostatic antibiotics to adequately treat endocarditis is well documented, both in human studies and in animal models.

CONCLUSION

The bulk of the evidence supports the concept that, in treating endocarditis and meningitis, it is important to use antibacterial agents with in vitro bactericidal activity. This conclusion is based on both human and animal data. The data to support bactericidal drugs' superiority to bacteriostatic drugs do not exist for most other clinical situations, and animal models do not support this concept in some situations. Clinicians should be aware that drugs that are bacteriostatic for one organism may in fact be bactericidal for another organism or another strain of the same organism.

Evaluation of a triple-drug combination for treatment of experimental multidrug-resistant pneumococcal meningitis

To evaluate the therapeutic efficacy of ceftriaxone + vancomycin + rifampicin (CVR) in the treatment of pneumococcal meningitis caused by a multidrug-resistant strain, single-drug regimens (ceftriaxone 100 mg/kg, rifampicin 15 mg/kg, or vancomycin 20 mg/kg), double-drug regimens (ceftriaxone + vancomycin [CV] and ceftriaxone + rifampicin [CR]) and a triple-drug combination (CVR) with or without dexamethasone were compared in a rabbit meningitis model. Meningitis was induced by a highly penicillin-resistant (MIC 2 mg/l) and ceftriaxone-resistant (MIC 4 mg/l) pneumococcal strain. Final therapeutic efficacy was evaluated by the bacterial concentration at 24 h, and the bacterial killing rate was also evaluated. All combination regimens were superior to ceftriaxone or vancomycin single-drug regimens with regard to sterilisation of CSF and bacterial killing rate. Rifampicin was as effective as combination regimens. Regardless of dexamethasone, therapeutic efficacy of CVR and CR were superior to that of CV. CVR showed comparable therapeutic efficacy to CR. Data suggested that CVR would not have additional therapeutic benefit over CR during the initial 24 h of treatment.

Antibiotic susceptibility and serotype distribution of 240 Streptococcus pneumoniae causing meningitis in Belgium 1997-2000

Cerebrospinal fluid isolates of Streptococcus pneumoniae, collected during the years 1997-2000 at more than 100 Belgian laboratories were studied. The 10 most common serotypes-serogroups representing 76% of the isolates were 14, 6, 9, 19, 23, 18, 4, 10, 8 and 12 (in order of frequency). Thirty-six percent of strains were isolated in children < 5 years old. In this age group the number of serogroups was more limited and 81.4% are included in the 7-valent conjugate vaccine. Decreased susceptibility to penicillin was observed in 13.9% of 237 strains (MIC > 0.06 mg/L), with only 2.1% resistant strains (MIC > 1 mg/L). Twelve strains showed reduced susceptibility to cefotaxime (MIC > 0.5 mg/L). Only three of the 237 strains were intermediately susceptible to meropenem. All strains were susceptible to vancomycin and moxifloxacin. In Belgium, high doses of third generation cephalosporins remain effective for the treatment of pneumococcal meningitis. The new fluoroquinolones seem the most promising agents for the treatment of pneumococcal meningitis in the future.

Treatment of Bacterial Meningitis

The therapeutic approach to acute bacterial meningitis has changed in recent years as a result of changes in in vitro susceptibility of many meningeal pathogens to previously standard antimicrobial therapy. Given the emergence of strains of Streptococcus pneumoniae that are resistant to penicillin and the cephalosporins, the combination of vancomycin plus a third-generation cephalosporin is recommended as empiric therapy for suspected or proven pneumococcal meningitis, pending results of in vitro susceptibility testing. Strains of Neisseria meningitidis with reduced susceptibility to penicillin have also been described, although most patients with these resistant strains have recovered with standard penicillin therapy. Although the third-generation cephalosporins have greatly improved outcome in patients with meningitis caused by aerobic gram-negative bacilli, many organisms in this group are now resistant to these drugs; the carbapenems and fluoroquinolones may be effective alternative agents and have been successfully used in small case series. Further surveillance of the in vitro antimicrobial susceptibility patterns of meningeal pathogens is critical for future recommendations in the treatment of bacterial meningitis.

The antibiotic and anti-inflammatory treatment of bacterial meningitis in adults: do we have to change our strategies in an era of increasing antibiotic resistance?

Community acquired bacterial meningitis remains a feared infection because of its high morbidity and mortality. During the last decade, the incidence and the microbial resistance patterns of pathogens causing bacterial meningitis have changed considerably. A sharp increase in meningococcal disease has been observed and meningitis caused by penicillin resistant Streptococcus pneumoniae emerged as a matter of major concern. Since pneumococcal resistance in Belgium to third generation cephalosporins remains rare and low level, addition of vancomycin to the initial empirical therapy including third generation cephalosporins is not yet necessary. However, the evolution of the resistance patterns of invasive S. pneumoniae should be followed very carefully. The emergence of penicillin resistant pneumococci also raises concern about the safety of adjuvant anti-inflammatory therapy with dexamethasone. Although there is a growing evidence suggesting a decrease of neurological complications after administration of adjuvant dexamethasone, this therapy may lower the already borderline penetration through the blood-brain barrier of the currently used antibiotics. This may result in therapeutic failure. We therefore presently do not advocate the routine use of dexamethasone in the therapy of adult bacterial meningitis.