Pharmacodynamics and bactericidal activity of ceftriaxone therapy in experimental cephalosporin-resistant pneumococcal meningitis

Challenges for global antibiotic regimen planning and establishing antimicrobial resistance targets: implications for the WHO Essential Medicines List and AWaRe antibiotic book dosing

SUMMARYThe World Health Organisation's 2022 AWaRe Book provides guidance for the use of 39 antibiotics to treat 35 infections in primary healthcare and hospital facilities. We review the evidence underpinning suggested dosing regimens. Few (n = 18) population pharmacokinetic studies exist for key oral AWaRe antibiotics, largely conducted in homogenous and unrepresentative populations hindering robust estimates of drug exposures. Databases of minimum inhibitory concentration distributions are limited, especially for community pathogen-antibiotic combinations. Minimum inhibitory concentration data sources are not routinely reported and lack regional diversity and community representation. Of studies defining a pharmacodynamic target for ß-lactams (n = 80), 42 (52.5%) differed from traditionally accepted 30%-50% time above minimum inhibitory concentration targets. Heterogeneity in model systems and pharmacodynamic endpoints is common, and models generally use intravenous ß-lactams. One-size-fits-all pharmacodynamic targets are used for regimen planning despite complexity in drug-pathogen-disease combinations. We present solutions to enable the development of global evidence-based antibiotic dosing guidance that provides adequate treatment in the context of the increasing prevalence of antimicrobial resistance and, moreover, minimizes the emergence of resistance.

The Blood-Brain Barrier and Pharmacokinetic/Pharmacodynamic Optimization of Antibiotics for the Treatment of Central Nervous System Infections in Adults

Bacterial central nervous system (CNS) infections are serious and carry significant morbidity and mortality. They encompass many syndromes, the most common being meningitis, which may occur spontaneously or as a consequence of neurosurgical procedures. Many classes of antimicrobials are in clinical use for therapy of CNS infections, some with established roles and indications, others with experimental reporting based on case studies or small series. This review delves into the specifics of the commonly utilized antibacterial agents, updating their therapeutic use in CNS infections from the pharmacokinetic and pharmacodynamic perspectives, with a focus on the optimization of dosing and route of administration that have been described to achieve good clinical outcomes. We also provide a concise synopsis regarding the most focused, clinically relevant information as pertains to each class and subclass of antimicrobial therapeutics. CNS infection morbidity and mortality remain high, and aggressive management is critical in ensuring favorable patient outcomes while averting toxicity and upholding patient safety.

Central nervous system infections and antimicrobial resistance: an evolving challenge

PURPOSE OF REVIEW

Antimicrobial resistance is an increasing threat to patients also in nosocomial central nervous system (CNS) infections. The present review focusses on optimizing intravenous treatment in order to achieve sufficient concentrations of antibiotics in the different compartments of the CNS when the causative pathogens have reduced sensitivity to antibiotics or/and the impairment of the blood-cerebrospinal fluid (CSF) and blood-brain barrier is mild.

RECENT FINDINGS

Experience has been gathered with treatment protocols for several established antibiotics using increased doses or continuous instead of intermittent intravenous therapy. Continuous infusion in general does not increase the average CSF concentrations (or the area under the concentration-time curve in CSF) compared to equal daily doses administered by short-term infusion. In some cases, it is postulated that it can reduce toxicity caused by high peak plasma concentrations. In case reports, new β-lactam/β-lactamase inhibitor combinations were shown to be effective treatments of CNS infections.

SUMMARY

Several antibiotics with a low to moderate toxicity (in particular, β-lactam antibiotics, fosfomycin, trimethoprim-sulfamethoxazole, rifampicin, vancomycin) can be administered at increased doses compared to traditional dosing with low or tolerable adverse effects. Intrathecal administration of antibiotics is only indicated, when multiresistant pathogens cannot be eliminated by systemic therapy. Intravenous should always accompany intrathecal treatment.

Pharmacokinetics/Pharmacodynamics models of veterinary antimicrobial agents

Misuse and abuse of veterinary antimicrobial agents have led to an alarming increase in bacterial resistance, clinical treatment failure, and drug residues. To address these problems, consistent and appropriate dosage regimens for veterinary antimicrobial agents are needed. Pharmacokinetics/Pharmacodynamics (PK/PD) models have been widely used to establish rational dosage regimens for veterinary antimicrobial agents that can achieve effective prevention and treatment of bacterial diseases and avoid the development of bacterial resistance. This review introduces building methods for PK/PD models and describes current PK/PD research progress toward rational dosage regimens for veterinary antimicrobial agents. Finally, the challenges and prospects of PK/PD models in the design of dosage regimens for veterinary antimicrobial agents are reviewed. This review will help to increase awareness of PK/PD modeling among veterinarians and hopefully promote its development and future use.

Receptor Blockade: A Novel Approach to Protect the Brain From Pneumococcal Invasion

Background

Pneumococci are the major cause of bacterial meningitis globally. To cause meningitis pneumococci interact with the 2 endothelial receptors, polymeric immunoglobulin receptor (pIgR) and platelet endothelial cell adhesion molecule (PECAM-1), to penetrate the blood-brain barrier (BBB) and invade the brain.

Methods

C57BL/6 mice were infected intravenously with bioluminescent pneumococci, and treated with ceftriaxone (1 hour postinfection) and anti-pIgR and PECAM-1 antibodies (1 or 5 hours postinfection), then monitored for 5 and 10 days. Bacterial brain invasion was analyzed using IVIS imaging and bacterial counts.

Results

Ceftriaxone, given early after pneumococcal challenge, cleared pneumococci from the blood but not from the brain. After combining ceftriaxone with receptor blockade, using anti-pIgR and PECAM-1 antibodies, we found 100% survival after 5 and 10 days of infection, in contrast to 60% for ceftriaxone alone. Combined antibiotic and antibody treatment resulted in no or few viable bacteria in the brain and no microglia activation. Antibodies remained bound to the receptors during the study period. Receptor blockade did not interfere with antibiotic permeability through the BBB.

Conclusions

We suggest that adjunct treatment with pIgR and PECAM-1 antibodies to antibiotics may prevent pneumococcal meningitis development and associated brain damages. However, further evaluations are required.

Antibiotic Distribution into Cerebrospinal Fluid: Can Dosing Safely Account for Drug and Disease Factors in the Treatment of Ventriculostomy-Associated Infections?

Ventriculostomy-associated infections, or ventriculitis, in critically ill patients are associated with considerable morbidity. Efficacious antibiotic dosing for the treatment of these infections may be complicated by altered antibiotic concentrations in the cerebrospinal fluid due to variable meningeal inflammation and antibiotic properties. Therefore, doses used to treat infections with a higher degree of meningeal inflammation (such as meningitis) may often fail to achieve equivalent exposures in patients with ventriculostomy-associated infections such as ventriculitis. This paper aims to review the disease burden, infection rates, and common pathogens associated with ventriculostomy-associated infections. This review also seeks to describe the disease- and drug-related factors that influence antibiotic distribution into cerebrospinal fluid and provide a critical appraisal of current dosing of antibiotics commonly used to treat these types of infections. A Medline search of relevant articles was conducted and used to support a review of cerebrospinal fluid penetration of vancomycin, including critical appraisal of the recent paper by Beach et al. recently published in this journal. We found that in the intensive care unit, ventriculostomy-associated infections are the most common and serious complication of external ventricular drain insertion and often result in prolonged patient stay and increased healthcare costs. Reported infection rates are extremely variable (between 0 and 45%), hindered by the inherent diagnostic difficulty. Both Gram-positive and Gram-negative organisms are associated with such infections and the rise of multi-drug-resistant pathogens means that effective treatment is an ongoing challenge. Disease factors that may need to be considered are reduced meningeal inflammation and the presence of critical illness; drug factors include physiochemical properties, degree of plasma-protein binding, and affinity to active transporter proteins present in the blood-cerebrospinal fluid barrier. The relationship between cerebrospinal fluid antibiotic exposures in the setting of ventriculostomy-associated infection and clinical response has not been fully elucidated for many of the antibiotics commonly used in its treatment. More thorough and clinically relevant investigations are needed to better define blood pharmacokinetic/pharmacodynamics targets and optimal therapeutic exposures for treatment of ventriculostomy-associated infections. It is hoped that this future research will be able to provide clearer recommendations for clinicians frequently faced with dosing-related dilemmas when treating patients with these challenging infections.

Genetic and pharmacological manipulation of glial glutamate transporters does not alter infection-induced seizure activity

The contribution of glial transporters to glutamate movement across the membrane has been identified as a potential target for anti-seizure therapies. Two such glutamate transporters, GLT-1 and system x_c^-, are expressed on glial cells, and modulation of their expression and function have been identified as a means by which seizures, neuronal injury, and gliosis can be reduced in models of brain injury. While GLT-1 is responsible for the majority of glutamate uptake in the brain, system x_c^- releases glutamate in the extracellular cleft in exchange for cystine and represents as such the major source of hippocampal extracellular glutamate. Using the Theiler's Murine Encephalomyelitis Virus (TMEV) model of viral-induced epilepsy, we have taken two well-studied approaches, one pharmacological, one genetic, to investigate the potential role(s) of GLT-1 and system x_c^- in TMEV-induced pathology. Our findings suggest that the methods we utilized to modulate these glial transporters, while effective in other models, are not sufficient to reduce the number or severity of behavioral seizures in TMEV-infected mice. However, genetic knockout of xCT, the specific subunit of system x_c^-, may have cellular effects, as we observed a slight decrease in neuronal injury caused by TMEV and an increase in astrogliosis in the CA1 region of the hippocampus. Furthermore, xCT knockout caused an increase in GLT-1 expression selectively in the cortex. These findings have significant implications for both the characterization of the TMEV model as well as for future efforts to discover novel and effective anti-seizure drugs.

Cerebrospinal fluid penetration of very high-dose meropenem: a case report

Background

Standard dosing of meropenem (2 g t.i.d.) produces CSF concentrations of only 1–2 mg/L which is inferior to the clinical breakpoint for most Gram-negative bacteria. There is therefore concern that dosing must be increased in order to achieve therapeutic CSF concentrations for bacteria with susceptibility close to clinical breakpoints. Yet, the effects of high-dose meropenem on CSF concentrations are not well described in literature. We therefore determined meropenem CSF-levels in a patient who was treated with 15 g/day of meropenem.

Case presentation

Our patient suffered from a brain trauma and an external ventricular drainage was implanted. Later, a carbapenemase-producing Acinetobacter baumannii (OXA-23, NDM-1) was isolated from blood cultures and CSF. The MIC for meropenem was > 32 mg/L (R), and we opted for a combination therapy of meropenem, colistin and fosfomycin. Meropenem was given at an unusual high-dose (15 g/day) with the aim of achieving high CSF concentrations. CSF concentrations peaked at 64 mg/L. Yet, the patient succumbed to an intracranial bleed into a preexisting cerebral contusion.

Conclusions

High-dose meropenem can achieve CSF levels largely superior to those achieved with commonly recommended dosing regimens. Though our patient succumbed to an intracranial bleed which could be regarded as a severe adverse event, we suggest that meropenem dosing can be increased when pathogens with increased MICs are found in the CSF. More in vivo data are however needed to determine the safety of high-dose meropenem.

Evaluation of the Synergistic Effect of Tomatidine with Several Antibiotics against Standard and Clinical Isolates of Staphylococcus aureus, Enterococcus faecalis, Pseudomonas aeruginosa and Escherichia coli

Antibiotic resistance is an important problem in antibiotic treatment of infections, particularly in hospitals. Tomatidine is a plant secondary metabolite with antimicrobial and antifungal effects. This study examined the possible synergistic effect tomatidine with several antibiotics against standard and clinical strains of Staphylococcus aureus, Enterococcus faecalis, Pseudomonas aeruginosa and Escherichia coli. After determining the minimum inhibitory concentrations (MICs) of antibiotics and tomatidine against the bacterial isolates using broth microdilution method, the synergistic effect between tomatidine and antibiotics was evaluated by checkerboard method and calculation of FIC indices. Tomatidine alone did not show any antimicrobial effect. However, it had synergistic effect with gentamicin and cefepime against standard and clinical isolates of S. aureus and P. aeruginosa, respectively. It also had synergistic effect with ampicillin and ciprofloxacin only against standard strains of E. faecalis and P. aeruginosa, respectively. In conclusion, tomatidine could be considered as a potential antibiotic potentiator for gentamicin, cefepime and ciprofloxacin, and ampicillin against Staphylococcus aureus, Pseudomonas aeruginosa, and Enterococcus faecalis infections, respectively. However, the toxicological and pharmacological properties of tomatidine for use as a therapeutic agent remain to be determined.

The UK joint specialist societies guideline on the diagnosis and management of acute meningitis and meningococcal sepsis in immunocompetent adults

Bacterial meningitis and meningococcal sepsis are rare conditions with high case fatality rates. Early recognition and prompt treatment saves lives. In 1999 the British Infection Society produced a consensus statement for the management of immunocompetent adults with meningitis and meningococcal sepsis. Since 1999 there have been many changes. We therefore set out to produce revised guidelines which provide a standardised evidence-based approach to the management of acute community acquired meningitis and meningococcal sepsis in adults. A working party consisting of infectious diseases physicians, neurologists, acute physicians, intensivists, microbiologists, public health experts and patient group representatives was formed. Key questions were identified and the literature reviewed. All recommendations were graded and agreed upon by the working party. The guidelines, which for the first time include viral meningitis, are written in accordance with the AGREE 2 tool and recommendations graded according to the GRADE system. Main changes from the original statement include the indications for pre-hospital antibiotics, timing of the lumbar puncture and the indications for neuroimaging. The list of investigations has been updated and more emphasis is placed on molecular diagnosis. Approaches to both antibiotic and steroid therapy have been revised. Several recommendations have been given regarding the follow-up of patients.

A pharmacokinetic/pharmacodynamic analysis of ceftaroline prophylaxis in patients with external ventricular drains

BACKGROUND

Ceftaroline is a broad-spectrum cephalosporin antibiotic with activity against drug-resistant bacteria, including strains of methicillin-resistant Staphylococcus aureus (MRSA), and may be useful to prevent and treat ventriculostomy-related infections (VRIs). The purpose of this study was to analyze the pharmacokinetics and pharmacodynamics of prophylactic ceftaroline in neurosurgical patients with an external ventricular drain (EVD).

METHODS

Adult patients in the neurosurgical intensive care unit with an EVD were given prolonged prophylaxis with ceftaroline. Serum and cerebral spinal fluid (CSF) were obtained simultaneously at 2, 6, and 12 h after initiation of the fourth dose of ceftaroline and concentrations were measured by a liquid chromatography tandem mass spectrometry assay. Time-kill curves against isolates of coagulase-negative S. aureus, methicillin-sensitive S. aureus, MRSA, and Streptococcus pneumoniae were determined in serum and CSF at each collection time point.

RESULTS

A total of five patients with a mean age of 63 y and mean weight of 83 kg were enrolled. The mean CSF:serum penetration ratios of ceftaroline were 0.005 (0.5%), 0.021 (2.1%), and 0.043 (4.3%) at 2, 6, and 12 h, respectively. The mean ceftaroline exposure ratio area under the curve (AUC)csf/AUCserum) was 0.011 (1.1%). Bactericidal activity at each collection time point was observed against each strain of staphylococci from serum samples and a penicillin-sensitive strain of S. pneumoniae from CSF samples.

CONCLUSION

This investigation suggests that ceftaroline could have clinical utility for the prevention of VRIs in patients with EVDs.

Clinical pharmacokinetics of antibacterials in cerebrospinal fluid

In the past 20 years, an increased discrepancy between new available antibacterials and the emergence of multidrug-resistant strains has been observed. This condition concerns physicians involved in the treatment of central nervous system (CNS) infections, for which clinical and microbiological success depends on the rapid achievement of bactericidal concentrations. In order to accomplish this aim, the choice of drugs is based on their disposition toward the cerebrospinal fluid (CSF), which is influenced by the physicochemical characteristics of antibacterials. A reduced distribution into CSF has been documented for beta-lactams, especially cephalosporins and carbapenems, on the basis of their hydrophilic nature. However, they represent a cornerstone of the majority of combined therapeutic schemes for their ability to achieve bactericidal concentrations, especially in the presence of inflamed meninges. The good tolerability of beta-lactams makes possible high daily dose intensities, which may be associated with increased probability of cure. Furthermore, the adoption of continuous infusion seems to be a fruitful option. Fluoroquinolones, namely moxifloxacin, and antituberculosis drugs, together with the agents such as linezolid, reach the highest CSF/plasma concentration ratio, which is greater than 0.8, and for most of these drugs it is near 1. For all drugs that are currently used for the treatment of CNS infections, the evaluation of pharmacokinetic/pharmacodynamic parameters, on the basis of dosing regimens and their time-dependent or concentration-dependent pattern of bacterial killing, remains an important aspect of clinical investigation and medical practice.

Pharmacokinetic-pharmacodynamic modeling of antibacterial drugs

Pharmacokinetic-pharmacodynamic (PKPD) modeling and simulation has evolved as an important tool for rational drug development and drug use, where developed models characterize both the typical trends in the data and quantify the variability in relationships between dose, concentration, and desired effects and side effects. In parallel, rapid emergence of antibiotic-resistant bacteria imposes new challenges on modern health care. Models that can characterize bacterial growth, bacterial killing by antibiotics and immune system, and selection of resistance can provide valuable information on the interactions between antibiotics, bacteria, and host. Simulations from developed models allow for outcome predictions of untested scenarios, improved study designs, and optimized dosing regimens. Today, much quantitative information on antibiotic PKPD is thrown away by summarizing data into variables with limited possibilities for extrapolation to different dosing regimens and study populations. In vitro studies allow for flexible study designs and valuable information on time courses of antibiotic drug action. Such experiments have formed the basis for development of a variety of PKPD models that primarily differ in how antibiotic drug exposure induces amplification of resistant bacteria. The models have shown promise for efficacy predictions in patients, but few PKPD models describe time courses of antibiotic drug effects in animals and patients. We promote more extensive use of modeling and simulation to speed up development of new antibiotics and promising antibiotic drug combinations. This review summarizes the value of PKPD modeling and provides an overview of the characteristics of available PKPD models of antibiotics based on in vitro, animal, and patient data.

Treatment of Drug-resistant Pneumococcal Meningitis

The approach to therapy in patients with pneumococcal meningitis has changed considerably over the past 20 years. Given the emergence of pneumococcal strains that are intermediately susceptible or highly resistant to penicillin, penicillin is not recommended as empiric therapy for presumed pneumococcal meningitis; the combination of vancomycin and a third-generation cephalosporin (either cefotaxime or ceftriaxone) should be used, pending isolation of the organism and in vitro susceptibility testing. For patients with pneumococcal meningitis caused by highly penicillin- or cephalosporin-resistant strains, the addition of rifampin can be considered if the organism is susceptible in vitro, the expected clinical or bacteriologic response is delayed, or the pneumococcal isolate has a cefotaxime or ceftriaxone minimal inhibitory concentration greater than 4 μg/mL. Meropenem is not a good option for monotherapy of highly penicillin- or cephalosporin-resistant strains, but use of a fluoroquinolone with in vitro activity against Streptococcus pneumoniae (specifically moxifloxacin) is an option in patients failing standard therapy; if used, however, it should be combined with a third-generation cephalosporin or vancomycin. Newer glycopeptides, daptomycin, and linezolid require further study to determine their efficacy in patients with pneumococcal meningitis.

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.

Principles of antimicrobial therapy

We have discussed important factors involved in choosing appropriate antimicrobial regimens for the treatment of bacterial meningitis and brain abscess to illustrate common themes relevant to the treatment of these diseases. We have limited this review to these conditions for two main reasons: (1) the principles involved in optimal antimicrobial therapy for these diseases likely apply to others CNS infections, such as viral and fungal diseases; and (2) little pharmacological information is currently available for other types of CNS infections. Many of the studies addressing the relevant pharmacological and microbiological aspects of antimicrobial therapy for CNS infections have been performed in experimental animal models and, as a result, the information derived from these studies may be different when examined in appropriate human studies. Our current understanding of appropriate antimicrobial therapy for CNS infections may be summarized as follows: 1. Choose bactericidal antimicrobials that effectively cross the BBB to achieve CSF concentrations well above the MBC (≥ 10-fold) for the suspected bacterial pathogen(s). 2. Take into consideration the relevant PD parameters the bactericidal activity of the antimicrobials used to treat bacterial meningitis, such as t > MBC or AUC/MBC. 3. Tailor the antimicrobial regimen based on microbiological information, once available. However, with respect to brain abscess therapy, keep in mind that anaerobes are commonly involved, but difficult to culture, and consider including antianaerobic therapy even if the bacterial cultures do not grow anaerobes. 4. Treat bacterial meningitis caused by nonmeningococcal pathogens for 7-10 days, but monitor clinical progress to determine whether the patient should continue on a more prolonged antimicrobial course. Meningococcal meningitis may be treated with 3-4 days of effective antimicrobial therapy, again with the caveat that the patients clinical course should dictate duration of therapy. 5. Treat brain abscess, preferably after aspiration/drainage, for at least 6 weeks with intravenous antimicrobials for brain abscess on the clinical response (e.g., improved symptoms, lack of new neurological findings) and radiographic changes (e.g., reduction in cavity size).

[Presumptive bacterial meningitis in adults: initial antimicrobial therapy]

CSF sterilization should be obtained very rapidly to reduce both mortality and morbidity due to bacterial meningitis. Thus, antibiotic treatment should be adapted to the suspected bacterium and administered as early as possible at high dosage with - if necessary - a loading dose and continuous perfusion. The rates of abnormal susceptibility to penicillin of Streptococcus pneumoniae, Neisseria meningitis and Haemophilus influenzae are 37%, 30% and 12% respectively. Thus, ceftriaxone or cefotaxim must be used as empirical treatment. Listeria monocytogenes remains fully susceptible to aminopenicillin, so, the combination aminopenicillin and aminoglycoside is the first-line treatment. Antibiotic resistance, allergy or contra-indications, are in fact rare but in these cases, antibiotic combinations are often needed. The latter are more or less complex and clinically validated; they include molecules such as vancomycine, fosfomycin, fluoroquinolone or linezolid.

Management of meningitis due to antibiotic-resistant Acinetobacter species

Acinetobacter meningitis is becoming an increasingly common clinical entity, especially in the postneurosurgical setting, with mortality from this infection exceeding 15%. Infectious Diseases Society of America guidelines for therapy of postneurosurgical meningitis recommend either ceftazidime or cefepime as empirical coverage against Gram-negative pathogens. However, assessment of the pharmacodynamics of these cephalosporins in cerebrospinal fluid suggests that recommended doses will achieve pharmacodynamic targets against fewer than 10% of contemporary acinetobacter isolates. Thus, these antibiotics are poor options for suspected acinetobacter meningitis. From in vitro and pharmacodynamic perspectives, intravenous meropenem plus intraventricular administration of an aminoglycoside may represent a superior, albeit imperfect, regimen for suspected acinetobacter meningitis. For cases of meningitis due to carbapenem-resistant acinetobacter, use of tigecycline is not recommended on pharmacodynamic grounds. The greatest clinical experience rests with use of polymyxins, although an intravenous polymyxin alone is inadvisable. Combination with an intraventricularly administered antibiotic plus removal of infected neurosurgical hardware appears the therapeutic strategy most likely to succeed in this situation. Unfortunately, limited development of new antibiotics plus the growing threat of multidrug-resistant acinetobacter is likely to increase the problems posed by acinetobacter meningitis in the future.

Pharmacokinetic parameters of ceftriaxone after single intravenous and intramuscular administration in camels (Camelus Dromedarius)

The purpose of this study was to investigate the plasma disposition kinetics of ceftriaxone in female camels (n=5) following a single intravenous (i.v.) bolus or intramuscular (i.m.) injections at a dosage of 10mg kg(-1) body weight in all animals. A crossover design was carried out in two phases separated by 15 days. Jugular blood samples were collected serially for 48h and the plasma was analysed by high-performance liquid chromatography (HPLC). Following single i.v. injections the plasma concentration time curves of ceftriaxone were best fitted to a two-compartment model. The drug was rapidly distributed with half-life of distribution t(1/2alpha) of 0.24+/-0.01h and moderately eliminated with elimination rate constant and elimination half-life of 0.27+/-0.13h(-1) and 2.57+/-0.52h, respectively. The volume of distribution at steady state (V(dss)) was 0.32+/-0.01lkg(-1) and the total body clearance (Cl(tot)) was 0.11+/-0.01lkg(-1)h(-1), respectively. Following i.m. administration, the mean T(max), C(max), t(1/2el) and AUC values for plasma data were 1.03+/-0.23h, 21.54+/-2.61microg ml(-1), 1.76+/-0.03h and 85.82+/-11.21microg ml(-1)h(-1), respectively. The i.m. bioavailability was 93.42+/-21.4% and the binding percentage of ceftriaxone to plasma protein was moderate, ranging from 33% to 42% with an average of 34.5%.

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.

Pharmacodynamic profiling of cefepime in plasma and cerebrospinal fluid of hospitalized patients with external ventriculostomies

Population pharmacokinetic (PK) modeling and Monte Carlo simulation (MCS) were used to describe the pharmacodynamic profile of cefepime in the both plasma and cerebrospinal fluid (CSF). Plasma and CSF cefepime data were obtained from a PK study of 7 hospitalized patients with external ventricular drains. Concentration-time profiles in plasma and CSF were modeled using a 3-compartment model with zero-order infusion and first-order elimination and transfer. Estimates of the PK parameters were identified in the Big Non Parametric Adaptive Grid with adaptive gamma (BigNPAG) program of Leary, Jelliffe, Schumitzky, and Van Guilder. MCS (10,000 subjects) was performed to estimate the probability of attaining the targets of free plasma concentration (20% protein binding) and total drug CSF concentration of 50-100% T>minimal inhibitory concentration (MIC) for MICs 0.06-8 mg/L for cefepime 2 g, iv, every 8 h (0.5-h infusion); cefepime 2 g, iv, every 12 h (0.5-h infusion); and cefepime 2 g (0.5-h infusion) once and 250 mg/h continuous infusion. After the Bayesian step, the observed-predicted regression and r(2) for plasma and CNS were as follows: plasma, observed=0.984 x predicted+2.570, r(2)=0.944; CSF, observed=0.785 x predicted+0.868, r(2)=0.821. The median penetration of cefepime as measured by AUC(CSF)/AUC(plasma) was 7.8%. In the MCS, the target attainment rates in plasma for 60-70% fT>MIC were high at each MIC value between 0.03 and 8 microg/mL for each regimen examined. In CSF, none of the regimens achieved 50-100% T>MIC for>80% of patients for MICs>0.5 mg/L.

Bactericidal activities of parenteral antibiotics and genotype of penicillin-binding protein in Streptococcus pneumoniae and Haemophilus influenzae isolated from children's blood

A total of 16 isolates of Streptococcus pneumoniae and 18 isolates of Haemophilus influenzae were obtained from the blood of children admitted to the pediatric wards of hospitals in Hokkaido Kamikawa subprefecture between January 2003 and December 2005. The ages of the patients with S. pneumoniae or H. influenzae infection ranged from 2 months to 9 years and from 1 month to 4 years, respectively. The diagnoses of S. pneumoniae infection were as follows: pneumonia in 8 patients, occult bacteremia in 5 patients, and meningitis in 3 patients. The diagnoses of H. influenzae were: meningitis in 6 patients, pneumonia in 4 patients, occult bacteremia in 4 patients, epiglotitis in 2 patients, and facial cellulitis in 2 patients. Out of 16 S. pneumoniae isolates, penicillin-resistant strains with a mutation of 3 genes were observed in 7 children, and penicillin intermediate-resistant strains with a mutation of 1 or 2 genes were observed in 8 children. Out of 18 H. influenzae isolates, the beta-lactamase-negative ampicillin-resistant strain with a substitution of 2 points in the ftsI gene was revealed in 2 children, the beta-lactamase-negative ampicillin-resistant strain with a substitution of 1 point in the ftsI gene was observed in 4 children, the beta-lactamase-positive amoxicillin/clavulanic acid-resistant strain with blaTEM-1 and ftsI with 2 substitutions in the ftsI gene was observed in 3 children, and the beta-lactamase-positive ampicillin-resistant strain with blaTEM-1was not observed. The MBC90s of ampicillin, ceftriaxone, cefotaxime, meropenem, panipenem, and vancomycin against S. pneumoniae were 8 microg/ml, 1 microg/ml, 1 microg/ml 1 microg/ml, 0.25 microg/ml, and 0.5 microg/ml, respectively. Those of ampicillin, piperacillin, ceftriaxone, cefotaxime, meropenem, and panipenem against H. influenzae were >128 microg/ml, >128 microg/ml, 0.25 microg/mL, 1 microg/ml, 0.12 microg/ml, and 0.5 g/ml, respectively. It is suggest that the minimum bactricidal concentration (MBC) was dissociated from the minimum inhibitory concentration (MIC) in S. pneumoniae and H. influenzae with abnormal pbp genes.

Relationship between pharmacokinetics and pharmacodynamics of beta-lactams and outcome

The in-vitro susceptibility of an organism and the pharmacokinetics of an antimicrobial agent are two basic factors on which the choice of standardised treatment regimens is based. However, the inter-individual variability of these factors, which modifies the exposure of bacteria to an antibiotic in terms of time and quantity, is not usually taken into account. In 87 patients treated with beta-lactams (ceftriaxone, cefepime or piperacillin), the probability of failure was greater when the infectious process was located in tissues with barriers to the distribution of beta-lactams. Mean MICs of piperacillin and cefepime, but not ceftriaxone, were below the breakpoints in cases of both recovery and failure, but organisms isolated from patients with a poor outcome had higher MICs. Therefore, the use of breakpoints to determine the susceptibility of microorganisms was not satisfactory in predicting the outcome for a large number of patients. If MICs are determined and plasma concentrations are monitored, dosages can be adjusted according to these parameters, thereby allowing antibiotic treatment to be individualised.

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.

Meropenem Administered as a Prolonged Infusion to Treat Serious Gram-Negative Central Nervous System Infections

The treatment of gram-negative infection of the central nervous system (CNS) presents a clinical challenge due to antibiotic resistance and difficulties with penetration into the cerebrospinal fluid (CSF). Two patients with gram-negative CNS infections were treated successfully with high-dose, prolonged infusions of meropenem. The CSF meropenem concentrations exceeded the minimum inhibitory concentration of the pathogen for virtually the entire dosing interval in both cases. Our experience demonstrates that dosage modification to maximize pharmacodynamic targets and bactericidal activity may be practically applied to optimize antibiotic treatment for difficult-to-treat CNS infections.

Pharmacokinetic and pharmacodynamic issues in the treatment of bacterial infectious diseases

This review outlines some of the many factors a clinician must consider when selecting an antimicrobial dosing regimen for the treatment of infection. Integration of the principles of antimicrobial pharmacology and the pharmacokinetic parameters of an individual patient provides the most comprehensive assessment of the interactions between pathogen, host, and antibiotic. For each class of agent, appreciation of the different approaches to maximize microbial killing will allow for optimal clinical efficacy and reduction in risk of development of resistance while avoiding excessive exposure and minimizing risk of toxicity. Disease states with special considerations for antimicrobial use are reviewed, as are situations in which pathophysiologic changes may alter the pharmacokinetic handling of antimicrobial agents.

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.

Daily variations in ceftriaxone pharmacokinetics in rats

The aim of this study was to determine whether the time of day ceftriaxone was administered modified its pharmacokinetics. Ceftriaxone was given intraperitoneally at either 0400, 1000, 1600, and 2200 h to Sprague-Dawley rats synchronized under a light-dark cycle of 12 h of light and 12 h of dark. Pharmacokinetic parameters were analyzed for the presence of a 24-h rhythm. Results showed significant daily variations (P < 0.05) in ceftriaxone clearance, with the highest values during the dark phase. It is concluded that time-dependent variations in ceftriaxone pharmacokinetics may affect the therapeutic efficacy of current once-daily dosing schedules.

Garenoxacin (BMS-284756) and moxifloxacin in experimental meningitis caused by vancomycin-tolerant pneumococci

The emergence of multidrug-resistant strains of Streptococcus pneumoniae drives the development and evaluation of new antipneumococcal agents, especially for the treatment of bacterial meningitis. The aims of the present study were to assess the antibacterial effectiveness of two new quinolones, garenoxacin (BMS; BMS-284756) and moxifloxacin (MOX) in experimental meningitis caused by a vancomycin (VAN)-tolerant S. pneumoniae strain and to compare the results with those obtained by therapy with VAN and ceftriaxone (CRO) in combination. Meningitis was induced in young male New Zealand White rabbits by intracisternal inoculation of a VAN-tolerant pneumococcal strain (strain Tupelo) from a child with meningitis. Sixteen hours after inoculation, therapy was given by intravenous administration of BMS at 20 mg/kg of body weight, followed 5 h later by administration at a dosage of 10 mg/kg (n = 9 animals) or MOX as two doses of 20 mg/kg every 5 h (n = 8 animals). For comparison, we studied the following groups: (i) animals treated with VAN (20 mg/kg every 5 h, three doses) and CRO (125 mg/kg, one dose) (n = 9), (ii) animals infected with a VAN-tolerant strain but not treated (n = 8), (iii) animals infected with a VAN-tolerant pneumococcus isolated from the nasopharynx of a carrier and treated with BMS (n = 8), and (iv) animals infected with a cephalosporin-resistant type 6B S. pneumoniae strain and treated with BMS (n = 6). The MICs of penicillin, CRO, VAN, BMS, and MOX for the Tupelo strain were 2, 1, 0.5, 0.06, and 0.03 micro g/ml, respectively. The rates of killing of strain Tupelo (the change in the log(10) number of CFU per milliliter per hour) in cerebrospinal fluid at 5 h were -0.70 +/- 0.35, -0.61 +/- 0.44, and -0.49 +/- 0.36 for BMS, MOX, and VAN-CRO, respectively. Therapy with BMS and MOX was as effective as therapy with VAN-CRO against VAN-tolerant pneumococcal meningitis in rabbits.

Ceftriaxone: an update of its use in the management of community-acquired and nosocomial infections

Ceftriaxone is a parenteral third-generation cephalosporin with a long elimination half-life which permits once-daily administration. It has good activity against Streptococcus pneumoniae, methicillin-susceptible staphylococci, Haemophilus influenzae, Moraxella catarrhalis and Neisseria spp. Although active against Enterobacteriaceae, the recent spread of derepressed mutants which hyperproduce chromosomal beta-lactamases and extended-spectrum beta-lactamases has diminished the activity of all third-generation cephalosporins against these pathogens necessitating careful attention to sensitivity studies. Extensive data from randomised clinical trials confirm the efficacy of ceftriaxone in serious and difficult-to-treat community-acquired infections including meningitis, pneumonia and nonresponsive acute otitis media. Ceftriaxone also has efficacy in other community-acquired infections including uncomplicated gonorrhoea, acute pyelonephritis and various infections in children. In the nosocomial setting, extensive data also confirm the efficacy of ceftriaxone with or without an aminoglycoside in serious Gram-negative infections, pneumonia, spontaneous bacterial peritonitis and as surgical prophylaxis. Outpatient use of ceftriaxone, either as part of a step-down regimen or parenterally, is a distinguishing feature of the data gathered on the agent over the last decade. The review focuses on new applications of the drug and its use in infections in which the causative pathogens or their resistance patterns have changed over the past decade. Ceftriaxone has a good tolerability profile, the most common events being diarrhoea, nausea, vomiting, candidiasis and rash. Ceftriaxone may cause reversible biliary pseudolithiasis, notably at higher dosages of the drug (>/=2 g/day); however, the incidence of true lithiasis is <0.1%. Injection site discomfort or phlebitis can occur after intramuscular or intravenous administration.

CONCLUSIONS

As a result of its strong activity against S. pneumoniae, ceftriaxone holds an important place, either alone or as part of a combination regimen, in the treatment of invasive pneumococcal infections, including those with reduced beta-lactam susceptibility. Its once-daily administration schedule allows simplification of otherwise complex regimens in a hospital setting and has also contributed to its popularity as a parenteral agent in an ambulatory setting. These properties, together with a well characterised tolerability profile, mean that ceftriaxone is likely to retain its place as an important third-generation cephalosporin in the treatment of serious community-acquired and nosocomial infections.

Pharmacokinetics of ceftriaxone administered by the intravenous, intramuscular or subcutaneous routes to dogs

The purpose of this study was to investigate the pharmacokinetics of ceftriaxone after single intravenous (i.v.), intramuscular (i.m.) and subcutaneous (s.c.) doses in healthy dogs. Six mongrel dogs received ceftriaxone (50 mg/kg) by each route in a three-way crossover design. Blood samples were collected in predetermined times after drug administration. Results are reported as mean +/- standard deviation (SD). Total body clearance (Cl(t)) and apparent volume of distribution (V(z)) for the i.v. route were 3.61 +/- 0.78 and 0.217 +/- 0.03 mL/kg, respectively. Terminal half-life harmonic mean (t(1/2 lambda)) was 0.88; 1.17 and 01.73 h for the i.v., i.m and s.c. routes, respectively. Mean peak serum concentration (C(max)) was 115.10 +/- 16.96 and 69.28 +/- 14.55 microg/mL for the i.m and s.c. routes, respectively. Time to reach C(max) (t(max)) was 0.54 +/- 0.24 and 1.29 +/- 00.64 h for the i.m and s.c. routes, respectively. Mean absorption time (MAT) was 1.02 +/- 0.64 and 2.23 +/- 00.73 h for the i.m and s.c. routes, respectively. Bioavailability was 102 +/- 27 and 106 +/- 14% for the i.m and s.c. routes, respectively. Statistically significant differences were determined in C(max), t(max), MAT and t(1/2 lambda) of s.c. administered ceftriaxone when compared with the i.v and i.m. routes. These findings suggest that once or twice s.c. or i.m. daily administered ceftriaxone should be adequate to treat most susceptible infections in dogs.

What do we really know about antibiotic pharmacodynamics?

Antibiotic pharmacodynamics is an evolving science that focuses on the relationship between drug concentration and pharmacologic effect, which is an antibiotic-induced bacterial death that also can manifest as an adverse drug reaction. The pharmacologic action of antibiotics usually can be described as concentration dependent or independent, although such classifications are highly reliant on the specific antibiotic and bacterial pathogen being studied. Quantitative pharmacodynamic parameters, such as ratio of the area under the concentration-time curve during a 24-hour dosing period to minimum inhibitory concentration (AUC0-24:MIC), ratio of maximum serum antibiotic concentration to MIC (Cmax:MIC), and duration of time that antibiotic concentrations exceed MIC (T>MIC), have been proposed as likely predictors of clinical and microbiologic success or failure for different pairings of antibiotic and bacteria. Thus far, most pharmacodynamic data reported have focused on fluoroquinolones, but work has been conducted on vancomycin, beta-lactams, macrolides, aminoglycosides, and other antibiotics. Despite the development of a number of different pharmacodynamic modeling systems, remarkable agreement exists between in vitro, animal, and limited human data. Although still somewhat premature and requiring additional clinical validation, antibiotic pharmacodynamics will likely advance on four fronts: the science should prove to be extremely useful and represent a cost-effective and efficient method to help develop new antibiotics; formulary committees will likely use pharmacodynamic parameters to assist in differentiating antibiotics of the same chemical class in making antibiotic formulary selections; pharmacodynamic principles will likely be used to design optimal antibiotic strategies for patients with severe infections; and limited data to date suggest that the application of pharmacodynamic concepts may limit or prevent the development of antibiotic resistance. The study of antibiotic pharmacodynamics appears to hold great promise and will likely become a routine part of our daily clinical practices.

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.

Pharmacokinetics and pharmacodynamics of cephalosporins in cerebrospinal fluid

Largely because of their low lipophilicity, cephalosporins poorly penetrate through the blood-brain barrier, achieving relatively low cerebrospinal fluid (CSF) concentrations. However, the minimum bactericidal concentrations (MBCs) of the extended spectrum cephalosporins for common meningeal pathogens are generally low; thus, therapeutic CSF drug concentrations several-fold greater than the MBC can be achieved with currently recommended dosage regimens. However, the effectiveness of cephalosporin therapy is unreliable in patients with meningitis caused by highly penicillin-resistant pneumococci. As in other body sites, the bactericidal activity of cephalosporins in CSF predominantly depends on the time their concentrations exceed the MBC of infecting organisms (t>MBC). Experimental studies show that, for maximal efficacy, t>MBC values greater than 90% of the dosage interval are required in meningitis. Such values are usually achieved in humans with currently recommended dosage regimens because the half-lives of cephalosporins are 2- to 3-fold longer in CSF than in serum. Several advanced generation cephalosporins have shown equal efficacy in clinical trials, but only cefotaxime, ceftriaxone and ceftazidime are currently approved for the treatment of patients with bacterial meningitis.

Antibiotic efficacy in vivo predicted by in vitro activity

A brief overview of arguments found in the literature is presented to apply the E(max) concept to experimental studies of antibiotics as well as to their clinical application. It may turn out to be more flexible than schedules based on arbitrary parameters that have the disadvantage that they have to be proven in each individual situation.

Evaluation of combined ceftriaxone and dexamethasone therapy in experimental cephalosporin-resistant pneumococcal meningitis

The treatment of meningitis caused by strains of Streptococcus pneumoniae with decreased susceptibility to third-generation cephalosporins is an increasingly frequent and difficult problem. In this study a rabbit model of meningitis was used to determine the efficacy of ceftriaxone at different dosages, and to establish the effect of the addition of dexamethasone to the chemotherapeutic regimen. Groups of eight rabbits were inoculated with 10(6) cfu/mL of a cephalosporin- resistant strain of S. pneumoniae (MIC of cefotaxime/ceftriaxone 2 mg/L). Eighteen hours after inoculation, ceftriaxone (50 or 100 mg/kg/day) with or without dexamethasone (0. 25 mg/kg/ day) was administered for a period of 48 h. The ceftriaxone dose of 50 mg/kg/day was not fully effective in this model (therapeutic failure rate 28%). With a dose of 100 mg/kg/day there were no therapeutic failures and all CSF cultures were below the level of detection at 48 h. CSF ceftriaxone concentrations, area under the time-concentration curve and time above the MIC were not significantly different with or without dexamethasone. However, concomitant use of dexamethasone resulted in higher CSF bacterial counts and a higher number of therapeutic failures (57% with the 50 mg/kg/day dose and 28% with the 100 mg/kg/day dose). Increasing doses of ceftriaxone might be an effective mode of therapy for meningitis caused by S. pneumoniae with MIC </= 2 mg/L. However, in contrast to cephalosporin-sensitive cases, in cases caused by ceftriaxone-resistant strains, concomitant use of dexamethasone was associated with a higher failure rate even when a higher dosage of ceftriaxone was used.

Advances in antimicrobial therapy

Despite several decades of improved therapy and prevention of infectious diseases, infectious pathogens remain major causes of morbidity and mortality in humans worldwide. Among the most complex and daunting problems facing medical science is the evolution of antibiotic resistance among many common and once easily-treated infectious agents. This review summarizes the status of newer antimicrobial agents that have utility against pathogens infecting the central nervous system.

Pharmacokinetics and pharmacodynamics of antibiotics in meningitis

The penetration of antimicrobials into the CSF is dependent on lipid solubility, molecular size, capillary and choroid plexus efflux pumps, protein binding, and the degree of inflammation. Penicillins, certain cephalosporins, carbapenems, fluoroquinolones, vancomycin, and rifampin provide the highest ratios of CSF levels to the MBC for common infecting organisms. For beta-lactam antibiotics, it is the duration of time that CSF concentrations exceed the MBC that determines the rate of bactericidal activity. It appears that levels should exceed the MBC for more than 50% of the dosing interval. The peak/MBC and AUC/MBC ratios are important determinants of efficacy for aminoglycosides and fluoroquinolones. Once-daily dosing of aminoglycosides is as effective as multiple-daily dosing regimens in experimental meningitis, probably because of drug-induced prolonged persistent effects. Fluoroquinolones do not produce as prolonged persistent effects and are slightly less effective when administered once daily. Although steroid use can reduce the penetration and decrease the bactericidal activity of some antimicrobials, such as vancomycin, in experimental meningitis, the clinical impact of steroid use in human meningitis is still unclear.

Emergence of drug resistance. Impact on bacterial meningitis

Antimicrobial resistance has emerged among the three major bacterial pathogens causing meningitis. Chloramphenicol resistance in the meningococcus recently has been described, and although intermediate penicillin resistance is common in some countries, the clinical importance of penicillin resistance in the meningococcus has yet to be established. Beta-lactamase-producing Haemophilus influenzae are relatively common, and chloramphenicol resistance is emerging. Third-generation cephalosporins are required to treat meningitis caused by these resistant strains. Pneumococcus resistance to penicillin and to chloramphenicol is widespread, and resistance to third-generation cephalosporins is found in many parts of the world. Correct management of these strains includes the addition of vancomycin or rifampin to therapy with third-generation cephalosporins.

Antimicrobial and anti-inflammatory treatment of bacterial meningitis

Mortality and morbidity rates of bacterial meningitis are still unacceptably high, and thus, new, potent antimicrobial agents and adjuvant anti-inflammatory strategies are being evaluated to improve patient outcome. With the declining rates of Haemophilus influenzae type B infections, after the introduction of conjugated vaccines, research to find preventive measures for Streptococcus pneumoniae and Neisseria meningitidis infections is underway. In the meantime, scientific effort is being directed optimally to treat disease caused by multiresistant pneumococcal strains.

Determinants of response to antibiotic therapy

The in vivo situation is far more complex than that of the standard in vitro susceptibility test yet in vitro tests have stood the test of time and are often good predictors of clinical outcome. Nevertheless, our understanding of the pharmacodynamics of antibiotic microbe interaction are giving us new insights into how to improve our performance and interpretation of these tests. These factors include consideration of inoculum effect, antibiotic interactions, cidal effects and the area under the inhibitory time curve (AUIC). There are however other variables which it is difficult to incorporate into in vitro tests, especially the immune status of the patient, which can be crucial to outcome. While the immune system can be boosted in certain instances, e.g. by growth factors or immunoglobulin infusions, our ability to modify the immune response to infection has been frustrated. Understanding the interaction of antibiotics with the immune system and the consequences of the differing actions of the various antibiotic classes on the immune response is another door that is opening for the future.

Pharmacokinetic optimisation of the treatment of bacterial central nervous system infections

Central nervous system (CNS) infections caused by bacteria with reduced sensitivity to antibacterials are an increasing worldwide challenge. In successfully treating these infections the following conditions should be considered: (i) Antibacterials do not distribute homogeneously in the central nervous compartments [cerebrospinal fluid (CSF), extracellular space of the nervous tissue, intracellular space of the neurons, glial cells and leucocytes]. Even within the CSF, after intravenous administration, a ventriculo-lumbar concentration gradient is often observed. (ii) Valid parameters of drug entry into the CSF are the CSF: serum concentration ratio in steady state and the CSF: serum ratio of the area under the concentration-time curves (AUCCSF/AUCS). Frequently, the elimination half-life (t1/2 beta) in CSF is longer than t1/2 beta in serum. (iii) For most antibacterials, lipophilicity, molecular weight and serum protein binding determine the drug entry into the CSF and brain tissue. With an intact blood-CSF and blood-brain barrier, the entry of hydrophilic antibacterials (beta-lactam antibacterials, glycopeptides) into the CNS compartments is poor and increases during meningeal inflammation. More lipophilic compounds [metronidazole, quinolones, rifampicin (rifampin) and chloramphenicol] are less dependent on the function of the blood-CSF and blood-brain barrier. (iv) Determination of the minimal inhibitory concentrations (MIC) of the causative organism is necessary for optimisation of treatment. (v) For rapid sterilisation of CSF, drug concentrations of at least 10 times MIC are required. The minimum CSF concentration: MIC ratio ensuring successful therapy is unknown. Strategies to achieve optimum antibacterial concentrations in the presence of minor disturbances of the blood-CSF and blood-brain barrier include, the increased use of low toxicity antibacterials (e.g., beta-lactam antibiotics), the use of moderately lipophilic compounds, and the combination of intravenous and intraventricular administration. Antibacterials which do not interfere with bacterial cell wall synthesis delay and/or decrease the liberation of proinflammatory bacterial products, delay or inhibit tumour necrosis factor release, and may reduce brain oedema in experimental meningitis. Conclusive evidence of the reduction of neuronal damage by this approach, however, is lacking.

Evaluation of moxifloxacin, a new 8-methoxyquinolone, for treatment of meningitis caused by a penicillin-resistant pneumococcus in rabbits

Moxifloxacin is a new 8-methoxyquinolone with high activity against gram-positive bacteria, including penicillin-resistant pneumococci. In an experimental meningitis model, we studied the pharmacokinetics of moxifloxacin in infected and uninfected rabbits and evaluated the antibiotic efficacies of moxifloxacin, ceftriaxone, and vancomycin against a penicillin-resistant Streptococcus pneumoniae strain (penicillin, ceftriaxone, vancomycin, and moxifloxacin MICs were 1, 0.5, 0.5, and 0.125 microgram/ml, respectively). Moxifloxacin entered cerebrospinal fluid (CSF) readily, with peak values within 15 to 30 min after bolus intravenous infusion and with a mean percent penetration into normal and purulent CSF of approximately 50 and 80%, respectively. The bactericidal effect of moxifloxacin was concentration dependent, and regrowth was seen only when the concentration of moxifloxacin in CSF was below the minimal bactericidal concentration. All antibiotic-treated groups (moxifloxacin given in two doses of 40 mg/kg of body weight, moxifloxacin in two 20-mg/kg doses, ceftriaxone in one 125-mg/kg dose, and vancomycin in two 20-mg/kg doses) had significantly higher reductions in CSF bacterial concentration than the untreated group (P < 0.05). Moxifloxacin was as effective as vancomycin and ceftriaxone in reducing bacterial counts at all time points tested (3, 5, 10, and 24 h). Moreover, moxifloxacin given in two 40-mg/kg doses resulted in a significantly higher reduction in CSF bacterial concentration (in log10 CFU per milliliter) than vancomycin within 3 h after the start of antibiotic treatment (3.49 [2.94 to 4.78] versus 2.50 [0.30 to 3.05]; P < 0.05). These results indicate that moxifloxacin could be useful in the treatment of meningitis, including penicillin-resistant pneumococcal meningitis.

Concentrations of cefpirome in cerebrospinal fluid of children with bacterial meningitis after a single intravenous dose

A single intravenous dose of cefpirome, 50 mg/kg, was administered to 15 children with bacterial meningitis 24 to 48 h after initiation of standard antibiotic and steroid therapy. Cefpirome concentrations in serum and cerebrospinal fluid were determined at selected time intervals. The mean (standard deviation) peak concentration in cerebrospinal fluid (n = 5) was 10.8 (7.8) microg/ml. Drug concentrations in cerebrospinal fluid above the MIC for Streptococcus pneumoniae at which 90% of the isolates were inhibited were found 2, 4, and 8 h after the dose of cefpirome was given. The penetration of cefpirome into cerebrospinal fluid compares favorably with that of other extended-spectrum cephalosporins and suggests that this agent would be useful in the therapy of childhood meningitis, including cases caused by drug-resistant S. pneumoniae.