Electrically Driven Hyperbolic Nanophotonic Resonators as High Speed, Spectrally Selective Thermal Radiators

We introduce and experimentally demonstrate electrically driven, spectrally selective thermal emitters based on globally aligned carbon nanotube metamaterials. The self-assembled metamaterial supports a high degree of nanotube ordering, enabling nanoscale ribbons patterned in the metamaterial to function both as Joule-heated incandescent filaments and as infrared hyperbolic resonators imparting spectral selectivity to the thermal radiation. Devices batch-fabricated on a single chip emit polarized thermal radiation with peak wavelengths dictated by their hyperbolic resonances, and their nanoscale heated dimensions yield modulation rates as high as 1 MHz. As a proof of concept, we show that two sets of thermal emitters on the same chip, operating with different peak wavelengths and modulation rates, can be used to sense carbon dioxide with one detector. We anticipate that the combination of batch fabrication, modulation bandwidth, and spectral tuning with chip-based nanotube thermal emitters will enable new modalities in multiplexed infrared sources.

Prospective Study of Policies and Use of Therapies for COVID-19 Amongst Australian Health Services during 2020

BACKGROUND

The COVID-19 pandemic has generated significant debate about how emerging infections can be treated in the absence of evidence-based therapies to combat disease. In particular, the use of off-label therapies outside of a clinical trial setting has been controversial.

AIM

We aimed to longitudinally study policies and prescribing practices pertaining to therapies for COVID-19 in Australian Health Services in 2020.

METHODS

Prospective data was collected from participating Australian health services who may care for patients with COVID-19 via an electronic portal. A single informant from each health service was emailed a survey link at regular intervals. Information was sought regarding changes to COVID-19 policy at their service and use of therapies for COVID-19.

RESULTS

Overall, 78 hospitals were represented from 39 respondents with longitudinal data collection from May to December 2020. All Australian states/territories were represented with the majority of respondents located in a major city (34/39; 87%). Just over half (20/39) of respondents had a written policy for COVID-19 therapy use at their health service at survey enrolment and policies changed frequently throughout the pandemic. Therapy use outside of a clinical trial was reported in 54% of health services, most frequently in Victoria, correlating with higher numbers of COVID-19 cases. At study commencement hydroxychloroquine was most frequently used, with corticosteroids and remdesivir use increasingly throughout the study period.

CONCLUSION

Our results reflect the reactive nature of prescribing of therapies for COVID-19 and highlight the importance of evidence-based guidelines to assist prescribers. This article is protected by copyright. All rights reserved.

Non-polymyxin-based combinations as potential alternatives in treatment against carbapenem-resistant Acinetobacter baumannii infections

Due to limited therapeutic options, combination therapy has been used empirically to treat carbapenem-resistant Acinetobacter baumannii (CRAB). Polymyxin-based combinations have been widely studied and used in the clinical setting. However, the use of polymyxins is often limited due to nephrotoxicity and neurotoxicity. This study aimed to evaluate the activity of non-polymyxin-based combinations relative to polymyxin-based combinations and to identify potential synergistic and bactericidal two-drug non-polymyxin-based combinations against CRAB. In vitro activity of 14 two-drug combinations against 50 A. baumannii isolates was evaluated using the checkerboard method. Subsequently, the two best-performing non-polymyxin-based combinations from the checkerboard assay were explored in static time-kill experiments. Concentrations of antibiotics corresponding to the fractional inhibitory concentrations (FIC) and the highest serum concentration achievable clinically were tested. The most synergistic combinations were fosfomycin/sulbactam (synergistic against 37/50 isolates; 74%), followed by meropenem/sulbactam (synergistic against 28/50 isolates; 56%). No antagonism was observed for any combination. Both fosfomycin/sulbactam and meropenem/sulbactam combinations exhibited bactericidal and synergistic activity against both isolates at the highest clinically achievable concentrations in the time-kill experiments. The meropenem/sulbactam combination displayed synergistic and bactericidal activity against one of two strains at concentrations equal to the FIC. Non-polymyxin-based combinations such as fosfomycin/sulbactam and meropenem/sulbactam may have a role in the treatment of CRAB. Further in vivo and clinical studies are required to scrutinise these activities further.

How to design a study to evaluate therapeutic drug monitoring in infectious diseases?

BACKGROUND

Therapeutic drug monitoring (TDM) is a tool to personalize and optimize dosing by measuring the drug concentration and subsequently adjusting the dose to reach a target concentration or exposure. The evidence to support TDM is however often ranked as expert opinion. Limitations in study design and sample size have hampered definitive conclusions of the potential added value of TDM.

OBJECTIVES

We aim to give expert opinion and discuss the main points and limitations of available data from antibiotic TDM trials and emphasize key elements for consideration in design of future clinical studies to quantify the benefits of TDM.

SOURCES

The sources were peer-reviewed publications, guidelines and expert opinions from the field of TDM.

CONTENT

This review focuses on key aspects of antimicrobial TDM study design: describing the rationale for a TDM study, assessing the exposure of a drug, assessing susceptibility of pathogens and selecting appropriate clinical endpoints. Moreover we provide guidance on appropriate study design.

IMPLICATIONS

This is an overview of different aspects relevant for the conduct of a TDM study. We believe that this paper will help researchers and clinicians to design and conduct high-quality TDM studies.

Reducing post-caesarean delivery surgical site infections: a narrative review

Surgical site infection complicates 1-10% of caesarean deliveries. With the rate of caesarean delivery increasing, it is important to identify effective measures of preventing surgical site infection and to consider their impact on maternal and neonatal outcomes. Compelling evidence supports the use of prophylactic antibiotics, prior to skin incision, to reduce surgical site infection. However, there remain international variations in terms of the recommended agent, dose and body weight-adjusted dosing. Advances in wound dressings are an evolving area of interest and surgical technique can influence outcomes. This narrative review explores pharmacological and non-pharmacological methods of preventing surgical site infection following caesarean delivery.

Saturable elimination of piperacillin in critically ill patients: implications for continuous infusion

The study aimed to evaluate saturation of piperacillin elimination in critically ill adult patients. Seventeen critically ill adult patients received continuous and intermittent infusion of piperacillin/tazobactam. Piperacillin plasma concentrations (n = 217) were analysed using population pharmacokinetic (PopPK) modelling. Post-hoc simulations were performed to evaluate the type I error rate associated with the study. Unseen data were used to validate the final model. The mean error (ME) and root mean square error (RMSE) were calculated as a measure of bias and imprecision, respectively. A PopPK model with parallel linear and non-linear elimination best fitted the data. The median and 95% confidence interval (CI) for the model parameters drug clearance (CL), volume of central compartment (V), volume of peripheral compartment (V_p) and intercompartmental clearance (Q) were 9 (7.69-11) L/h, 6.18 (4.93-11.2) L, 11.17 (7.26-12) L and 15.61 (12.66-23.8) L/h, respectively. The Michaelis-Menten constant (K_m) and the maximum elimination rate for Michaelis-Menten elimination (V_max) were estimated without population variability in the model to avoid overfitting and inflation of the type I error rate. The population estimates for K_m and V_max were 37.09 mg/L and 353.57 mg/h, respectively. The bias (ME) was -20.8 (95% CI -26.2 to -15.4) mg/L, whilst imprecision (RMSE) was 49.2 (95% CI 41.2-56) mg/L. In conclusion, piperacillin elimination is (partially) saturable. Moreover, the population estimate for K_m lies within the therapeutic window and therefore saturation of elimination should be accounted for when defining optimum dosing regimens for piperacillin in critically ill patients.

Tunable Hyperbolic Metamaterials Based on Self-Assembled Carbon Nanotubes

We show that packed, horizontally aligned films of single-walled carbon nanotubes are hyperbolic metamaterials with ultrasubwavelength unit cells and dynamic tunability. Using Mueller matrix ellipsometry, we characterize the films' optical properties, which are doping level dependent, and find a broadband hyperbolic region tunable in the mid-infrared. To characterize the dispersion of in-plane hyperbolic plasmon modes, we etch the nanotube films into nanoribbons with differing widths and orientations relative to the nanotube axis, and we observe that the hyperbolic modes support strong light localization. An agreement between the experiments and theoretical models using the ellipsometry data indicates that the packed carbon nanotubes support bulk anisotropic responses at the nanoscale. Self-assembled films of carbon nanotubes are well-suited for applications in thermal emission and photodetection, and they serve as model systems for studying light-matter interactions in the deep subwavelength regime.

Individualising Therapy to Minimize Bacterial Multidrug Resistance

The scourge of antibiotic resistance threatens modern healthcare delivery. A contributing factor to this significant issue may be antibiotic dosing, whereby standard antibiotic regimens are unable to suppress the emergence of antibiotic resistance. This article aims to review the role of pharmacokinetic and pharmacodynamic (PK/PD) measures for optimising antibiotic therapy to minimise resistance emergence. It also seeks to describe the utility of combination antibiotic therapy for suppression of resistance and summarise the role of biomarkers in individualising antibiotic therapy. Scientific journals indexed in PubMed and Web of Science were searched to identify relevant articles and summarise existing evidence. Studies suggest that optimising antibiotic dosing to attain defined PK/PD ratios may limit the emergence of resistance. A maximum aminoglycoside concentration to minimum inhibitory concentration (MIC) ratio of > 20, a fluoroquinolone area under the concentration-time curve to MIC ratio of > 285 and a β-lactam trough concentration of > 6 × MIC are likely required for resistance suppression. In vitro studies demonstrate a clear advantage for some antibiotic combinations. However, clinical evidence is limited, suggesting that the use of combination regimens should be assessed on an individual patient basis. Biomarkers, such as procalcitonin, may help to individualise and reduce the duration of antibiotic treatment, which may minimise antibiotic resistance emergence during therapy. Future studies should translate laboratory-based studies into clinical trials and validate the appropriate clinical PK/PD predictors required for resistance suppression in vivo. Other adjunct strategies, such as biomarker-guided therapy or the use of antibiotic combinations require further investigation.

Comparative total and unbound pharmacokinetics of cefazolin administered by bolus versus continuous infusion in patients undergoing major surgery: a randomized controlled trial

Background.

Perioperative administration of cefazolin reduces the incidence of perioperative infections. Intraoperative re-dosing of cefazolin is commonly given between 2 and 5 h after the initial dose. This study was undertaken to determine whether intraoperative continuous infusions of cefazolin achieve better probability of target attainment (PTA) and fractional target attainment (FTA) than intermittent dosing.

Methods.

Patients undergoing major surgery received cefazolin 2 g before surgical incision. They were subsequently randomized to receive either an intermittent bolus (2 g every 4 h) or continuous infusion (500 mg h -1 ) of cefazolin until skin closure. Blood samples were analysed for total and unbound cefazolin concentrations using a validated chromatographic method. Population pharmacokinetic modelling was performed using Pmetrics ® software. Calculations of PTA and FTA were performed for common pathogens.

Results.

Ten patients were enrolled in each arm. A two-compartment linear model best described the time course of the total plasma cefazolin concentrations. The covariates that improved the model were body weight and creatinine clearance. Protein binding varied with time [mean (range) 69 (44-80)%] with a fixed 21% unbound value of cefazolin used for the simulations (120 min post-initial dosing). Mean ( sd ) central volume of distribution was 5.73 (2.42) litres, and total cefazolin clearance was 4.72 (1.1) litres h -1 . Continuous infusions of cefazolin consistently achieved better drug exposures and FTA for different weight and creatinine clearances, particularly for less susceptible pathogens.

Conclusions.

Our study demonstrates that intraoperative continuous infusions of cefazolin increase the achievement of target plasma concentrations, even with lower infusion doses. Renal function and body weight are important when considering the need for alternative dosing regimens.

Clinical trial registration.

NCT02058979.

Optimised dosing of vancomycin in critically ill Indigenous Australian patients with severe sepsis

Vancomycin is a commonly used antibiotic due to the high burden of methicillin-resistant <i>Staphylococcus aureus</i> infections. This study aimed to describe the pharmacokinetics (PK) of vancomycin in Australian Indigenous patients with severe sepsis, and advise an optimal dosing strategy. A population PK study was conducted in a remote Australian intensive care unit (ICU). Serial plasma samples were collected over one to two dosing intervals and assayed by validated chromatography. Concentration-time data collected were analysed using Pmetrics® software. The final population PK model was then used for Monte Carlo dosing simulations to determine optimal loading and intermittent maintenance doses. Fifteen Indigenous subjects were included for analysis with a median (interquartile range, IQR) age, weight and creatinine clearance (CrCL) of 43 (34-46) years, 73 (66-104) kg and 99 (56-139) ml/minute respectively. A two-compartment model described the data adequately. Vancomycin clearance (CL) and volume of distribution of the central compartment (Vc) were described by CrCL and patient weight respectively. Median (IQR) CL, Vc, distribution rate constants from central to peripheral, and from peripheral to central compartments were 4.6 (3.8-5.6) litres per hour, 25.4 (16.1-31.3) litres, 0.46 (0.28-0.52)/hour and 0.25 (0.12-0.37)/hour respectively. No significant interethnic PK differences were observed in comparison to published data. Therapeutic loading doses were significantly dependent on both weight and CrCL, whereas maintenance doses were dependent on CrCL. In the absence of severe renal impairment, initiation of maintenance dose eight hours post-loading dose achieved higher probability of target attainment at 24 hours. This is the first report of vancomycin PK in this patient group.

Gut-derived serotonin contributes to bone deficits in colitis

Osteoporosis and bone fractures occur at higher frequency in patients with inflammatory bowel disease (IBD), and decreased bone mass is observed in animal models of colitis. Another consistent feature of colitis is increased serotonin (5-HT) availability in the intestinal mucosa. Since gut-derived 5-HT can decrease bone mass, via activation of 5-HT_1B receptors on pre-osteoblasts, we tested the hypothesis that 5-HT contributes to bone loss in colitis. Colitis was chronically induced in mice by adding dextran sodium sulfate (DSS) to their drinking water for 21 days. At day 21, circulating 5-HT levels were elevated in DSS-inflamed mice. Micro-computed tomography of femurs showed a decrease in trabecular bone volume fraction, formation, and surface area, due largely to decreased trabecular numbers in DSS-treated mice. The colitis-induced loss of trabecular bone was significantly suppressed in mice treated with the 5-HT synthesis inhibitor, p-chloro-DL-phenylalanine (PCPA; 300 mg/kg/day IP daily), and in mice treated with the 5-HT_1B receptor antagonist GR55562 (1 mg/Kg/day SC daily). The 5-HT reuptake transporter (SERT) is critical for moving 5-HT from the interstitial space into enterocytes and from serum into platelets. Mice lacking SERT exhibited significant deficits in trabecular bone mass that are similar to those observed in DSS-inflamed mice, and these deficits were not extensively worsened by DSS-induced colitis in the SERT-/- mice. Taken together, findings from both the DSS and SERT-/- mouse models support a contributing role for 5-HT as a significant factor in bone loss induced by colitis.

Prevalence of augmented renal clearance and performance of glomerular filtration estimates in Indigenous Australian patients requiring intensive care admission

Augmented renal clearance (ARC) refers to the enhanced renal excretion of circulating solute commonly demonstrated in numerous critically ill subgroups. This study aimed to describe the prevalence of ARC in critically ill Indigenous Australian patients and explore the accuracy of commonly employed mathematical estimates of glomerular filtration. We completed a single-centre, prospective, observational study in the intensive care unit (ICU), Alice Springs Hospital, Central Australia. Participants were critically ill adult Indigenous and non-Indigenous Australian patients with a urinary catheter in situ. Exclusion criteria were anuria, pregnancy or the requirement for renal replacement therapy. Daily eight-hour measured creatinine clearances (CrCL_m) were collected throughout the ICU stay. ARC was defined by a CrCL_m ≥130 ml/min/1.73 m². The Cockcroft-Gault and Chronic Kidney Disease Epidemiology Collaboration equations were also used to calculate mathematical estimates for comparison. In total, 131 patients were recruited (97 Indigenous, 34 non-Indigenous) and 445 samples were collected. The median (range) CrCL_m was 93.0 (5.14 to 205.2) and 90.4 (18.7 to 206.8) ml/min/1.73 m² in Indigenous and non-Indigenous patients, respectively. Thirty-one of 97 (32%) Indigenous patients manifested ARC, compared to 7 of 34 (21%) non-Indigenous patients (<i>P</i>=0.21). Younger age, major surgery, higher baseline renal function and an absence of diabetes were all associated with ARC. Both mathematical estimates manifest limited accuracy. ARC was prevalent in critically ill Indigenous patients, which places them at significant risk of underdosing with renally excreted drugs. CrCL_m should be obtained wherever possible to ensure accurate dosing.

Delivering precision antimicrobial therapy through closed-loop control systems

Sub-optimal exposure to antimicrobial therapy is associated with poor patient outcomes and the development of antimicrobial resistance. Mechanisms for optimizing the concentration of a drug within the individual patient are under development. However, several barriers remain in realizing true individualization of therapy. These include problems with plasma drug sampling, availability of appropriate assays, and current mechanisms for dose adjustment. Biosensor technology offers a means of providing real-time monitoring of antimicrobials in a minimally invasive fashion. We report the potential for using microneedle biosensor technology as part of closed-loop control systems for the optimization of antimicrobial therapy in individual patients.

Use of nebulized antimicrobials for the treatment of respiratory infections in invasively mechanically ventilated adults: a position paper from the European Society of Clinical Microbiology and Infectious Diseases

With an established role in cystic fibrosis and bronchiectasis, nebulized antibiotics are increasingly being used to treat respiratory infections in critically ill invasively mechanically ventilated adult patients. Although there is limited evidence describing their efficacy and safety, in an era when there is a need for new strategies to enhance antibiotic effectiveness because of a shortage of new agents and increases in antibiotic resistance, the potential of nebulization of antibiotics to optimize therapy is considered of high interest, particularly in patients infected with multidrug-resistant pathogens. This Position Paper of the European Society of Clinical Microbiology and Infectious Diseases provides recommendations based on the Grading of Recommendations Assessment, Development and Evaluation (GRADE) methodology regarding the use of nebulized antibiotics in invasively mechanically ventilated adults, based on a systematic review and meta-analysis of the existing literature (last search July 2016). Overall, the panel recommends avoiding the use of nebulized antibiotics in clinical practice, due to a weak level of evidence of their efficacy and the high potential for underestimated risks of adverse events (particularly, respiratory complications). Higher-quality evidence is urgently needed to inform clinical practice. Priorities of future research are detailed in the second part of the Position Paper as guidance for researchers in this field. In particular, the panel identified an urgent need for randomized clinical trials of nebulized antibiotic therapy as part of a substitution approach to treatment of pneumonia due to multidrug-resistant pathogens.

Key considerations on nebulization of antimicrobial agents to mechanically ventilated patients

Nebulized antibiotics have an established role in patients with cystic fibrosis or bronchiectasis. Their potential benefit to treat respiratory infections in mechanically ventilated patients is receiving increasing interest. In this consensus statement of the European Society of Clinical Microbiology and Infectious Diseases, the body of evidence of the therapeutic utility of aerosolized antibiotics in mechanically ventilated patients was reviewed and resulted in the following recommendations: Vibrating-mesh nebulizers should be preferred to jet or ultrasonic nebulizers. To decrease turbulence and limit circuit and tracheobronchial deposition, we recommend: (a) the use of specifically designed respiratory circuits avoiding sharp angles and characterized by smooth inner surfaces, (b) the use of specific ventilator settings during nebulization including use of a volume controlled mode using constant inspiratory flow, tidal volume 8 mL/kg, respiratory frequency 12 to 15 bpm, inspiratory:expiratory ratio 50%, inspiratory pause 20% and positive end-expiratory pressure 5 to 10 cm H₂O and (c) the administration of a short-acting sedative agent if coordination between the patient and the ventilator is not obtained, to avoid patient's flow triggering and episodes of peak decelerating inspiratory flow. A filter should be inserted on the expiratory limb to protect the ventilator flow device and changed between each nebulization to avoid expiratory flow obstruction. A heat and moisture exchanger and/or conventional heated humidifier should be stopped during the nebulization period to avoid a massive loss of aerosolized particles through trapping and condensation. If these technical requirements are not followed, there is a high risk of treatment failure and adverse events in mechanically ventilated patients receiving nebulized antibiotics for pneumonia.

The effect of pharmacists on ward rounds measured by the STOPP/START tool in a specialized geriatric unit

WHAT IS KNOWN AND OBJECTIVE

The STOPP/START tool has been validated to assess elderly patients for potentially inappropriate prescribing. This study aimed to assess the effect of inclusion of a pharmacist on a physician-led ward round on potentially inappropriate prescribing in hospitalized elderly patients.

METHODS

This was an observational study of prescribing for patients using the STOPP/START tool at three points during hospital stay; admission to hospital, on transfer to the specialized geriatric unit and on discharge from hospital. Data were collected over 4 months pre- and post-introduction of a pharmacist to a physician-led ward round. Demographic and clinical data, including total number of medications and STOPP/START criteria met, were collected. The mean number of STOPP/START criteria at each time-point was compared for pre- and post-introduction of a pharmacist using a Mann-Whitney U-test. The mean number of criteria for each time-point within each group was compared using a paired Student's t-test.

RESULTS AND DISCUSSION

The demographic characteristics of the participants in the pre- and post-intervention groups were similar. The post-intervention group had numerically less STOPP/START criteria, mean 1·18 (1·37) compared to the pre-intervention group 1·50 (1·41), P = 0·07 at discharge. The pre-intervention group had no significant change in the criteria from admission 1·78 (1·57) to geriatric unit transfer 1·72 (1·54) (P = 0·37); however, there was a significant decrease from geriatric unit transfer 1·72 (1·54) to discharge 1·50 (1·41) (P = 0·02). The post-intervention group had a significant decrease from hospital admission 2·30 (1·91) to geriatric unit transfer 1·59 (1·60) (P < 0·01) and again to discharge 1·18 (1·37) (P < 0·01).

WHAT IS NEW AND CONCLUSION

Pharmacist participation on the ward round in a specialized geriatric unit resulted in a numerical improvement in prescribing quality as measured by the STOPP/START tool.

A continent-wide analysis of the shade requirements of red and western grey kangaroos

Foraging time may be constrained by a suite of phenomena including weather, which can restrict a species' activity and energy intake. This is recognized as pivotal for many species whose distributions are known to correlate with climate, including kangaroos, although such impacts are rarely quantified. We explore how differences in shade seeking, a thermoregulatory behavior, of 2 closely-related kangaroo species, Macropus rufus (red kangaroos) and M. fuliginosus (western grey kangaroos), might reflect differences in their distributions across Australia. We observed foraging and shade-seeking behavior in the field and, together with local weather observations, calculated threshold radiant temperatures (based on solar and infrared radiant heat loads) over which the kangaroos retreated to shade. We apply these calculated tolerance thresholds to hourly microclimatic estimates derived from daily-gridded weather data to predict activity constraints across the Australian continent over a 10-year period. M. fuliginosus spent more time than M. rufus in the shade (7.6 ± 0.7 h versus 6.4 ± 0.9 h) and more time foraging (11.8 ± 0.5 h vs. 10.0 ± 0.6 h), although total time resting was equivalent (∼8.2 h). M. rufus tolerated 19°C higher radiant temperatures than M. fuliginosus (89°C versus 70°C radiant temperature). Across Australia, we predicted M. fuliginosus to be more restricted to shade than M. rufus, with higher absolute shade requirements farther north. These results corroborate previous findings that M. rufus is more adept at dealing with heat than M. fuliginosus and indicate that M. rufus is less dependent on shade on a continental scale.

Integrated pharmacokinetic-pharmacodynamic modelling to evaluate antimicrobial prophylaxis in abdominal surgery

OBJECTIVES

To use Monte Carlo simulation with an integrated pharmacokinetic-pharmacodynamic (PK-PD) model to evaluate guideline-recommended antimicrobial prophylaxis (AP) regimens with anaerobic coverage in abdominal surgery.

METHODS

AP regimens were tested in simulated subjects undergoing elective abdominal surgery using relevant PK models and pathogen distributions in surgical site infections (SSIs). Predicted cumulative target attainment was the percentage of simulated subjects with free (unbound) antimicrobial plasma concentrations above the MICs for potential SSI pathogens.

RESULTS

Cefazolin plus metronidazole covered SSI aerobes in 70% and the Bacteroides fragilis group in 99% of subjects, whereas cefoxitin only covered aerobes and anaerobes in 63% and 27% of cases, respectively. The broad-spectrum ceftriaxone plus metronidazole covered aerobes in 82% and anaerobes in 99% of simulations, while ertapenem covered aerobes in 88% and anaerobes in 90% of cases. Clindamycin covered the B. fragilis group in only 11% of cases. For cefazolin, 2 g doses maintained target attainment in simulated subjects from 80 to 120 kg, whereas 1 g doses were associated with lower target attainment against potential Gram-negative pathogens even in those <80 kg. For gentamicin, 3 mg/kg doses were comparable to the suggested 5 mg/kg, but superior to the traditional 1.5 mg/kg.

CONCLUSIONS

This study demonstrates the use of PK-PD to inform decisions regarding AP in abdominal surgery. In this case, the findings support avoiding cefoxitin, avoiding clindamycin for anaerobic coverage, selecting 2 g doses of cefazolin even in patients <80 kg and using 3 mg/kg doses of gentamicin.

Tigecycline use in the outpatient parenteral antibiotic therapy setting

In the context of globally increasing antimicrobial resistance, tigecycline appears to be a useful therapeutic option. The need for prolonged courses for complex infections has prompted consideration of its use via outpatient parenteral antibiotic therapy (OPAT) programmes, although clinical outcomes when used in this setting remain unknown. We retrospectively reviewed the patient characteristics and outcomes of 11 patients who received tigecycline, most commonly delivered as 100 mg once daily, via OPAT at three tertiary Australian hospitals. Rates of co-morbidity and prior antibiotic use were high. Patients had a wide range of infections including bone and/or joint (n = 5), intra-abdominal (n = 3), lower respiratory tract (n = 2) and parapharyngeal abscess (n = 1). Mycobacterial species (n = 5) were the most frequent pathogen, and multi-resistant organisms were common (n = 4). The median OPAT duration was 14 days (IQR 6-30). Nausea was encountered in 45 % of cases. At completion of OPAT, 1 patient (9 %) was cured, 2 (18 %) had improved and 8 (73 %) failed therapy. Failure occurred due to either progression or non-response of infection (n = 4), re-admission (n = 3), premature cessation of tigecycline due to nausea (n = 3) or death (n = 1). Whilst OPAT delivery of tigecycline is a therapeutic option, when used as second-line therapy for complex, often multi-resistant infections in patients with multiple comorbidities, high rates of clinical failure, readmissions and adverse effects, especially nausea, should be anticipated.

Global survey on nebulization of antimicrobial agents in mechanically ventilated patients: a call for international guidelines

Nebulized antimicrobial agents are increasingly administered for treatment of respiratory infections in mechanically ventilated (MV) patients. A structured online questionnaire assessing the indications, dosages and recent patterns of use for nebulized antimicrobial agents in MV patients was developed. The questionnaire was distributed worldwide and completed by 192 intensive care units. The most common indications for using nebulized antimicrobial agent were ventilator-associated tracheobronchitis (VAT; 58/87), ventilator-associated pneumonia (VAP; 56/87) and management of multidrug-resistant, Gram-negative (67/87) bacilli in the respiratory tract. The most common prescribed nebulized agents were colistin methanesulfonate and sulfate (36/87, 41.3% and 24/87, 27.5%), tobramycin (32/87, 36.7%) and amikacin (23/87, 26.4%). Colistin methanesulfonate, amikacin and tobramycin daily doses for VAP were significantly higher than for VAT (p < 0.05). Combination of parenteral and nebulized antibiotics occurred in 50 (86%) of 58 prescriptions for VAP and 36 (64.2%) of 56 of prescriptions for VAT. The use of nebulized antimicrobial agents in MV patients is common. There is marked heterogeneity in clinical practice, with significantly different in use between patients with VAP and VAT. Randomized controlled clinical trials and international guidance on indications, dosing and antibiotic combinations to improve clinical outcomes are urgently required.

Population pharmacokinetics of linezolid in critically ill patients on renal replacement therapy: comparison of equal doses in continuous venovenous haemofiltration and continuous venovenous haemodiafiltration

OBJECTIVES

Few data are available to guide linezolid dosing during renal replacement therapy. The objective of this study was to compare the population pharmacokinetics of linezolid during continuous venovenous haemofiltration (CVVHF, 30 mL/kg/h) and continuous venovenous haemodiafiltration (CVVHDF, 15 mL/kg/h + 15 mL/kg/h).

METHODS

Patients requiring linezolid 600 mg iv every 12 h and CVVHF or CVVHDF were eligible for this prospective study. Seven blood samples were collected over one dosing interval and analysed by a validated chromatographic method. Population pharmacokinetic analysis was undertaken using Pmetrics. Monte Carlo simulations evaluated achievement of a pharmacodynamics target of an AUC from 0-24 h to MIC (AUC0-24/MIC) of 80.

RESULTS

Nine CVVHDF and eight CVVHF treatments were performed in 13 patients. Regimens of CVVHDF and CVVHF were similar. A two-compartment linear model best described the data. CVVHDF was associated with a 20.5% higher mean linezolid clearance than CVVHF, without statistical significance (P = 0.39). Increasing patient weight and decreasing SOFA score were associated with increasing linezolid clearance. The mean (SD) parameter estimates were: clearance (CL), 3.8 (2.2) L/h; volume of the central compartment, 26.5 (10.3) L; intercompartmental clearance constants from central to peripheral, 8.1 (12.1) L/h; and peripheral to central compartments, 3.6 (4.0) L/h. Achievement of pharmacodynamic targets was poor for an MIC of 2 mg/L with the studied dose.

CONCLUSIONS

During CVVHF and CVVHDF, there is profound pharmacokinetic variability of linezolid. Suboptimal achievement of therapeutic targets occurs at the EUCAST breakpoint MIC of 2 mg/L using 600 mg iv every 12 h.

Factors associated with vancomycin nephrotoxicity in the critically ill

Vancomycin is a glycopeptide antibiotic commonly used in the management of methicillin-resistant Staphylococcus aureus infection. The recent increase in prevalence of methicillin-resistant Staphylococcus aureus with reduced susceptibility to vancomycin has prompted experts to advocate for higher target trough serum concentrations. This study aimed to evaluate the potential consequences of more aggressive vancomycin therapy, by examining the association between higher serum concentrations and acute kidney injury (AKI) in a population of critically ill patients. We collected data for all patients who received vancomycin over a five-year period and evaluated the prevalence of new-onset AKI using the Risk, Injury, Failure, Loss and End-stage (RIFLE) kidney disease criteria. One-hundred and fifty-nine patients provided complete data, with 8.8% manifesting new onset AKI while receiving vancomycin. The median age was 57 (44 to 68) years, while the median trough serum concentration was 16 (10 to 19) mg/l. Multivariate logistic regression analysis identified mean trough concentration (OR=1.174, P=0.024), APACHE II score (OR=1.141, P=0.012) and simultaneous aminoglycoside prescription (OR=18.896, P=0.002) as significant predictors of AKI. These data suggest higher trough vancomycin serum concentrations are associated with greater odds of AKI in the critically ill.

Antibiotic dose optimization in critically ill patients

The judicious use of existing antibiotics is essential for preserving their activity against infections. In the era of multi-drug resistance, this is of particular importance in clinical areas characterized by high antibiotic use, such as the ICU. Antibiotic dose optimization in critically ill patients requires sound knowledge not only of the altered physiology in serious infections - including severe sepsis, septic shock and ventilator-associated pneumonia - but also of the pathogen-drug exposure relationship (i.e. pharmacokinetic/pharmacodynamic index). An important consideration is the fact that extreme shifts in organ function, such as those seen in hyperdynamic patients or those with multiple organ dysfunction syndrome, can have an impact upon drug exposure, and constant vigilance is required when reviewing antibiotic dosing regimens in the critically ill. The use of continuous renal replacement therapy and extracorporeal membrane oxygenation remain important interventions in these patients; however, both of these treatments can have a profound effect on antibiotic exposure. We suggest placing emphasis on the use of therapeutic drug monitoring and dose individualization when optimizing therapy in these settings.

Consensus guidelines for optimising antifungal drug delivery and monitoring to avoid toxicity and improve outcomes in patients with haematological malignancy, 2014

Antifungal agents may be associated with significant toxicity or drug interactions leading to sub-therapeutic antifungal drug concentrations and poorer clinical outcomes for patients with haematological malignancy. These risks may be minimised by clinical assessment, laboratory monitoring, avoidance of particular drug combinations and dose modification. Specific measures, such as the optimal timing of oral drug administration in relation to meals, use of pre-hydration and electrolyte supplementation may also be required. Therapeutic drug monitoring (TDM) of antifungal agents is warranted, especially where non-compliance, non-linear pharmacokinetics, inadequate absorption, a narrow therapeutic window, suspected drug interaction or unexpected toxicity are encountered. Recommended indications for voriconazole and posaconazole TDM in the clinical management of haematology patients are provided. With emerging knowledge regarding the impact of pharmacogenomics upon metabolism of azole agents (particularly voriconazole), potential applications of pharmacogenomic evaluation to clinical practice are proposed.

Albumin concentration significantly impacts on free teicoplanin plasma concentrations in non-critically ill patients with chronic bone sepsis

The impact of decreased serum albumin concentrations on free antibiotic concentrations in non-critically ill patients is poorly described. This study aimed to describe the pharmacokinetics of a high-dose regimen of teicoplanin, a highly protein-bound antibiotic, in non-critically ill patients with hypoalbuminaemia. Ten patients with chronic bone sepsis and decreased serum albumin concentrations (<35 g/L) receiving teicoplanin 12 mg/kg 12-hourly intravenously for 48 h followed by 12 mg/kg once daily were enrolled. Surgical debridement was performed on Day 3. Samples of venous blood were collected pre-infusion and post-infusion during the first 4 days of therapy. Total and free teicoplanin concentrations were assayed using validated chromatographic methods. The median serum albumin concentration for the cohort was 18 (IQR 15-24) g/L. After 48 h, the median (IQR) free trough (fC(min)) and total trough (tC(min)) concentrations were 2.90 (2.67-3.47) mg/L and 15.54 (10.28-19.12) mg/L, respectively, although trough concentrations declined thereafter. Clearance of the free concentrations was significantly high relative to the total fraction at 38.6 (IQR 29.9-47.8) L/h and 7.0 (IQR 6.8-9.8) L/h, respectively (P<0.001). Multiple linear regression analysis demonstrated that whereas total teicoplanin concentration did not impact on free concentrations (P=0.174), albumin concentration did (P<0.001). This study confirms the significant impact of hypoalbuminaemia on free concentrations of teicoplanin in non-critically ill patients, similar to that in critically ill patients. Furthermore, the poor correlation with total teicoplanin concentration suggests that therapeutic drug monitoring of free concentrations should be used in these patients.

Extended versus bolus infusion of meropenem and piperacillin: a pharmacokinetic analysis

BACKGROUND

Extended infusion of beta-lactam antibiotics has been advocated as a method for optimizing antibiotic exposure in critically ill patients. The objective of this study was to compare the pharmacokinetics/pharmacodynamics of extended infusion versus bolus infusion of piperacillin and meropenem in critically ill patients with normal renal function.

METHODS

A prospective study of 3 hours extended infusion of meropenem and piperacillin in critically ill patients without renal dysfunction. Results from the extended infusion cohort were compared to previously published bolus infusion data in critically ill patients.

RESULTS

Twenty extended infusion patients (15 piperacillin, 5 meropenem) were compared with 13 bolus infusion patients (8 piperacillin, 5 meropenem). The demographic and clinical characteristics between both groups were not statistically different. Significant pharmacokinetic differences were observed in median (interquartile range) Cmax for both meropenem (extended infusion 17 [12.6-21.9] vs. bolus 85.2 [66.7-140.3]; P=0.01) and piperacillin (extended infusion 76.2 [57.7-92.6] vs. bolus 240.2 [168.5-275.4]; P=0.001). Considerable pharmacokinetic variability existed in each group for both drugs. Compared to bolus infusion, fT>MIC using extended infusion was higher for both drugs: 96% (IQR 71-100%) compared to 77% (IQR 41-93%) for piperacillin (P=0.05) and 82% (IQR 63-89%) compared to 51% (IQR 48-63%) for meropenem (P=0.095); assuming a MIC of 16 mg/L and 2 mg/L respectively.

CONCLUSION

This study confirms that extended infusion in critically ill patients result in advantageous pharmacokinetic profiles by increasing the fT>MIC for piperacillin and meropenem. In a significant subpopulation of critically ill patients with normal renal function, a 100% fT>MIC target is not reached, even with 3-hour extended infusions.

Risk factors for target non-attainment during empirical treatment with β-lactam antibiotics in critically ill patients

PURPOSE

Risk factors for β-lactam antibiotic underdosing in critically ill patients have not been described in large-scale studies. The objective of this study was to describe pharmacokinetic/pharmacodynamic (PK/PD) target non-attainment envisioning empirical dosing in critically ill patients and considering a worst-case scenario as well as to identify patient characteristics that are associated with target non-attainment.

METHODS

This analysis uses data from the DALI study, a prospective, multi-centre pharmacokinetic point-prevalence study. For this analysis, we assumed that these were the concentrations that would be reached during empirical dosing, and calculated target attainment using a hypothetical target minimum inhibitory concentration (MIC), namely the susceptibility breakpoint of the least susceptible organism for which that antibiotic is commonly used. PK/PD targets were free drug concentration maintained above the MIC of the suspected pathogen for at least 50 % and 100 % of the dosing interval respectively (50 % and 100 % f T (>MIC)). Multivariable analysis was performed to identify factors associated with inadequate antibiotic exposure.

RESULTS

A total of 343 critically ill patients receiving eight different β-lactam antibiotics were included. The median (interquartile range) age was 60 (47-73) years, APACHE II score was 18 (13-24). In the hypothetical situation of empirical dosing, antibiotic concentrations remained below the MIC during 50 % and 100 % of the dosing interval in 66 (19.2 %) and 142 (41.4 %) patients respectively. The use of intermittent infusion was significantly associated with increased risk of non-attainment for both targets; creatinine clearance was independently associated with not reaching the 100 % f T( >MIC) target.

CONCLUSIONS

This study found that-in empirical dosing and considering a worst--case scenario--19 % and 41 % of the patients would not achieve antibiotic concentrations above the MIC during 50 % and 100 % of the dosing interval. The use of intermittent infusion (compared to extended and continuous infusion) was the main determinant of non-attainment for both targets; increasing creatinine clearance was also associated with not attaining concentrations above the MIC for the whole dosing interval. In the light of this study from 68 ICUs across ten countries, we believe current empiric dosing recommendations for ICU patients are inadequate to effectively cover a broad range of susceptible organisms and need to be reconsidered.

First Report of Xanthomonas translucens Causing Etiolation on Creeping Bentgrass Turf in Illinois, Kentucky, and North Carolina

Symptoms of etiolation, which is an abnormal elongation and yellowing of tillers, have been observed on creeping bentgrass [Agrostis stolonifera L. (CBG)] putting greens for decades; however, symptoms are typically transient and non-problematic. Reports of etiolation have become more frequent recently and research supports the involvement of bacteria (1). During stressful summer periods in 2011 and 2012, 62 CBG putting green samples were submitted to the NCSU Turf Clinic exhibiting symptoms of etiolation, chlorosis, and/or general decline. Microscopic examination of stem and leaf tissue often showed bacterial streaming from the xylem tissue. Symptomatic tissue was surface disinfested in sodium hypochlorite (10% Clorox) for 5 min, blotted dry, and rinsed in sterile dH₂O. Disinfested tissue was placed in a small drop of sterile dH₂O on a glass microscope slide and cut to allow bacteria to stream into the water for 2 min. The resulting bacterial suspension was streaked onto three nutrient agar (NA) plates and incubated at 30°C overnight. Bacterial colonies varied in morphology and those present in the greatest number based on morphology were re-streaked to isolate individual colonies. Bacterial isolates were tentatively identified to species using rDNA sequencing of 16S and ITS regions (3). Sequencing results showed isolates obtained from 6 locations (in Illinois, Kentucky, and North Carolina) having a positive match (≥99% 16S and ≥93% ITS) to Xanthomonas translucens (GenBank accessions AY572961, HM181927, JX976312, AY253329, and AB680445). Additional research is needed to confirm pathovar designation as X. translucens isolates were similar to both poae and graminis pathovars. A representative isolate (LW10-12A) was also examined for carbon source utilization using the BIOLOG 3rd Gen Microplate (Biolog Inc., Hayward, CA) resulting in a positive identification of X. translucens. Isolate LW10-12A was used to inoculate 6-week-old seeded creeping bentgrass cv. A1 plants maintained at 1 cm height in 3.5 cm diameter containers. Scissors were dipped in a cell suspension (~10⁹ CFU ml^-1 in sterile dH₂O) and used to cut healthy CBG plants at 1 cm height and the remaining suspension was applied to the foliage until runoff using an atomizer bottle. Non-inoculated plants were cut and misted using sterile dH₂O. After inoculation, plants were placed in a sealed clear plastic Camwear container (Cambro Co., Huntington Beach, CA) for 48 h and then transferred to the growth chamber bench (30°C) receiving irrigation twice daily with dH₂O. Etiolation was rated within each of the four replicates by counting the number of etiolated leaves that were easily observed as significantly higher than the rest of the turf canopy. Plants inoculated with X. translucens exhibited etiolation of the youngest leaf within 48 h, whereas the non-inoculated plants did not. Symptoms were similar to observations in the field, as etiolated leaves were chlorotic and easily extracted from the turf surface. Microscopic examination showed bacterial streaming and identification of bacteria, using the previously described methods, was positive for X. translucens. Etiolation symptoms persisted over multiple weeks, but a decline in turf quality was not observed. Etiolation has been previously suggested as a precursor to bacterial wilt, caused by X. translucens pv. poae, on annual bluegrass [Poa annua L. f. reptans (Hausskn) T. Koyama] (2) and Acidovorax avenae has also been shown to produce etiolation on CBG (1). To our knowledge, this is the first confirmation of X. translucens as a cause of etiolation in CBG. References: (1) P. R. Giordano et al. Plant Dis. 96:1736, 2012. (2) N. A. Mitkowski et al. Plant Dis. 89:469, 2005. (3) N. W. Schaad et al. Lab. Guide for Ident. of Plant Path Bac., 2001.

Variability in protein binding of teicoplanin and achievement of therapeutic drug monitoring targets in critically ill patients: lessons from the DALI Study

The aims of this study were to describe the variability in protein binding of teicoplanin in critically ill patients as well as the number of patients achieving therapeutic target concentrations. This report is part of the multinational pharmacokinetic DALI Study. Patients were sampled on a single day, with blood samples taken both at the midpoint and the end of the dosing interval. Total and unbound teicoplanin concentrations were assayed using validated chromatographic methods. The lower therapeutic range of teicoplanin was defined as total trough concentrations from 10 to 20 mg/L and the higher range as 10-30 mg/L. Thirteen critically ill patients were available for analysis. The following are the median (interquartile range) total and free concentrations (mg/L): midpoint, total 13.6 (11.2-26.0) and free 1.5 (0.7-2.5); trough, total 11.9 (10.2-22.7) and free 1.8 (0.6-2.6). The percentage free teicoplanin for the mid-dose and trough time points was 6.9% (4.5-15.6%) and 8.2% (5.5-16.4%), respectively. The correlation between total and free antibiotic concentrations was moderate for both the midpoint (ρ = 0.79, P = 0.0021) and trough (ρ = 0.63, P = 0.027). Only 42% and 58% of patients were in the lower and higher therapeutic ranges, respectively. In conclusion, use of standard dosing for teicoplanin leads to inappropriate concentrations in a high proportion of critically ill patients. Variability in teicoplanin protein binding is very high, placing significant doubt on the validity of total concentrations for therapeutic drug monitoring in critically ill patients.

Phenytoin loading doses in adult critical care patients: does current practice achieve adequate drug levels?

Phenytoin is regularly employed in the critically ill for prophylaxis against or treatment of seizure disorders. No prior studies have examined current dosing practices in an Australasian intensive care unit (ICU) setting. The aims of this study were to: a) describe the adequacy of contemporary dosing in respect to free and total serum phenytoin concentrations; b) identify factors associated with therapeutic drug concentrations; and c) examine the accuracy of predictive equations that estimate free concentrations in this setting. All patients receiving a loading dose of phenytoin in a tertiary-level ICU were eligible for enrolment; 53 patients were enrolled in the study. Serum samples to determine free and total phenytoin concentrations (measured by high performance liquid chromatography) were then drawn prior to the following dose. Free concentrations below the recommended target (<1 mg/l) were considered as suboptimal. The most common indication for phenytoin loading was traumatic brain injury (49%) and the mean administered dose was 14.5 (3.66) mg/kg. Twenty-six patients (49%) had suboptimal trough free concentrations, although this subgroup was significantly heavier and therefore received a lower per kilogram dose (12.8 [3.1] vs 16.3 [3.4] mg/kg, P=0.001). In multivariate analysis, larger weight adjusted doses (P=0.018), higher albumin concentration (P=0.034) and receiving phenytoin for an indication other than seizure (P=0.035), were associated with a greater likelihood of adequate concentrations. In conclusion, phenytoin dosing remains complex in critically ill patients, although lower per kilogram loading doses are strongly associated with free concentrations below the desired target.

Increased sedation requirements in patients receiving extracorporeal membrane oxygenation for respiratory and cardiorespiratory failure

Critically ill patients receiving extracorporeal membrane oxygenation (ECMO) are often noted to have increased sedation requirements. However, data related to sedation in this complex group of patients is limited. The aim of our study was to characterise the sedation requirements in adult patients receiving ECMO for cardiorespiratory failure. A retrospective chart review was performed to collect sedation data for 30 consecutive patients who received venovenous or venoarterial ECMO between April 2009 and March 2011. To test for a difference in doses over time we used a regression model. The dose of midazolam received on ECMO support increased by an average of 18 mg per day (95% confidence interval 8, 29 mg, P=0.001), while the dose of morphine increased by 29 mg per day (95% confidence interval 4, 53 mg, P=0.021) The venovenous group received a daily midazolam dose that was 157 mg higher than the venoarterial group (95% confidence interval 53, 261 mg, P=0.005). We did not observe any significant increase in fentanyl doses over time (95% confidence interval 1269, 4337 µg, P=0.94). There is a significant increase in dose requirement for morphine and midazolam during ECMO. Patients on venovenous ECMO received higher sedative doses as compared to patients on venoarterial ECMO. Future research should focus on mechanisms behind these changes and also identify drugs that are most suitable for sedation during ECMO.

A comparison of pulse contour wave analysis and ultrasonic cardiac output monitoring in the critically ill

Cardiac output (CO) is a key determinant of major organ blood flow and solute delivery to drug eliminating organs. As such, CO assessment is a key covariate in understanding altered drug handling in the critically ill. Newer minimally-invasive devices are providing unique platforms for such an application, although comparison data are currently lacking. In this study we evaluated the Vigileo (Edwards Lifesciences, Irvine, CA, USA) and USCOM (USCOM Ltd, Sydney, NSW) devices in 62 critically ill patients requiring antibacterial therapy. The mean COVigileo and COUSCOM for the first paired measurements were 8.20±2.65 l/minute and 6.84±2.57 l/minute respectively (P <0.001). A significant correlation was evident in all patients (r=0.537, P <0.001) although the recorded bias was large (1.36±2.51 l/minute, limits of agreement -3.6 to±6.3 l/minute). The overall percentage error was 65%. There was an improved correlation in those admitted with sepsis (r=0.639, P <0.001), compared to trauma (r=0.373, P=0.066), although bias, precision and percentage error were similar in both subgroups. In 54 patients a second paired assessment was obtained at three hours. A weak, although significant correlation (r=0.377, P=0.005) was observed suggesting that gross trends over time were similar. In conclusion, our findings demonstrate poor agreement between these techniques suggesting that these devices are not simply interchangeable when assessing CO in a research or clinical setting.

The potential for underutilized crops to improve security of food production

Staple crops face major challenges in the near future and a diversification away from over-reliance on staples will be important as part of the progress towards the goal of achieving security of food production. Underutilized or neglected crops species are often indigenous ancient crop species which are still used at some level within the local, national or even international communities, but have the potential to contribute further to the mix of food sources than they currently do. The most cost-effective and easily disseminated changes that can be made to a crop are changes to the genetics, as these are contained within the seed itself and, for many species, the seed is a pure breeding, self-replicating, resource. This article focuses on the potential of underutilized crops to contribute to food security and, in particular, whether genetics and breeding can overcome some of the constraints to the enhanced uptake of these species in the future. The focus here is on overview rather than detail and subsequent articles will examine the current evidence base.

Do we understand the impact of altered physiology, consequent interventions and resultant clinical scenarios in the intensive care unit? The antibiotic story

Early, appropriate antibacterial therapy is a key factor in effectively managing septic critically ill patients1. The prescriber must not only employ an agent of appropriate spectrum, but also in an adequate dose to achieve bacterial eradication at the site of infection. However, the relationship between drug administration and therapeutic success is complex in the critically ill, such that a patient's physiology heavily influences the way drugs distribute into tissue and are eliminated. This represents a significant challenge to the emergency or intensive care physician, and in this manner, personalising therapy, through a greater understanding of how a drug will behave in an individual patient, is likely to lead to improved outcomes.

Corticothalamic dynamics: structure of parameter space, spectra, instabilities, and reduced model

Linear instabilities are analyzed in a physiologically based mean-field corticothalamic model and a reduced-parameter model derived from it. In both models, the stable zone corresponding to normal arousal states is bounded by a series of surfaces demarcating the onsets of instabilities. The stable zone is found to depend on delay and rate parameters, whose values have a simple relationship to the number of instabilities and dominant frequencies on the stable zone's boundary. The dominant frequencies of linear activity inside the stable zone are found to lie in clearly delineated regions, each corresponding to an instability surface on its boundary and having approximately the same dominant frequency. These regions are ordered in parameter space according to their dominant frequencies, and an instability associated with the intrathalamic loop is shown to have the highest frequency that can become unstable. This reveals an important role for the thalamus in controlling the stability and bandwidth of dynamics in the corticothalamic system as a whole. The reduced model is found to agree well with the full model in a wide region of parameter space and, thus, is a useful guide to the full model's dynamics.

Continuous infusion vs. bolus dosing: implications for beta-lactam antibiotics

Beta-lactam antibiotics display time-dependant pharmacodynamics whereby constant antibiotic concentrations rather than high peak concentrations are most likely to result in effective treatment of infections caused by susceptible bacteria. Continuous administration has been suggested as an alternative strategy, to conventional intermittent dosing, to optimise beta-lactam pharmacokinetic/pharmacodynamic (PK/PD) properties. With the availability of emerging data, we elected to systematically investigate the published literature describing the comparative PK/PD and clinical outcomes of beta-lactam antibiotics administered by continuous or intermittent infusion. We found that the studies have been performed in various patient populations including critically ill, cancer and cystic fibrosis patients. Available in vitro PK/PD data conclusively support the administration of beta-lactams via continuous infusion for maximizing bacterial killing from consistent attainment of pharmacodynamic end-points. In addition, clinical outcome data supports equivalence, even with the use of a lower dose by continuous infusion. However, the present clinical data is limited with small sample sizes common with insufficient power to detect advantages in favour of either dosing strategy. With abundant positive pre-clinical data as well as document in vivo PK/PD advantages, large multi-centre trials are needed to describe whether continuous administration of beta-lactams is truly more effective than intermittent dosing.

Applications and implications of direct groundwater velocity measurement at the centimetre scale

Three projects involving point velocity probes (PVPs) illustrate the advantages of direct groundwater velocity measurements. In the first, a glacial till and outwash aquifer was characterized using conventional methods and multilevel PVPs for designing a bioremediation program. The PVPs revealed a highly conductive zone that dominated the transport of injected substances. These findings were later confirmed with a natural gradient tracer test. In the second, PVPs were used to map a groundwater velocity field around a dipole recirculation well. The PVPs showed higher than expected velocities near the well, assuming homogeneity in the aquifer, leading to improved representations of the aquifer heterogeneity in a 3D flow model, and an improved match between the modelled and experimental tracer breakthrough curves. In the third study, PVPs detected subtle changes in aquifer permeability downgradient of a biostimulation experiment. The changes were apparently reversible once the oxygen source was depleted, but in locations where the oxygen source lingered, velocities remained low. PVPs can be a useful addition to the hydrogeologist's toolbox, because they can be constructed inexpensively, they provide data in support of models, and they can provide information on flow in unprecedented detail.

Quantitative modelling of sleep dynamics

Arousal is largely controlled by the ascending arousal system of the hypothalamus and brainstem, which projects to the corticothalamic system responsible for electroencephalographic (EEG) signatures of sleep. Quantitative physiologically based modelling of brainstem dynamics theory is described here, using realistic parameters, and links to EEG are outlined. Verification against a wide range of experimental data is described, including arousal dynamics under normal conditions, sleep deprivation, stimuli, stimulants and jetlag, plus key features of wake and sleep EEGs.

Transient heterogeneity in an aquifer undergoing bioremediation of hydrocarbons

Localized, transient heterogeneity was studied in a sand aquifer undergoing benzene, toluene, ethylbenzene, and xylene bioremediation using a novel array of multilevel, in situ point velocity probes (PVPs). The experiment was conducted within a sheet-pile alleyway to maintain a constant average flow direction through time. The PVPs measured changes in groundwater velocity direction and magnitude at the centimeter scale, making them ideal to monitor small-scale changes in hydraulic conductivity (K). Velocities were shown to vary nonuniformly by up to a factor of 3 when a source of oxygen was established down-gradient of the petroleum spill. In spite of these local variations, the average groundwater velocity within the 7 m × 20 m sheet-piled test area only varied within ± 25%. The nonuniform nature of the velocity variations across the gate indicated that the changes were not due solely to seasonal hydraulic gradient fluctuations. At the conclusion of the experiment, microbial biomass levels in the aquifer sediments was approximately 1 order of magnitude higher in the oxygen-amended portion of the aquifer than at the edge of the plume or in locations up-gradient of the source. These data suggest that the transient velocities resulted, at least in part, from enhanced biological activity that caused transient heterogeneities in the porous medium.