Pharmacokinetics and pharmacodynamics of cephalosporins in cerebrospinal fluid

Ceftazidime-related neurotoxicity in a patient with renal impairment: a case report and literature review

PURPOSE

We present the case of a 67-year-old woman with severely reduced renal clearance suffering from ceftazidime-induced encephalopathy. Subsequently, we search the literature to review and describe the neurotoxicity of ceftazidime.

METHODS

A search string was developed to search PubMed for relevant cases from which relevant information was extracted. Using the collected data a ROC analysis was performed in R to determine a neurotoxicity threshold.

RESULTS

Our patient suffered from progressive loss of consciousness and myoclonic seizures, with improvements noted a few days after discontinuation of treatment. The dose was not appropriately reduced to take into account her reduced renal function. The highest ceftazidime concentration recorded was 234.9 mg/mL. Using the Naranjo score we found a probable relationship between our patient's encephalopathy and ceftazidime administration. In the literature we found a total of 32 similar cases, most of which also had some form of renal impairment. Using our collected data and ceftazidime concentrations provided in the literature, a ROC analysis provided a neurotoxicity threshold of 78 mg/L for ceftazidime neurotoxicity.

CONCLUSION

Ceftazidime-related neurotoxicity is a known issue, especially in patients with severe renal impairment. Yet no concrete toxicity threshold has been reported so far. We propose the first toxicity threshold for ceftazidime of 78 mg/L. Future prospective studies are needed to validate and optimize the neurotoxicity threshold as upper limit for ceftazidime therapeutic drug monitoring.

Ceftriaxone alters the gut microbiome composition and reduces alcohol intake in male and female Sprague-Dawley rats

Ceftriaxone is an antibiotic that increases central nervous system (CNS) protein expression of the glutamate transporters GLT-1 and xCT and ameliorates pathological behaviors in rodent models of neurological disease and substance use disorder. However, little ceftriaxone passes through the blood-brain-barrier, the CNS binding partner of ceftriaxone is unknown, and ceftriaxone does not consistently upregulate GLT-1 and xCT in cell culture. Ceftriaxone alters the gut microbiome composition in rodents and humans, and the microbiome-gut-brain axis regulates drug-seeking. Thus, here we test the hypothesis that ceftriaxone reduces alcohol intake while ameliorating alcohol-induced disruption of the gut microbiome composition. Male and female Sprague-Dawley rats received intermittent access to alcohol (IAA) while controls received access to only water. Following 17 IAA sessions, ceftriaxone/vehicle treatment was given for 5 days. Analysis of the gut microbiome composition was assessed by 16S rRNA gene amplicon sequencing conducted on fecal pellets collected prior to and after alcohol consumption and following ceftriaxone treatment. Male rats displayed escalated alcohol intake and preference over the course of the 17 sessions; however, total alcohol intake did not differ between the sexes. Ceftriaxone reduced alcohol intake and preference in male and female rats. While alcohol affected a diverse set of amplicon sequencing variants (ASV), ceftriaxone markedly reduced the diversity of microbial communities reflected by a blooming of the Enterococcaceae family. The remaining effects of ceftriaxone, however, encompassed families both affected and unaffected by prior alcohol drinking and highlight the Ruminococcaceae and Muribaculaceae families as bidirectionally modulated by alcohol and ceftriaxone. Altogether, our study confirms that ceftriaxone reduces alcohol intake in rats and partially reverses alcohol-induced dysbiosis.

Molecular Mechanisms of Organic Anion Transporting Polypeptide-Mediated Organic Anion Clearance at the Blood-Cerebrospinal Fluid Barrier

The blood-cerebrospinal fluid barrier (BCSFB), formed by the choroid plexus epithelial (CPE) cells, plays an active role in removing drugs and metabolic wastes from the brain. Recent functional studies in isolated mouse choroid plexus (CP) tissues suggested the presence of organic anion transporting polypeptides (OATPs, encoded by SLCOs) at the apical membrane of BCSFB, which may clear large organic anions from the cerebrospinal fluid (CSF). However, the specific OATP isoform involved is unclear. Using quantitative fluorescence imaging, we showed that the fluorescent anions sulforhodamine 101 (SR101), fluorescein methotrexate (FL-MTX), and 8-fluorescein-cAMP (fluo-cAMP) are actively transported from the CSF to the subepithelial space in CP tissues isolated from wild-type mice. In contrast, transepithelial transport of these compounds across the CPE cells was abolished in Oatp1a/1b-/- mice due to impaired apical uptake. Using transporter-expressing cell lines, SR101, FL-MTX, and fluo-cAMP were additionally shown to be transported by mouse OATP1A5 and its human counterpart OATP1A2. Kinetic analysis showed that estrone-3-sulfate and SR101 are transported by OATP1A2 and OATP1A5 with similar Michaelis-Menten constants (Km). Immunofluorescence staining further revealed the presence of OATP1A2 protein in human CP tissues. Together, our results suggest that large organic anions in the CSF are actively transported into CPE cells by apical OATP1A2 (OATP1A5 in mice), then subsequently effluxed into the blood by basolateral multidrug resistance-associated proteins (MRPs). As OATP1A2 transports a wide array of endogenous compounds and xenobiotics, the presence of this transporter at the BCSFB may imply a novel clearance route for drugs and neurohormones from the CSF. SIGNIFICANCE STATEMENT: Drug transporters at the blood-cerebrospinal fluid (CSF) barrier play an important but understudied role in brain drug disposition. This study revealed a functional contribution of rodent organic anion transporting polypeptide (OATP) 1A5 towards the CSF clearance of organic anions and suggested a similar role for OATP1A2 in humans. Delineating the molecular mechanisms governing CSF organic anion clearance may help to improve the prediction of central nervous system (CNS) pharmacokinetics and identify drug candidates with favorable CNS pharmacokinetic properties.

Validated HPLC method for ceftriaxone from dried blood spots for pharmacokinetic studies and therapeutic drug monitoring in neonatal population

Background: Pharmacokinetic evaluation is essential for the precise dosing of ceftriaxone in neonates. There is a need for developing a sensitive, affordable and convenient analytical method that can estimate ceftriaxone from dried blood spot (DBS) samples of neonates. Method: An HPLC-UV method was developed and validated as per ICH M10 for ceftriaxone from DBS and plasma using an Inertsil-ODS-3V column with gradient elution. DBS samples were extracted with methanol. Clinical validation was performed using neonatal samples. Results: The developed plasma- and DBS-based-HPLC method were linear from 2-700 μg/ml and 2-500 μg/ml, respectively, for ceftriaxone. Bland-Altman analysis indicated a strong interconvertibility between the plasma and DBS assays. Conclusion: Observed concentrations in clinical samples were comparable to the predicted concentrations, proving the clinical validity of the method.

Penicillin-Susceptible Streptococcus pneumoniae Meningitis in Adults: Does the Ceftriaxone Dosing Matter?

The recommended empiric ceftriaxone dosing regimen for acute bacterial meningitis in adults is 2 g every 12 h. After penicillin-susceptible Streptococcus pneumoniae is isolated as a causative microorganism, the ceftriaxone dose may be continued or reduced to a single dose of 2 g every 24 h, per institutional preference. There is no clear guidance that indicates the superiority of one regimen over the other. The objective of this study was to evaluate the susceptibility of S. pneumoniae in the cerebral spinal fluid (CSF) of patients with meningitis and the relationship between ceftriaxone dose and clinical outcomes. We identified 52 patients with S. pneumoniae meningitis with positive CSF cultures who were treated at the University Hospital, Bern, Switzerland, over a 19-year period. We collected clinical and microbiological data for evaluation. Broth microdilution and Etest methods were performed to test penicillin and ceftriaxone susceptibility. All isolates were susceptible to ceftriaxone. Ceftriaxone was empirically used in 50 patients, with a starting dosing regimen of 2 g every 24 h in 15 patients and 2 g every 12 h in 35 patients. In 32 patients started on a twice-daily regimen (91%), doses were reduced to once daily after a median of 1.5 (95% CI 1-2) days. The overall in-hospital mortality was 15.4% (n = 8), and 45.7% of patients reported at least one sequela of meningitis at the last follow-up (median 375, 95% CI 189-1585 days). We found no statistical difference in outcome between the 2 g every 24 h and the 2 g every 12 h ceftriaxone dosing regimens. A ceftriaxone total daily dose of 2 g may be associated with similar outcomes to a 4 g total daily dose, provided that the causative organism is highly susceptible to ceftriaxone. The persistence of neurological and infection sequelae at the last follow-up underscores the need for optimal treatment of these complex infections.

Cefazolin in the treatment of central nervous system infections: A narrative review and recommendation

Infections of the central nervous system (CNS) are complex to treat and associated with significant morbidity and mortality. Historically, antistaphylococcal penicillins such as nafcillin were recommended for the treatment of methicillin-susceptible staphylococcal CNS infections. However, the use of antistaphylococcal penicillins presents challenges, such as frequent dosing administration and adverse events with protracted use. This narrative reviews available clinical and pharmacokinetic/pharmacodynamic (PK/PD) data for cefazolin in CNS infections and produces a recommendation for use. Based on the limited available evidence analyzed, dose optimized cefazolin is likely a safe and effective alternative to antistaphylococcal penicillins for a variety of CNS infections due to methicillin-susceptible Staphylococcus aureus. Given the site of infection and wide therapeutic index of cefazolin, practitioners may consider dosing cefazolin regimens of 2 g IV every 6 h or a continuous infusion of 8-10 g daily instead of 2 g IV every 8 h to optimize PK/PD properties.

Treatment options for neonatal infections in the post-cefotaxime era

INTRODUCTION

: Cefotaxime has been used for the management of neonatal infections since the 1990s for suspected meningitis and to mitigate gentamicin-associated renal injury. Its shortage in 2015 and subsequent removal from the U.S. pharmaceutical market forced providers to consider alternatives. Ceftriaxone, a cephalosporin with an identical antibacterial spectrum of activity to cefotaxime, is contraindicated in neonates due to its risk of biliary pseudolithiasis. Ceftazidime was recommended as an alternative by the American Academy of Pediatrics but is inequivalent.

AREAS COVERED

: This article addresses indications for cephalosporin use and considerations when selecting an alternative to cefotaxime. Differences among cefotaxime, ceftriaxone, ceftazidime, and cefepime are discussed and compared to the standard-of-care presumptive regimen, ampicillin and gentamicin. The authors consider the data behind the neonatal contraindication to ceftriaxone and provide recommendations for their application to practice.

EXPERT OPINION

: The data against ceftriaxone use in neonates remain poor, particularly in the context of the cefotaxime shortage and lack of an equivalent alternative. Ceftriaxone could be considered in low-risk neonates without hyperbilirubinemia or exposure to calcium-containing fluids on a case-by-case basis. Ceftazidime monotherapy for presumptive management of neonatal infections is inappropriate; cefepime should be more frequently utilized in neonates who are poor candidates for ceftriaxone.

Ceftazidime dosing in obese patients: is it time for more?

INTRODUCTION

Ceftazidime is used for the treatment of many bacterial infections, including severe P. aeruginosa infections. Like other beta-lactams, inter-individual variability in ceftazidime pharmacokinetics has been described. Due to its related pathophysiological modifications, obesity might influence ceftazidime pharmacokinetics.

AREAS COVERED

The objective of this review is to assess the current state of knowledge about the impact of obesity on ceftazidime treatment. A literature search was conducted on PubMed-MEDLINE (2016-2021) to retrieve pharmacokinetic studies published in English, matching the terms 'ceftazidime' AND 'pharmacokinetics.'

EXPERT OPINION

The impact of obesity on pharmacokinetics is generally poorly known, mainly because obese patients are often excluded from clinical studies. However, the published literature clearly shows that obese patients have significantly lower ceftazidime concentrations. This could be explained by increased volume of distribution and clearance. This low exposure represents a major factor of therapeutic failure, potentially fatal for critically ill patients. While further studies would be useful to better assess the magnitude and understanding of this variability, the use of higher doses of ceftazidime is needed in obese patients. Moreover, therapeutic drug monitoring for dose adaptation is of major interest for these patients, as the efficacy of ceftazidime seems to be directly related to its plasma concentration.

Ceftazidime and cefepime antagonize 5-fluorouracil's effect in colon cancer cells

Background

Drug-drug interaction (DDI), which can occur at the pharmacokinetics and/or the pharmacodynamics (PD) levels, can increase or decrease the therapeutic or adverse response of a drug itself or a combination of drugs. Cancer patients often receive, along their antineoplastic agents, antibiotics such as ß-lactams to treat or prevent infection. Despite the narrow therapeutic indices of antibiotics and antineoplastic agents, data about their potential interaction are insufficient. 5-fluorouracil (5-FU), widely used against colon cancer, is known for its toxicity and large intra- and inter- individual variability. Therefore, knowledge about its interaction with antibiotics is crucial.

Methods

In this study, we evaluated at the PD levels, against HCT-116 colon cancer cells, DDI between 5-FU and several ß-lactams (ampicillin, benzypenicillin, piperacillin, meropenem, flucloxacillin, ceftazidime (CFT), and cefepime (CFP)), widely used in intensive care units. All drugs were tested at clinically achieved concentrations. MTT assay was used to measure the metabolic activity of the cells. Cell cycle profile and apoptosis induction were monitored, in HCT-116 and DLD-1 cells, using propidium iodide staining and Caspase-3/7 activity assay. The uptake of CFT and CFP by the cells was measured using LC-MS/MS method.

Results

Our data indicate that despite their limited uptake by the cells, CFT and CFP (two cephalosporins) antagonized significantly 5-FU-induced S-phase arrest (DLD-1 cells) and apoptosis induction (HCT-116 cells). Remarkably, while CFP did not affect the proliferation of colon cancer cells, CFT inhibited, at clinically relevant concentrations, the proliferation of DLD-1 cells via apoptosis induction, as evidenced by an increase in caspase 3/7 activation. Unexpectedly, 5-FU also antagonized CFT’s induced cell death in DLD-1 cells.

Conclusion

This study shows that CFP and CFT have adverse effects on 5-FU’s action while CFT is a potent anticancer agent that inhibits DLD-1 cells by inducing apoptotic cell death. Further studies are needed to decipher the mechanism(s) responsible for CFT’s effects against colon cancer as well as the observed antagonism between CFT, CFP, and 5-FU with the ultimate aim of translating the findings to the clinical settings.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-09125-4.

Ceftriaxone treatment of syphilis

The article presents literature data on the use of antibacterial drugs for the treatment of patients with syphilis, where the main focus is on ceftriaxone. Based on the materials of national and foreign studies, data on the effectiveness of ceftriaxone in the treatment of patients with various forms of syphilis have been analyzed, and information characterizing the pharmacological and pharmacokinetic features of ceftriaxone has been presented. Based on the scientific and clinical experience accumulated over previous years, both in Russia and abroad, some results of the use of ceftriaxone in the treatment of syphilis have been summed up. To search for the necessary literature, the PubMed, MedLine, Web of Science and RSCI databases were used.

Ceftazidime-Induced Neurotoxicity in an 80-Year-Old Female With Renal Dysfunction: A Case Report

Neurological toxicity is a relatively rare adverse reaction reported in elderly patients treated with cephalosporins. We present a case of ceftazidime-induced encephalopathy in the context of acute kidney injury in an 80-year-old female treated for a Pseudomonas aeruginosa prosthetic joint infection. During the course of treatment, the patient developed sudden confusion and disorientation. The patient's mental state progressively worsened, eventually leading to intubation and admission to the intensive care unit. As imaging and laboratory analyses revealed no alternative causes explaining the patient's symptoms, ceftazidime was stopped under the suspicion of drug-induced neurotoxicity. Shortly after ceftazidime discontinuation, the patient's condition drastically improved and returned to baseline within 5 days. This case reveals the potential severity of cephalosporin-induced neurotoxicity in elderly patients and highlights the importance of quickly detecting such adverse events in order to prevent dire outcomes.

Safety of ceftriaxone in paediatrics: a systematic review

OBJECTIVE

To determine the safety of ceftriaxone in paediatric patients and systematically evaluate the categories and incidences of adverse drug reactions (ADRs) of ceftriaxone in paediatric patients.

METHODS

We performed a systematic search in Medline, PubMed, Cochrane Central Register of Controlled Trials, EMBASE, CINAHL, International Pharmaceutical Abstracts and bibliographies of relevant articles up to December 2018 for all types of studies that assessed the safety of ceftriaxone in paediatric patients aged ≤18 years.

RESULTS

112 studies met the inclusion criteria involving 5717 paediatric patients who received ceftriaxone and reported 1136 ADRs. The most frequent ADRs reported in prospective studies were gastrointestinal (GI) disorders (37.4 %, 292/780), followed by hepatobiliary disorders (24.6%, 192/780). Serious ADRs leading to withdrawal or discontinuation of ceftriaxone were reported in 86 paediatric patients. Immune haemolytic anaemia (34.9%, 30/86) and biliary pseudolithiasis (26.7%, 23/86) were the two major causes. Haemolytic anaemia following intravenous ceftriaxone led to death in 11 children whose primary disease was sickle cell disease. Almost all biliary pseudolithiasis are reversible. However, the incidence was high affecting one in five paediatric patients (20.7%).

CONCLUSIONS

GI ADRs are the most common toxicity of ceftriaxone in paediatric patients. Immune haemolytic anaemia and biliary pseudolithiasis are the most serious ADRs and the major reasons for discontinuation of ceftriaxone. Immune haemolytic anaemia is more likely in children with sickle cell disease and may cause death. Ceftriaxone should be used with caution in children with sickle cell disease.

TRIAL REGISTRATION NUMBER

CRD42017055428.

Antifungal drugs: An updated review of central nervous system pharmacokinetics

Invasive fungal infections (IFIs) in the central nervous system (CNS) are particularly hard to treat and are associated with high morbidity and mortality rates. Four chemical classes of systemic antifungal agents are used for the treatment of IFIs (eg meningitis), including polyenes, triazoles, pyrimidine analogues and echinocandins. This review will address all of these classes and discuss their penetration and accumulation in the CNS. Treatment of fungal meningitis is based on the antifungal that shows good penetration and accumulation in the CNS. Pharmacokinetic data concerning the entry of antifungal agents into the intracranial compartments are faulty. This review will provide an overview of the ability of systemic antifungals to penetrate the CNS, based on previously published drug physicochemical properties and pharmacokinetic data, for evaluation of the most promising antifungal drugs for the treatment of fungal CNS infections. The studies selected and discussed in this review are from 1990 to 2019.

Prolonged infusion of linezolid is associated with improved pharmacokinetic/pharmacodynamic (PK/PD) profiles in patients with external ventricular drains

OBJECTIVE

We previously investigated the pharmacokinetic and pharmacodynamic (PK/PD) parameters of routine linezolid infusions (1 h) in patients with external ventricular drains (EVD). The aim of the study was to determine whether extended linezolid infusions (200 mg/h for 3 h) were more efficacious than short linezolid infusions (600 mg/h for 1 h).

METHODS

We collected cerebrospinal fluid (CSF) and plasma samples from 10 patients who received linezolid infusions after cerebral hemorrhage surgery with EVDs. Linezolid concentrations were measured by high-performance liquid chromatography (HPLC). A Monte Carlo simulation was used to measure the probability of target attainments (PTA) and the PK/PD indexes at four minimum inhibitory concentrations (MIC).

RESULTS

When the same dose (600 mg) was given as an extended infusion (3 h), linezolid reached its maximum concentrations in the plasma and CSF at 3.00 h and 4.40 h, respectively. The mean penetration of linezolid in CSF was 41.31%. Using the parameter of AUC_{0-24 h}/MIC ≥ 100, the plasma PTA provided good coverage at > 90% when MIC was ≤ 1 μg/mL, while the values were 0 in CSF. Using the parameter %T (time) > MIC ≥ 85%, the PTA in both the plasma and CSF provided good coverage when MIC ≤ 2 μg/mL. Compared with routine infusions, prolonged infusion times (3 h) showed increased PTA of linezolid.

CONCLUSIONS

Prolonged infusion times increased the concentration of linezolid in the plasma, leading to improved therapeutic outcomes. However, this improvement did not exist in CSF. Lastly, the PK/PD indicator AUC/MIC ≥ 100 may be used to achieve improved outcomes in patients with critical infections.

Phenotypic assays in yeast and zebrafish reveal drugs that rescue ATP13A2 deficiency

Mutations in ATP13A2 (PARK9) are causally linked to the rare neurodegenerative disorders Kufor-Rakeb syndrome, hereditary spastic paraplegia and neuronal ceroid lipofuscinosis. This suggests that ATP13A2, a lysosomal cation-transporting ATPase, plays a crucial role in neuronal cells. The heterogeneity of the clinical spectrum of ATP13A2-associated disorders is not yet well understood and currently, these diseases remain without effective treatment. Interestingly, ATP13A2 is widely conserved among eukaryotes, and the yeast model for ATP13A2 deficiency was the first to indicate a role in heavy metal homeostasis, which was later confirmed in human cells. In this study, we show that the deletion of YPK9 (the yeast orthologue of ATP13A2) in Saccharomyces cerevisiae leads to growth impairment in the presence of Zn2+, Mn2+, Co2+ and Ni2+, with the strongest phenotype being observed in the presence of zinc. Using the ypk9Δ mutant, we developed a high-throughput growth rescue screen based on the Zn2+ sensitivity phenotype. Screening of two libraries of Food and Drug Administration-approved drugs identified 11 compounds that rescued growth. Subsequently, we generated a zebrafish model for ATP13A2 deficiency and found that both partial and complete loss of atp13a2 function led to increased sensitivity to Mn2+. Based on this phenotype, we confirmed two of the drugs found in the yeast screen to also exert a rescue effect in zebrafish-N-acetylcysteine, a potent antioxidant, and furaltadone, a nitrofuran antibiotic. This study further supports that combining the high-throughput screening capacity of yeast with rapid in vivo drug testing in zebrafish can represent an efficient drug repurposing strategy in the context of rare inherited disorders involving conserved genes. This work also deepens the understanding of the role of ATP13A2 in heavy metal detoxification and provides a new in vivo model for investigating ATP13A2 deficiency.

La pharmacologie des antibiotiques dans le liquide cérébrospinal

Le liquide cérébrospinal (LCS) est produit par les plexus choroïdes des ventricules cérébraux avec pour rôle de protéger le système nerveux central des agressions mécaniques (chocs) et infectieuses (virus, bactéries, parasites) et de lui apporter des nutriments essentiels à son fonctionnement optimal. Il est anatomiquement à l'interface entre le compartiment sanguin, le liquide interstitiel cérébral et le compartiment lymphatique. Sa composition est fortement influencée par ces structures. Deux barrières permettent de réguler le passage moléculaire dans le système nerveux central et limitent fortement l'accès à ce dernier : la barrière hématoencéphalique et la barrière hématoméningée. La diffusion des antibiotiques dans le LCS, mais également dans le parenchyme cérébral dépend de plusieurs facteurs : la taille de la molécule, sa lipophilie, la liaison aux protéines plasmatiques et l'intégrité des barrières hématoencéphalique et hématoméningée. Les phénomènes d'inflammation méningée observés dans les méningites bactériennes augmentent la perméabilité des barrières et facilitent la diffusion des agents antibiotiques. Les molécules diffusant le mieux dans le LCS sont les fluoroquinolones, le linézolide, l'association triméthoprime- sulfaméthoxazole, la rifampicine et la fosfomycine. Les bêtalactamines présentent une diffusion assez faible mais qui augmente fortement en cas d'inflammation méningée. Des posologies journalières très élevées permettent de contourner l'écueil de la diffusion. De nombreux paramètres influencent la diffusion des antibiotiques dans le LCS. Le choix de l'antibiothérapie adaptée se fait en fonction de ces paramètres et du type d'infection à traiter en concertation pluridisciplinaire.

Cefepime neurotoxicity: thresholds and risk factors. A retrospective cohort study

OBJECTIVES

Toxic serum cefepime trough concentrations are not well defined in the current literature. We aimed to define a more precise plasma trough concentration threshold for this antibiotic's neurological toxicity and to identify individuals at risk for developing neurotoxic side effects.

METHODS

Retrospective study including all individuals who underwent cefepime therapeutic drug monitoring (TDM) between 2013 and 2017. Individuals with cefepime concentrations other than trough were excluded. The primary outcome was to assess the incidence of neurotoxicity and its relationship with cefepime plasma trough concentrations. Secondary outcomes were the relationship of renal function, cefepime daily dose, age, and cerebral and general co-morbidities with the occurrence of neurotoxicity. We also compared the mortality rate during hospitalization in individuals with and without neurotoxicity, and the possible impact of neuroprotective co-medications on outcomes.

RESULTS

Cefepime concentrations were determined in 584 individuals. Among 319 individuals with available trough concentrations included, the overall incidence of neurotoxicity was 23.2% (74 of 319 individuals). Higher cefepime plasma trough concentrations were significantly associated with risk of neurotoxicity (no neurotoxicity 6.3 mg/L (interquartile range (IQR) 4.1-8.6) versus with neurotoxicity 21.6 mg/L (IQR 17.0-28.6), p <0.001). Individuals with presumed cefepime neurotoxicity had a significantly lower renal function (estimated glomerular filtration rate 82.0 mL/min/1.73 m² (IQR 45.0-105.0) versus 35.0 mL/min/1.73 m² (IQR 23.3-53.3], p <0.001), and significantly higher in-hospital mortality (19 (7.8%) versus 26 (35.1%) individuals, p <0.001). No neurotoxic side effects were seen below a trough concentration of 7.7 mg/L. Levels ≥38.1 mg/L always led to neurological side effects.

CONCLUSION

In individuals with risk factors for cefepime neurotoxicity, such as renal insufficiency, TDM should be systematically performed, aiming at trough concentrations <7.5 mg/L.

Optimization of the treatment with beta-lactam antibiotics in critically ill patients-guidelines from the French Society of Pharmacology and Therapeutics (Société Française de Pharmacologie et Thérapeutique-SFPT) and the French Society of Anaesthesia and Intensive Care Medicine (Société Française d'Anesthésie et Réanimation-SFAR)

BACKGROUND

Beta-lactam antibiotics (βLA) are the most commonly used antibiotics in the intensive care unit (ICU). ICU patients present many pathophysiological features that cause pharmacokinetic (PK) and pharmacodynamic (PD) specificities, leading to the risk of underdosage. The French Society of Pharmacology and Therapeutics (SFPT) and the French Society of Anaesthesia and Intensive Care Medicine (SFAR) have joined forces to provide guidelines on the optimization of beta-lactam treatment in ICU patients.

METHODS

A consensus committee of 18 experts from the two societies had the mission of producing these guidelines. The entire process was conducted independently of any industry funding. A list of questions formulated according to the PICO model (Population, Intervention, Comparison, and Outcomes) was drawn-up by the experts. Then, two bibliographic experts analysed the literature published since January 2000 using predefined keywords according to PRISMA recommendations. The quality of the data identified from the literature was assessed using the GRADE® methodology. Due to the lack of powerful studies having used mortality as main judgement criteria, it was decided, before drafting the recommendations, to formulate only "optional" recommendations.

RESULTS

After two rounds of rating and one amendment, a strong agreement was reached by the SFPT-SFAR guideline panel for 21 optional recommendations and a recapitulative algorithm for care covering four areas: (i) pharmacokinetic variability, (ii) PK-PD relationship, (iii) administration modalities, and (iv) therapeutic drug monitoring (TDM). The most important recommendations regarding βLA administration in ICU patients concerned (i) the consideration of the many sources of PK variability in this population; (ii) the definition of free plasma concentration between four and eight times the Minimal Inhibitory Concentration (MIC) of the causative bacteria for 100% of the dosing interval as PK-PD target to maximize bacteriological and clinical responses; (iii) the use of continuous or prolonged administration of βLA in the most severe patients, in case of high MIC bacteria and in case of lower respiratory tract infection to improve clinical cure; and (iv) the use of TDM to improve PK-PD target achievement.

CONCLUSIONS

The experts strongly suggest the use of personalized dosing, continuous or prolonged infusion and therapeutic drug monitoring when administering βLA in critically ill patients.

Potential role of the Virchow Robin space in the pathogenesis of bacterial meningitis

Meningitis is an infectious disease commonly arising from a bacterial etiology. The rapid progression of morbidity and mortality due to bacterial meningitis requires critical and imminent time-dependent clinical intervention. Although it is unambiguously clear that bacteria must infiltrate the cerebrospinal fluid, the sequence of events in the pathogenesis of bacterial meningitis has not been fully elucidated. Most reviews of the pathogenesis of bacterial meningitis do not specify the anatomical location of bacteria following BBB traversal. We propose an additional hypothesis focusing on the Virchow-Robin space (VRS). The VRS consists of a small, but identifiable perivascular space formed by a sheath of cells derived from the pia mater. The VRS has been described as an immunological space and possibly having a role in several neuropathological diseases. Solute exchange between cerebrospinal fluid and extracellular fluid occurs at the VRS, with subsequent drainage into the subarachnoid space. Because the VRS is continuous with the subpial space, a more direct route to the meninges is facilitated. The involvement of the VRS may have profound implications on the pathogenesis and therapeutic strategies: (1) nasopharyngeal colonization; (2) penetration into the blood stream after crossing the mucosal and epithelial membranes; (3) proliferation in the bloodstream; (4) extravasations through the endothelium of the post-capillary venules to the perivascular VRS; (5) migration from VRS to subpial space; (6) traversal through pia mater, entering the CSF in the subarachnoid space; (7) invasion of the meninges. The implication of the VRS in the pathogenesis of bacterial meningitis would be twofold. First, the VRS could provide an additional route of entry of bacteria into the brain. Second, the VRS could provide an area for bacterial proliferation, and thereby serve as a bacterial reservoir in relatively close proximity to the meninges. The clinical consequences of this hypothesis are: 1) clinical interpretation of laboratory findings, and 2) effective antibiotic delivery into the VRS. If the role of the VRS is established as part of bacterial meningitis pathogenesis, antibiotic pharmacokinetics and pharmacodynamics in the VRS need to be determined. This may result in developing novel antibiotic delivery and clinical strategies to improve morbidity and mortality.

Cefazolin versus anti-staphylococcal penicillins for treatment of methicillin-susceptible Staphylococcus aureus bacteraemia: a narrative review

BACKGROUND

Anti-staphylococcal penicillins (ASPs) are recommended as first-line agents in methicillin-susceptible Staphylococcus aureus (MSSA) bacteraemia. Concerns about their safety profile have contributed to the increased use of cefazolin. The comparative clinical effectiveness and safety profile of cefazolin versus ASPs for such infections remain unclear. Furthermore, uncertainty persists concerning the use of cefazolin due to controversies over its efficacy in deep MSSA infections and its possible negative ecological impact.

AIMS

The aim of this narrative review was to gather and balance available data on the efficacy and safety of cefazolin versus ASPs in the treatment of MSSA bacteraemia and to discuss the potential negative ecological impact of cefazolin.

SOURCES

PubMed and EMBASE electronic databases were searched up to May 2017 to retrieve available studies on the topic.

CONTENTS

Although described in vitro and in experimental studies, the clinical relevance of the inoculum effect during cefazolin treatment of deep MSSA infections remains unclear. It appears that there is no significant difference in rate of relapse or mortality between ASPs and cefazolin for the treatment of MSSA bacteraemia but these results should be cautiously interpreted because of the several limitations of the available studies. Compared with cefazolin, there is more frequent discontinuation for adverse effects with ASP use, especially because of cutaneous and renal events. No study has evidenced any change in the gut microbiota after the use of cefazolin.

IMPLICATIONS

Based on currently available studies, there are no data that enable a choice to be made of one antibiotic over the other except in patients with allergy or renal impairment. This review points out the need for future prospective studies and randomized controlled trials to better address these questions.

Systemic pharmacokinetics and cerebrospinal fluid uptake of intravenous ceftriaxone in patients with amyotrophic lateral sclerosis

The cephalosporin antibiotic ceftriaxone was evaluated as a potential therapeutic agent for the treatment of amyotrophic lateral sclerosis (ALS). The pharmacokinetics (PK) of ceftriaxone in plasma and cerebrospinal fluid (CSF) were investigated in 66 participants in a previously reported clinical trial. Their mean age was 51 years, and 65% were male. Participants were randomly assigned to 1 of 3 treatment groups receiving intravenous infusions (mean duration: 25 minutes) every 12 hours of either: placebo and placebo; 2 g ceftriaxone and placebo; or 2 g ceftriaxone twice. Mean steady-state plasma PK variables were: volume of distribution, 14 L (0.17 L/kg); elimination half-life, 8-9 h; total clearance, 17-21 mL/min (0.22-0.25 mL/min/kg). Values were not different between dosage groups. CSF PK analysis, determined through sparse CSF sampling, indicated apparent entry and elimination half-life values of 1.0 and 34 hours, respectively. With both dosage regimens, CSF concentrations were maintained above the target threshold of 1.0 µM (0.55 µg/mL) as determined from in vitro models. The plasma and CSF PK profiles of ceftriaxone were used as a basis for planning the Phase 3 clinical trial of ceftriaxone in ALS.

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.

Adenosine and glutamate in neuroglial interaction: implications for circadian disorders and alcoholism

Recent studies have demonstrated that the function of glia is not restricted to the support of neuronal function. In fact, astrocytes are essential for neuronal activity in the brain and play an important role in the regulation of complex behavior. Astrocytes actively participate in synapse formation and brain information processing by releasing and uptaking glutamate, D-serine, adenosine 5'-triphosphate (ATP), and adenosine. In the central nervous system, adenosine-mediated neuronal activity modulates the actions of other neurotransmitter systems. Adenosinergic fine-tuning of the glutamate system in particular has been shown to regulate circadian rhythmicity and sleep, as well as alcohol-related behavior and drinking. Adenosine gates both photic (light-induced) glutamatergic and nonphotic (alerting) input to the circadian clock located in the suprachiasmatic nucleus of the hypothalamus. Astrocytic, SNARE-mediated ATP release provides the extracellular adenosine that drives homeostatic sleep. Acute ethanol increases extracellular adenosine, which mediates the ataxic and hypnotic/sedative effects of alcohol, while chronic ethanol leads to downregulated adenosine signaling that underlies insomnia, a major predictor of relapse. Studies using mice lacking the equilibrative nucleoside transporter 1 have illuminated how adenosine functions through neuroglial interactions involving glutamate uptake transporter GLT-1 [referred to as excitatory amino acid transporter 2 (EAAT2) in human] and possibly water channel aquaporin 4 to regulate ethanol sensitivity, reward-related motivational processes, and alcohol intake.

Glutamate transporter 1: target for the treatment of alcohol dependence

Emerging evidence indicates that many aspects of alcohol and drug dependence involve changes in glutamate transmission. A number of studies have reported that drugs of abuse, including alcohol and cocaine, alter glutamate transport. Extracellular glutamate is regulated by a number of glutamate transporters in various brain regions. Of these transporters, glutamate transporter (GLT1) is a key player in the removal of most of the extracellular glutamate. Similar to neurodegenerative disease models, in which there is dysfunction of the glutamatergic excitatory system, the role of GLT1 has been tested in drug dependence models that show dysfunction of glutamate transmission. We and others have recently found that ceftriaxone, an FDA-approved drug known to elevate GLT1 expression, attenuates cue-induced cocaine relapse. Moreover, we recently found that alcohol-preferring rats treated with ceftriaxone showed a significant dosedependent reduction in alcohol consumption. We also demonstrated that ceftriaxone-induced upregulation of GLT1 expression was associated with increases in glutamate uptake in Huntington's disease mouse model. Importantly, ceftriaxone is currently in clinical trials for the treatment of amyotrophic lateral sclerosis. This review provides information about the potential therapeutic role of GLT1 for the treatment of alcohol abuse and dependence.

Microdialysis study of cefotaxime cerebral distribution in patients with acute brain injury

Central nervous system (CNS) antibiotic distribution was described mainly from cerebrospinal fluid data, and only few data exist on brain extracellular fluid concentrations. The aim of this study was to describe brain distribution of cefotaxime (2 g/8 h) by microdialysis in patients with acute brain injury who were treated for a lung infection. Microdialysis probes were inserted into healthy brain tissue of five critical care patients. Plasma and unbound brain concentrations were determined at steady state by high-performance liquid chromatography. In vivo recoveries were determined individually using retrodialysis by drug. Noncompartmental and compartmental pharmacokinetic analyses were performed. Unbound cefotaxime brain concentrations were much lower than corresponding plasma concentrations, with a mean cefotaxime unbound brain-to-plasma area under the curve ratio equal to 26.1 ± 12.1%. This result was in accordance with the brain input-to-brain output clearances ratio (CL(in,brain)/CL(out,brain)). Unbound brain concentrations were then simulated at two dosing regimens (4 g every 6 h or 8 h), and the time over the MICs (T>MIC) was estimated for breakpoints of susceptible and resistant Streptococcus pneumoniae strains. T>MIC was higher than 90% of the dosing interval for both dosing regimens for susceptible strains and only for 4 g every 6 h for resistant ones. In conclusion, brain distribution of cefotaxime was well described by microdialysis in patients and was limited.

Pharmacokinetics of antibacterial agents in the CSF of children and adolescents

The adequate management of central nervous system (CNS) infections requires that antimicrobial agents penetrate the blood-brain barrier (BBB) and achieve concentrations in the CNS adequate for eradication of the infecting pathogen. This review details the currently available literature on the pharmacokinetics (PK) of antibacterials in the CNS of children. Clinical trials affirm that the physicochemical properties of a drug remain one of the most important factors dictating penetration of antimicrobial agents into the CNS, irrespective of the population being treated (i.e. small, lipophilic drugs with low protein binding exhibit the best translocation across the BBB). These same physicochemical characteristics determine the primary disposition pathways of the drug, and by extension the magnitude and duration of circulating drug concentrations in the plasma, a second major driving force behind achievable CNS drug concentrations. Notably, these disposition pathways can be expected to change during the normal process of growth and development. Finally, CNS drug penetration is influenced by the nature and extent of the infection (i.e. the presence of meningeal inflammation). Aminoglycosides have poor CNS penetration when administered intravenously. Intrathecal gentamicin has been studied in children with more promising results, often exceeding the minimum inhibitory concentration. There are very limited data with intrathecal tobramycin in children. However, in the few patients that have been studied, the CSF concentrations were highly variable. Penicillins generally have good CNS penetration. Aqueous penicillin G reaches greater concentrations than procaine or benzathine penicillin. Concentrations remain detectable for ≥ 12 h. Of the aminopenicillins, both ampicillin and parenteral amoxicillin reach adequate CNS concentrations; however, orally administered amoxicillin resulted in much lower concentrations. Nafcillin and piperacillin are the final two penicillins with pediatric data: their penetration is erratic at best. Cephalosporins vary greatly in regard to their CSF penetration. Few first- and second-generation cephalosporins are able to reach higher CSF concentrations. Cefuroxime is the only exception and is usually avoided due to its adverse effects and slower sterilization of the CSF than third-generation agents. Ceftriaxone, cefotaxime, ceftazidime, cefixime and cefepime have been studied in children and are all able to adequately penetrate the CSF. As with penicillins, concentrations are greatest in the presence of meningeal inflammation. Meropenem and imipenem are the only carbapenems with pediatric data. Imipenem reaches higher CSF concentrations; however, meropenem is preferred due to its lower incidence of seizures. Aztreonam has also demonstrated favorable penetration but only one study has been completed in children. Both chloramphenicol and sulfamethoxazole/trimethoprim (cotrimoxazole) penetrate into the CNS well; however, significant toxicities limit their use. The small size and minimal protein binding of fosfomycin contribute to its favorable CNS PK. Although rarely used, it achieves higher concentrations in the presence of inflammation and accumulation is possible. Linezolid reaches high CSF concentrations; however, more frequent dosing might be required in infants due to their increased elimination. Metronidazole also has very limited information but it demonstrated favorable results similar to adult data; CSF concentrations even exceeded plasma concentrations at certain time points. Rifampin (rifampicin) demonstrated good CNS penetration after oral administration. Vancomycin demonstrates poor CNS penetration after intravenous administration. When combined with intraventricular therapy, CNS concentrations are much greater. Of the antituberculosis agents, isoniazid, pyrazinamide and streptomycin have been studied in children. Isoniazid and pyrazinamide have favorable CSF penetration. Streptomycin appears to produce unpredictable CSF levels. No pediatric-specific data are available for clindamycin, daptomycin, macrolides, tetracyclines, and fluoroquinolones. Daptomycin, fluoroquinolones, and tetracyclines have demonstrated favorable CNS penetration in adults; however, data are limited due to their potential pediatric-specific toxicities and newness within the marketplace. Macrolides and clindamycin have demonstrated poor CNS penetration in adults and thus have not been studied in pediatrics.

Pharmacokinetics of doripenem in CSF of patients with non-inflamed meninges

OBJECTIVES

To investigate intact blood-brain barrier (BBB) penetration by doripenem and characterize doripenem pharmacokinetics in CSF using a pharmacokinetic model.

PATIENTS AND METHODS

Thirty-eight neurological patients with no active neurological disease or CNS infection received a single 500 mg doripenem dose before pump implantation surgery, or lumbar puncture, for intrathecal baclofen administration. In most cases single CSF and blood samples were collected per patient and analysed for doripenem with HPLC. A two-stage pharmacokinetic analysis was performed to estimate: (i) empirical Bayesian estimates (EBEs) of individual doripenem plasma pharmacokinetic parameters, using plasma doripenem concentrations and literature population priors for a two-compartment model; and (ii) doripenem CSF pharmacokinetic parameters using simulated plasma concentrations from stage (i) as a forcing function. The mean values of the structural model parameters, k(CSF) (distribution rate constant) and PC (CSF/plasma partition coefficient), and the residual variability were estimated.

RESULTS

The mean estimates of the parameters were k(CSF)= 0.105 h(-1) and PC= 0.053, corresponding to mean steady-state doripenem CSF concentrations of 0.20 mg/L and 0.40 mg/L for regimens of 3 × 500 mg daily and 3 × 1000 mg daily, respectively, and a mean equilibrium half-life of 6.6 h. The model was validated internally using a visual predictive check (VPC) and bootstrap. Simulating two dosing scenarios gave doripenem levels in the CSF above or close to the literature MIC values.

CONCLUSIONS

The present NONMEM software analysis shows that doripenem crosses intact BBB significantly and suggests that the drug should be further evaluated as a candidate to treat certain CNS infections, since drug penetration through BBB is enhanced by meningeal inflammation.

Adenosine and glutamate signaling in neuron-glial interactions: implications in alcoholism and sleep disorders

Recent studies have demonstrated that the function of glia is not restricted to the support of neuronal function. Especially, astrocytes are essential for neuronal activity in the brain. Astrocytes actively participate in synapse formation and brain information processing by releasing or uptaking gliotransmitters such as glutamate, d-serine, adenosine 5'-triphosphate (ATP), and adenosine. In the central nervous system, adenosine plays an important role in regulating neuronal activity as well as in controlling other neurotransmitter systems such as GABA, glutamate, and dopamine. Ethanol (EtOH) increases extracellular adenosine levels, which regulates the ataxic and hypnotic/sedative (somnogenic) effects of EtOH. Adenosine signaling is also involved in the homeostasis of major inhibitory/excitatory neurotransmission (i.e., GABA or glutamate) through neuron-glial interactions, which regulates the effect of EtOH and sleep. Adenosine transporters or astrocytic SNARE-mediated transmitter release regulates extracellular or synaptic adenosine levels. Adenosine then exerts its function through several adenosine receptors and regulates glutamate levels in the brain. This review presents novel findings on how neuron-glial interactions, particularly adenosinergic signaling and glutamate uptake activity involving glutamate transporter 1 (GLT1), are implicated in alcoholism and sleep disorders.

Environmental conditions modulate neurotoxic effects of psychomotor stimulant drugs of abuse

Psychomotor stimulants such as methamphetamine (METH), amphetamine, and 3,4-metylenedioxymethamphetamine (MDMA or ecstasy) are potent addictive drugs. While it is known that their abuse could result in adverse health complications, including neurotoxicity, both the environmental conditions and activity states associated with their intake could strongly enhance drug toxicity, often resulting in life-threatening health complications. In this review, we analyze results of animal experiments that suggest that even moderate increases in environmental temperatures and physiological activation, the conditions typical of human raves parties, dramatically potentiate brain hyperthermic effects of METH and MDMA. We demonstrate that METH also induces breakdown of the blood-brain barrier, acute glial activation, brain edema, and structural abnormalities of various subtypes of brain cells; these effects are also strongly enhanced when the drug is used at moderately warm environmental conditions. We consider the mechanisms underlying environmental modulation of acute drug neurotoxicity and focus on the role of brain temperature, a critical homeostatic parameter that could be affected by metabolism-enhancing drugs and environmental conditions and affect neural activity and functions.

Penetration of drugs through the blood-cerebrospinal fluid/blood-brain barrier for treatment of central nervous system infections

The entry of anti-infectives into the central nervous system (CNS) depends on the compartment studied, molecular size, electric charge, lipophilicity, plasma protein binding, affinity to active transport systems at the blood-brain/blood-cerebrospinal fluid (CSF) barrier, and host factors such as meningeal inflammation and CSF flow. Since concentrations in microdialysates and abscesses are not frequently available for humans, this review focuses on drug CSF concentrations. The ideal compound to treat CNS infections is of small molecular size, is moderately lipophilic, has a low level of plasma protein binding, has a volume of distribution of around 1 liter/kg, and is not a strong ligand of an efflux pump at the blood-brain or blood-CSF barrier. When several equally active compounds are available, a drug which comes close to these physicochemical and pharmacokinetic properties should be preferred. Several anti-infectives (e.g., isoniazid, pyrazinamide, linezolid, metronidazole, fluconazole, and some fluoroquinolones) reach a CSF-to-serum ratio of the areas under the curves close to 1.0 and, therefore, are extremely valuable for the treatment of CNS infections. In many cases, however, pharmacokinetics have to be balanced against in vitro activity. Direct injection of drugs, which do not readily penetrate into the CNS, into the ventricular or lumbar CSF is indicated when other effective therapeutic options are unavailable.

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.

Survey of prophylactic antibiotic use amongst UK cochlear implant surgeons

Cochlear implant patients are at an increased risk of pneumococcal meningitis. Recent government guidelines require all implant patients to undergo pneumococcal vaccination. The guidelines also suggest antibiotic prophylaxis but no clear guidelines regarding which antibiotic to use or for how long were issued.We asked each implant centre within the UK to describe their antibiotic protocol for cochlear implantation.Our results have showed that 100% of UK implant surgeons use antibiotic prophylaxis. The type of antibiotic and duration vary significantly between centres. Interestingly, however, the regimes followed by most practices do not adhere to surgical principles of antibiotic prophylaxis.

Protein binding of antimicrobials: methods for quantification and for investigation of its impact on bacterial killing

Plasma protein binding of antimicrobial agents is considered to be a key characteristic of antibiotics as it affects both their pharmacokinetics and pharmacodynamics. However, up to the present, no standard methods for measuring protein binding or for quantification of the influence of protein binding on antimicrobial activity exist. This short-coming has previously led to conflicting results on antibacterial activity of highly protein-bound antibiotics. The present review, therefore, set out to summarize (1) methods for quantification of protein binding, (2) microbiological growth media used for determination of the impact of protein binding on antimicrobial activity of antibiotics, and (3) different pharmacodynamic in vitro studies that are used in this context. The advantages and disadvantages of a wide range of different approaches are discussed and compared. The urgent call for international standardization by microbiological societies and laboratories may be considered as a logical consequence of the presented data.

Antimicrobial activity of cefepime and rifampicin in cerebrospinal fluid in vitro

OBJECTIVES

Though used for infections of the central nervous system, the pharmacodynamics of antimicrobial agents is commonly evaluated only in commercially available bacterial growth media. In the present study, the effects of cerebrospinal fluid (CSF) on bacterial killing by cefepime and rifampicin were investigated.

METHODS

CSF was collected from patients who did not receive antibiotics. Time-kill curves were performed over 24 h using drug concentrations of 0.25-, 0.5-, 1-, 2-, 4- and 8-fold the respective MIC for the Staphylococcus aureus test strain. Killing curves were performed in Mueller-Hinton broth (MHB), in CSF incubated in ambient air (CSF(AIR)) and in CSF in air with 5% CO(2) (CSF(CO(2))). CO(2) served to adjust the pH of CSF to physiological values.

RESULTS

Sustained bacterial killing was achieved by cefepime at lower drug concentrations in CSF(CO(2)) than in MHB. In contrast, rifampicin concentrations above the MIC were required to exert sustained killing in CSF(CO(2)). Both drugs were least effective in CSF(AIR).

CONCLUSIONS

Standard susceptibility tests may lead to over- or underestimation of the activity of distinct antibiotics in CSF. Evaluation of the antimicrobial activity in pH-adjusted CSF can provide useful information on drugs considered for the treatment of bacterial infections residing in CSF.

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.

Pharmacokinetics of cefovecin in cats

The pharmacokinetics of the novel cephalosporin cefovecin were investigated in a series of in vivo, ex vivo and in vitro studies following administration to adult cats at 8 mg/kg bodyweight. Bioavailability and pharmacokinetic parameters were determined in a cross-over study after intravenous (i.v.) and subcutaneous (s.c.) injections. [14C]cefovecin was used to evaluate excretion for 21 days after s.c. administration. Protein binding was determined in vitro in feline plasma and ex vivo in transudate from cats surgically implanted with tissue chambers. After s.c. administration, cefovecin was characterized by rapid absorption with mean peak plasma concentrations of 141+/-12 microg/mL being achieved within 2 h of s.c. injection with full bioavailability (99%). The mean elimination half-life was 166+/-18 h. After i.v. administration, volume of distribution was 0.09+/-0.01 L/kg and mean plasma clearance was 0.35+/-0.04 mL/h/kg. Approximately 50% of the administered radiolabelled dose was eliminated over the 21-day postdose period via urinary excretion and up to approximately 25% in faeces. In vitro and ex vivo plasma protein binding ranged from 99.8% to 99.5% over the plasma concentration range 10-100 microg/mL. Ex vivo protein binding in transudate was as low as 90.7%. From 8 h postdose, concentrations of unbound (free) cefovecin in transudate were consistently higher than in plasma, with mean unbound cefovecin concentrations being maintained above 0.06 microg/mL (MIC90 of Pasteurella multocida) in transudate for at least 14 days postdose. The slow elimination and long-lasting free concentrations in extracellular fluid are desirable pharmacokinetic attributes for an antimicrobial with a 14-day dosing interval.

Pharmacodynamic evaluation of meropenem and cefotaxime for pediatric meningitis: a report from the OPTAMA program

OBJECTIVE

To determine the probability of meropenem (Merrem, AstraZeneca Pharmaceuticals L.P., Wilmington, DE, USA) and cefotaxime (Claforan, Aventis Pharmaceuticals Inc., Bridgewater, NJ, USA) achieving bactericidal exposures in the cerebrospinal fluid against Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae.

METHODS

A 5,000-patient Monte Carlo simulation in a population of 10-year-old children with meningitis was conducted. Pediatric pharmacokinetic data were derived from the literature. Pathogen minimum inhibitory concentrations (MICs) were obtained from common bacteria that had caused meningitis collected during pediatric clinical trials. Time above the MIC exposures in the cerebrospinal fluid was calculated. Bactericidal exposure or probability of target attainment was defined as 40% and 50% time above the MIC for meropenem and cefotaxime, respectively. High cumulative fractions of responses were defined as >90% probability of target attainment against the populations of bacteria.

RESULTS

Meropenem was calculated to achieve 94.7%, 94.3%, and 96.1% cumulative fractions of response against S. pneumoniae, H. influenzae, and N. meningitidis, respectively. Cefotaxime only achieved a high likelihood of bactericidal attainment against N. meningitidis (91.6%). Against S. pneumoniae and H. influenzae, cefotaxime was only calculated to achieve 84.3% and 84.8% cumulative fractions of response, respectively.

CONCLUSION

In a simulated population of 10-year-old children, meropenem had a high likelihood of attaining bactericidal exposures in the cerebrospinal fluid. Cefotaxime had a >90% cumulative fraction of response against only N. meningitidis. Therefore, at the doses simulated, meropenem may be a more appropriate empiric choice for the treatment of bacterial meningitis in pediatric patients presumed to be caused by these pathogens until culture and susceptibility data are available.

PEPT2 (Slc15a2)-Mediated Unidirectional Transport of Cefadroxil from Cerebrospinal Fluid into Choroid Plexus

Cefadroxil is a cephalosporin antibiotic used in the treatment of infection. However, cerebrospinal fluid (CSF) concentrations of cefadroxil and other aminocephalosporins are not adequate for the treatment of bacterial meningitis. To evaluate the relevance of PEPT2 in affecting the exposure of aminocephalosporins in brain, we investigated the transport properties of cefadroxil at the blood-CSF interface using primary-cultured epithelial cells and isolated whole tissues of choroid plexus. Our results indicated that cefadroxil was preferentially taken up from the apical as opposed to basal side of the monolayer (5-fold), and its apical uptake was stimulated by an inwardly directed proton gradient. The concentration-dependent apical uptake of cefadroxil was characterized by a high-affinity/low-capacity transport system (Km = 39.0 +/- 22.7 microM; Vmax = 22.9 +/- 6.6 pmol/mg/min) and a nonsaturable component (Kd = 0.15 +/- 0.01 microl/mg/min); in contrast, only a nonsaturable component was found for the basal uptake of cefadroxil (Kd = 0.14 +/- 0.01 microl/mg/min). The apical-to-basal transepithelial transport of 2 microM cefadroxil was greater than its basal-to-apical transport, but no differences were observed in directionality when 5 mM concentrations of cefadroxil were studied. Moreover, the cellular efflux of cefadroxil was not saturable in either direction (i.e., to apical or basal side). Finally, no differences were observed in the choroid plexus tissue efflux of 2 microM cefadroxil from wild-type and PEPT2 null mice. These findings demonstrate that PEPT2 has an important role in limiting the exposure of cefadroxil in CSF. Located at the apical membrane of choroid plexus epithelium, PEPT2 acts in a unidirectional (as opposed to bidirectional) manner in transporting cefadroxil from CSF into the cell.

Disposition of cefepime in the central nervous system of patients with external ventricular drains

STUDY OBJECTIVE

To assess central nervous system (CNS) penetration of cefepime in adults with external ventricular drains and to compare the achieved cerebrospinal fluid (CSF) concentrations with the usual minimum inhibitory concentrations (MICs) of common pathogens.

DESIGN

Open-label, prospective study.

SETTING

University-affiliated medical center.

PATIENTS

Seven patients with external ventricular drains and normal renal function (documented creatinine clearance > 60 ml/min) who received cefepime 2 g intravenously every 12 hours for treatment of nosocomial pneumonia.

INTERVENTION

Serial serum and CSF samples were obtained concurrently after the fourth dose during one dosing interval.

MEASUREMENTS AND MAIN RESULTS

The concentration-time profiles in serum and CSF were comodeled by using a two-compartment model with zero-order infusion to the central compartment. The CSF concentration-time profiles of the individual patients were compared with published MIC90 of common pathogens isolated in nosocomial meningitis. Our model reasonably characterized the disposition of cefepime in serum and CSF. Penetration into the CNS was 4-34% based on area under the curve and was 5-58% based on minimum concentration.

CONCLUSION

Penetration of cefepime into the CNS was variable among the patients (4-34%) but appeared similar to that reported for other cephalosporins given to treat meningitis. The concentrations attained by most patients in this study were above the MIC90 of many common nosocomial organisms.

Retrospective review of neurotoxicity induced by cefepime and ceftazidime

We reviewed 42 cases of cefepime-induced neurotoxicity and 12 cases of ceftazidime-induced neurotoxicity from the literature and our institution. Clinical characteristics and timing of diagnosis were examined. Common findings were confusion with temporospatial disorientation (96% of patients), myoclonus (33%), and seizures (13%). These neurologic disorders frequently are encountered in uremic and elderly patients, who often are in a confused state when they visit their physician. The risk of delayed diagnosis was greater with cefepime than ceftazidime neurotoxicity. The median interval between symptom onset and diagnosis of cefepime versus ceftazidime neurotoxicity was 5 and 3 days, respectively (p=0.005). Delayed diagnosis of cefepime neurotoxicity may be due to lack of awareness of the adverse effect. Data gathered since these two broad-spectrum antibiotics were first marketed underscore the potential for neurologic adverse events secondary to their administration. Thus, clinicians' awareness must be increased so that the time between symptom onset and diagnosis can be reduced.