Transcriptome profiles of macrophages upon infection by morphotypic smooth and rough variants of Mycobacterium abscessus

Mycobacterium abscessus (Mab) infection can be deadly in patients with chronic lung diseases like cystic fibrosis (CF). In vitro and in vivo, Mab may adopt a smooth (S) or rough (R) morphotype, the latter linked to more severe disease conditions. In vitro studies revealed differences in pathogenicity and immune response to S and R morphotypes. We propose that in vivo both morphotypes exist and may transiently switch depending on the environment, having important pathogenic and immunologic consequences. This can be modeled by morphotypic S and R variants of Mab selected based on in vitro growth conditions. Here, we report the first analysis of early transcriptional events in mouse bone marrow derived macrophages (BMDMs) upon infection with media-selected interchangeable Mab-S and Mab-R morphotypes. The early transcriptional events after infection with both morphotypes showed considerable overlap of the pro-inflammatory genes that were differentially regulated compared to the uninfected macrophages. We also observed signature genes significantly differentially regulated in macrophages during infection of media-selected morphotypic Mab-S and Mab-R variants. In conclusion, media-selected Mab-S and Mab-R behave in a similar fashion to stable S and R types with respect to pathogenesis and immune response, serving as a useful model for environmentally influenced morphotype selection.

RPEM: Randomized Monte Carlo parametric expectation maximization algorithm

Inspired from quantum Monte Carlo, by sampling discrete and continuous variables at the same time using the Metropolis-Hastings algorithm, we present a novel, fast, and accurate high performance Monte Carlo Parametric Expectation Maximization (MCPEM) algorithm. We named it Randomized Parametric Expectation Maximization (RPEM). We compared RPEM with NONMEM's Importance Sampling Method (IMP), Monolix's Stochastic Approximation Expectation Maximization (SAEM), and Certara's Quasi-Random Parametric Expectation Maximization (QRPEM) for a realistic two-compartment voriconazole model with ordinary differential equations using simulated data. We show that RPEM is as fast and as accurate as the algorithms IMP, QRPEM, and SAEM for the voriconazole model in reconstructing the population parameters, for the normal and log-normal cases.

Time-dependent pharmacodynamics of amikacin on Mycobacterium abscessus growth and resistance emergence

Mycobacterium abscessus pulmonary disease is increasing in prevalence globally, particularly for individuals with cystic fibrosis. These infections are challenging to treat due to a high rate of resistance. Amikacin is critical to treatment, but the development of toxicity, amikacin resistance, and treatment failure are significant challenges. Amikacin has been characterized previously as peak-dependent and extended-interval dosing is commonly used. In our hollow fiber infection model of M. abscessus, amikacin exhibited time-dependent rather than the expected peak-dependent pharmacodynamics. Humanized amikacin exposures with more frequent, short-interval dosing (continuous infusion or every 12 hours) yielded improved microbiological response compared to extended-interval dosing (every 24 hours or 1-3 times per week). Short-interval dosing inhibited growth with a mean (SD) maximum Δlog10 colony forming units of -4.06 (0.52), significantly more than extended-interval dosing (P = 0.0013) every 24 hours, -2.40 (0.58), or 1-3 times per week, -2.39 (0.38). Growth recovery, an indicator of resistance emergence, occurred at 6.56 (0.70) days with short-interval dosing but was significantly earlier with extended-interval dosing (P = 0.0032) every 24 hours, 3.88 (0.85) days, and 1-3 times per week, 3.27 (1.72) days. Microbiological response correlated best with the pharmacodynamic index of %T > minimum inhibitory concentration (MIC), with an EC80 for growth inhibition of ~40%T > MIC. We used a previously published population model of amikacin to determine the probability of achieving 40%T > MIC and show that current dosing strategies are far below this target, which may partially explain why treatment failure remains so high for these infections. These data support a cautious approach to infrequent amikacin dosing for the treatment of M. abscessus.IMPORTANCEPulmonary disease caused by Mycobacterium abscessus complex (MABSC) is increasing worldwide, particularly in patients with cystic fibrosis. MABSC is challenging to treat due to high levels of antibiotic resistance. Treatment requires 2-4 antibiotics over more than 12 months and has a significant risk of toxicity but still fails to eradicate infection in over 50% of patients with cystic fibrosis. Antibiotic dosing strategies have been largely informed by common bacteria such as Pseudomonas aeruginosa. The "pharmacodynamic" effects of amikacin, a backbone of MABSC treatment, were thought to be related to maximum "peak" drug concentration, leading to daily or three times weekly dosing. However, we found that amikacin MABSC kill and growth recovery, an indicator of antibiotic resistance, are dependent on how long amikacin concentrations are above the minimum inhibitory concentration, not how high the peak concentration is. Therefore, we recommend a re-evaluation of amikacin dosing to determine if increased frequency can improve efficacy.

Individual meropenem epithelial lining fluid and plasma PK/PD target attainment

It is unclear whether plasma is a reliable surrogate for target attainment in the epithelial lining fluid (ELF). The objective of this study was to characterize meropenem target attainment in plasma and ELF using prospective samples. The first 24-hour T>MIC was evaluated vs 1xMIC and 4xMIC targets at the patient (i.e., fixed MIC of 2 mg/L) and population [i.e., cumulative fraction of response (CFR) according to EUCAST MIC distributions] levels for both plasma and ELF. Among 65 patients receiving ≥24 hours of treatment, 40% of patients failed to achieve >50% T>4xMIC in plasma and ELF, and 30% of patients who achieved >50% T>4xMIC in plasma had <50% T>4xMIC in ELF. At 1xMIC and 4xMIC targets, 3% and 25% of patients with >95% T>MIC in plasma had <50% T>MIC in ELF, respectively. Those with a CRCL >115 mL/min were less likely to achieve >50%T>4xMIC in ELF (P < 0.025). In the population, CFR for Escherichia coli at 1xMIC and 4xMIC was >97%. For Pseudomonas aeruginosa, CFR was ≥90% in plasma and ranged 80%-85% in ELF at 1xMIC when a loading dose was applied. CFR was reduced in plasma (range: 75%-81%) and ELF (range: 44%-60%) in the absence of a loading dose at 1xMIC. At 4xMIC, CFR for P. aeruginosa was 60%-86% with a loading dose and 18%-62% without a loading dose. We found that plasma overestimated ELF target attainment inup to 30% of meropenem-treated patients, CRCL >115 mL/min decreased target attainment in ELF, and loading doses increased CFR in the population.

Optimizing Vancomycin Therapy in Critically Ill Children: A Population Pharmacokinetics Study to Inform Vancomycin Area under the Curve Estimation Using Novel Biomarkers

Area under the curve (AUC)-directed vancomycin therapy is recommended, but Bayesian AUC estimation in critically ill children is difficult due to inadequate methods for estimating kidney function. We prospectively enrolled 50 critically ill children receiving IV vancomycin for suspected infection and divided them into model training (n = 30) and testing (n = 20) groups. We performed nonparametric population PK modeling in the training group using Pmetrics, evaluating novel urinary and plasma kidney biomarkers as covariates on vancomycin clearance. In this group, a two-compartment model best described the data. During covariate testing, cystatin C-based estimated glomerular filtration rate (eGFR) and urinary neutrophil gelatinase-associated lipocalin (NGAL; full model) improved model likelihood when included as covariates on clearance. We then used multiple-model optimization to define the optimal sampling times to estimate AUC24 for each subject in the model testing group and compared the Bayesian posterior AUC24 to AUC24 calculated using noncompartmental analysis from all measured concentrations for each subject. Our full model provided accurate and precise estimates of vancomycin AUC (bias 2.3%, imprecision 6.2%). However, AUC prediction was similar when using reduced models with only cystatin C-based eGFR (bias 1.8%, imprecision 7.0%) or creatinine-based eGFR (bias -2.4%, imprecision 6.2%) as covariates on clearance. All three model(s) facilitated accurate and precise estimation of vancomycin AUC in critically ill children.

Model-Informed Rationale for Early Therapeutic Drug Monitoring of Colistin in Critically Ill Patients

Adequate colistin exposure is important for microbiological clearance. This study was performed in critically ill patients >18 years old to develop a simplified nonparametric pharmacokinetic (PK) model of colistin for routine clinical use and to determine the role of dose optimization. The Non-Parametric Adaptive Grid algorithm within the Pmetrics software package for R was used to develop a PK model from 47 patients, and external validation of the final model was performed in 13 patients. A 1-compartment multiplicative gamma error model with 0-order input and first-order elimination of colistin was developed with creatinine clearance and serum albumin as covariates on elimination rate constant. An R² for observed vs individual predicted colistin concentrations of 0.92 was obtained in the validation cohort. High interindividual variability in colistin steady-state area under the plasma concentration-time curve (AUC) from from 120 hours to 144 hours (coefficient of variation = 80.1%) and a high interoccasion variability (median coefficient of variation of AUC from time 0 to hours predicted every 8 hours for initial 96 hours after starting colistin = 23.8) was predicted in patients who received this antibiotic for a period of over 152 hours (n = 22). With the model-suggested dose regimen, only 20% of simulated profiles achieved AUC from time 0 to 24 hours in the range of 50 to 60 mg • h/L due to high variability in population PK. In this group of patients, steady-state colistin concentrations were predicted to be achieved >96 hours after initiation of colistimethate sodium. This study advocates the need for early and repeated therapeutic drug monitoring and dose optimization in critically ill patients to achieve adequate therapeutic concentration of colistin.

Interchangeability of generic drugs for subpopulations: Bioequivalence simulation from a nonparametric PK model of gabapentin generic drugs

Patients are often switched between generic formulations of the same drug, but in some cases generic interchangeability is questioned. For generic drugs to be approved, bioequivalence with the innovator drug should be demonstrated, but evidence of bioequivalence is not required in the intended patient population or relative to other approved generics.

AIM

We aim to identify pathophysiological pharmacokinetic subpopulations for whom there is a difference in comparative bioavailability compared to a healthy population.

METHODS

We used simulated exposures from a nonparametric model of multiple generics and the originator gabapentin. Exposure was simulated for virtual populations with pharmacokinetic characteristics beyond those of healthy subjects with regard to rate of absorption, volume of distribution and reduced renal function. Virtual parallel design bioequivalence studies were performed using a random sample of 24 simulated subjects, with standard acceptance criteria.

RESULTS

Results indicated increased pharmacokinetic variability for patient populations with a lower rate of absorption or a reduced renal function, but no change in the average comparable bioavailability ratio. This increased variability results in a reduced likelihood of demonstrating bioequivalence. Observations were similar for comparisons between all different formulations, as well as between subjects who received the identical formulation in a repeated fashion. No relevant effect was observed for simulations with increased volume of distribution.

CONCLUSION

Our simulations indicate that the reduced likelihood of demonstrating bioequivalence for subjects with altered pharmacokinetics is not influenced by a formulation switch, nor does the average comparable bioavailability ratio change, therefore these results support generic interchangeability and current approval requirements for generics.

Individual target pharmacokinetic/pharmacodynamic attainment rates among meropenem-treated patients admitted to the ICU with hospital-acquired pneumonia

OBJECTIVES

Critical illness reduces β-lactam pharmacokinetic/pharmacodynamic (PK/PD) attainment. We sought to quantify PK/PD attainment in patients with hospital-acquired pneumonia.

METHODS

Meropenem plasma PK data (n = 70 patients) were modelled, PK/PD attainment rates were calculated for empirical and definitive targets, and between-patient variability was quantified [as a coefficient of variation (CV%)].

RESULTS

Attainment of 100% T&gt;4×MIC was variable for both empirical (CV% = 92) and directed (CV% = 33%) treatment.

CONCLUSIONS

Individualization is required to achieve suggested PK/PD targets in critically ill patients.

Pharmacokinetic modelling of caspofungin to develop an extended dosing regimen in paediatric patients

BACKGROUND

Echinocandins are commonly used in treatment and prophylaxis of invasive fungal diseases. Intravenous daily dosing for prophylaxis in the outpatient setting can however become a hurdle for adequate compliance in the paediatric population.

OBJECTIVES

Simulations were performed to assess extended twice-weekly dosing for antifungal prophylaxis using caspofungin.

METHODS

A population pharmacokinetic model was developed based on previously published data from children aged 3 months to 17 years. Using the final model, Monte Carlo simulations were performed to assess the dose needed for adequate exposure in a twice-weekly setting. Mean weekly AUC0-24 h/MIC together with reported AUC0-24 h from previously reported paediatric trials were used to guide adequate exposure.

RESULTS AND CONCLUSIONS

A two-compartment model with linear elimination and allometric scaling using fixed exponents was found most adequate to describe the given paediatric populations. Simulations showed that a 200 mg/m2 twice-weekly regimen with maximal 200 mg total dose should result in exposures matching registered daily dosing as well as commonly used pharmacokinetic/pharmacodynamic targets.

Growth medium and nitric oxide alter Mycobacterium abscessus morphotype and virulence

Mycobacterium abscessus complex (MABC) infections cause significant morbidity and mortality among patients with chronic lung disease, like cystic fibrosis. MABC exists in smooth (S) and rough (R) morphotypes, but triggers of morphotype switching and associated pathogenicity or antimicrobial susceptibility are poorly understood. We demonstrate that M. abscessus subspecies abscessus (Mab), massiliense (Mms), and bolletii (Mbl) cultured in Middlebrook (MB) broth exhibit S morphotype, whereas the bacteria grown in Luria Bertani (LB) broth adopt the R morphotype, characterized by low glycopeptidolipid (GPL) expression. The components of broth that mediate this selection are complex, with albumin supplementation promoting growth of S morphotype, but not sufficient for complete selection. Consistent with the findings of other groups, R forms of Mab, Mms and Mbl selected by LB broth were internalized in RAW 264.7 macrophages with higher efficiency than S. Intracellular survival of broth-selected organisms was variable and was higher for S Mab, but lower for S Mms and Mbl. It is proposed that growth in R morphotype is induced during stress conditions, such as nutrient poor environments or during inflammation. One key component of inflammation is release of nitric oxide. We demonstrated that a nitric oxide donor (DETA-NONOate) appears to induce growth in an R morphotype, as indicated by reduced GPL expression of Mab. Mab treated with DETA-NONOate also enhanced susceptibility to azithromycin at sub-MIC concentrations. In conclusion, morphotype and macrophage intracellular bacterial load of MABC subspecies can be manipulated by growing the bacteria in different culture conditions. Nitric oxide may also drive morphotype selection and enhanced azithromycin activity against Mab and macrophage killing.

A pharmacokinetics-based approach to the monitoring of patient adherence to atorvastatin therapy

The inadequate adherence of patients whose hyperlipidemia is treated with atorvastatin (ATR) to medical instructions presents a serious health risk. Our aim was to develop a flexible approach based on therapeutic drug monitoring (TDM), nonparametric population pharmacokinetic modeling, and Monte Carlo simulation to differentiate adherent patients from partially and nonadherent individuals in a nonrandomized, unicentric, observational study. Sixty-five subjects were enrolled. Nonparametric, mixed-effect population pharmacokinetic models of the sums of atorvastatin and atorvastatin lactone concentrations (ATR+ATRL) and of the concentrations of the acid and lactone forms of ATR and its 2- and 4-hydroxylated pharmacologically active metabolites (ATR+MET) were elaborated by including the TDM results obtained in 128 samples collected from thirty-nine subjects. Monte Carlo simulation was performed based on the elaborated models to establish the probabilities of attaining a specific ATR+ATRL or ATR+MET concentration in the range of 0.002-10 nmol (mg dose)-1 L-1 at 1-24 h postdose by adherent, partially adherent, and nonadherent patients. The results of the simulations were processed to allow the estimation of the adherence of further 26 subjects who were phlebotomized at sampling times of 2-20 h postdose by calculating the probabilities of attaining the ATR+ATRL and ATR+MET concentrations measured in these subjects in adherent, partially adherent, and nonadherent individuals. The best predictive values of the estimates of adherence could be obtained with sampling at early sampling times. 61.54% and 38.46% of subjects in the adherence testing set were estimated to be fully and partially adherent, respectively, while in all cases the probability of nonadherence was extremely low. The evaluation of patient adherence to ATR therapy based on pharmacokinetic modeling and Monte Carlo simulation has important advantages over the collection of trough samples and the use of therapeutic ranges.

Building Optimal Three-Drug Combination Chemotherapy Regimens

Multidrug therapy is often required. Examples include antiviral therapy, nosocomial infections, and, most commonly, anti-Mycobacterium tuberculosis therapy. Our laboratory previously identified a mathematical approach to identify 2-drug regimens with a synergistic or additive interaction using a full factorial study design. Our objective here was to generate a method to identify an optimal 3-drug therapy. We studied M. tuberculosis isolate H37Rv in log-phase growth in flasks. Pretomanid and moxifloxacin were chosen as the base 2-drug regimen. Bedaquiline (plus M2 metabolite) was chosen as the third drug for evaluation. Total bacterial burden and bacterial burden less-susceptible to study drugs were enumerated. A large mathematical model was fit to all the data. This allowed extension to evaluation of the 3-drug regimen by employing a Monte Carlo simulation. Pretomanid plus moxifloxacin demonstrated excellent bacterial kill and suppressed amplification of less-susceptible pathogens. Total bacterial burden was driven to extinction in 3 weeks in 6 of 9 combination therapy evaluations. Only the lowest pretomanid/moxifloxacin exposures in combination did not extinguish the bacterial burden. No combination regimen allowed resistance amplification. Generation of 95% credible intervals about estimates of the interaction parameters α (αs, αr-p, and αr-m) by bootstrapping showed the interaction was near synergistic. The addition of bedaquiline/M2 metabolite was evaluated by forming a 95% confidence interval regarding the decline in bacterial burden. The addition of bedaquiline/M2 metabolite shortened the time to eradication by 1 week and was significantly different. A model-based system approach to evaluating combinations of 3 agents shows promise to rapidly identify the most promising combinations that can then be trialed.

Population Pharmacokinetics of Imipenem in Critically Ill Patients: A Parametric and Nonparametric Model Converge on CKD-EPI Estimated Glomerular Filtration Rate as an Impactful Covariate

BACKGROUND

Population pharmacokinetic (popPK) models for antibiotics are used to improve dosing strategies and individualize dosing by therapeutic drug monitoring. Little is known about the differences in results of parametric versus nonparametric popPK models and their potential consequences in clinical practice. We developed both parametric and nonparametric models of imipenem using data from critically ill patients and compared their results.

METHODS

Twenty-six critically ill patients treated with intravenous imipenem/cilastatin were included in this study. Median estimated glomerular filtration rate (eGFR) measured by the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation was 116 mL/min/1.73 m2 (interquartile range 104-124) at inclusion. The usual dosing regimen was 500 mg/500 mg four times daily. On average, five imipenem levels per patient (138 levels in total) were drawn as peak, intermediate, and trough levels. Imipenem concentration-time profiles were analyzed using parametric (NONMEM 7.2) and nonparametric (Pmetrics 1.5.2) popPK software.

RESULTS

For both methods, data were best described by a model with two distribution compartments and the CKD-EPI eGFR equation unadjusted for body surface area as a covariate on the elimination rate constant (Ke). The parametric population parameter estimates were Ke 0.637 h-1 (between-subject variability [BSV]: 19.0% coefficient of variation [CV]) and central distribution volume (Vc) 29.6 L (without BSV). The nonparametric values were Ke 0.681 h-1 (34.0% CV) and Vc 31.1 L (42.6% CV).

CONCLUSIONS

Both models described imipenem popPK well; the parameter estimates were comparable and the included covariate was identical. However, estimated BSV was higher in the nonparametric model. This may have consequences for estimated exposure during dosing simulations and should be further investigated in simulation studies.

Antimicrobial therapeutic drug monitoring in critically ill adult patients: a Position Paper

Purpose

This Position Paper aims to review and discuss the available data on therapeutic drug monitoring (TDM) of antibacterials, antifungals and antivirals in critically ill adult patients in the intensive care unit (ICU). This Position Paper also provides a practical guide on how TDM can be applied in routine clinical practice to improve therapeutic outcomes in critically ill adult patients.

Methods

Literature review and analysis were performed by Panel Members nominated by the endorsing organisations, European Society of Intensive Care Medicine (ESICM), Pharmacokinetic/Pharmacodynamic and Critically Ill Patient Study Groups of European Society of Clinical Microbiology and Infectious Diseases (ESCMID), International Association for Therapeutic Drug Monitoring and Clinical Toxicology (IATDMCT) and International Society of Antimicrobial Chemotherapy (ISAC). Panel members made recommendations for whether TDM should be applied clinically for different antimicrobials/classes.

Results

TDM-guided dosing has been shown to be clinically beneficial for aminoglycosides, voriconazole and ribavirin. For most common antibiotics and antifungals in the ICU, a clear therapeutic range has been established, and for these agents, routine TDM in critically ill patients appears meritorious. For the antivirals, research is needed to identify therapeutic targets and determine whether antiviral TDM is indeed meritorious in this patient population. The Panel Members recommend routine TDM to be performed for aminoglycosides, beta-lactam antibiotics, linezolid, teicoplanin, vancomycin and voriconazole in critically ill patients.

Conclusion

Although TDM should be the standard of care for most antimicrobials in every ICU, important barriers need to be addressed before routine TDM can be widely employed worldwide.

Electronic supplementary material

The online version of this article (10.1007/s00134-020-06050-1) contains supplementary material, which is available to authorized users.

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.

Development of a methodology to make individual estimates of the precision of liquid chromatography-tandem mass spectrometry drug assay results for use in population pharmacokinetic modeling and the optimization of dosage regimens

Background

The clinical value of therapeutic drug monitoring can be increased most significantly by integrating assay results into clinical pharmacokinetic models for optimal dosing. The correct weighting in the modeling process is 1/variance, therefore, knowledge of the standard deviations (SD) of each measured concentration is important. Because bioanalytical methods are heteroscedastic, the concentration-SD relationship must be modeled using assay error equations (AEE). We describe a methodology of establishing AEE’s for liquid chromatography-tandem mass spectrometry (LC-MS/MS) drug assays using carbamazepine, fluconazole, lamotrigine and levetiracetam as model analytes.

Methods

Following method validation, three independent experiments were conducted to develop AEE’s using various least squares linear or nonlinear, and median-based linear regression techniques. SD’s were determined from zero concentration to the high end of the assayed range. In each experiment, precision profiles of 6 (“small” sample sets) or 20 (“large” sample sets) out of 24 independent, spiked specimens were evaluated. Combinatorial calculations were performed to attain the most suitable regression approach. The final AEE’s were developed by combining the SD’s of the assay results, established in 24 specimens/spiking level and using all spiking levels, into a single precision profile. The effects of gross hyperbilirubinemia, hemolysis and lipemia as laboratory interferences were investigated.

Results

Precision profiles were best characterized by linear regression when 20 spiking levels, each having 24 specimens and obtained by performing 3 independent experiments, were combined. Theil’s regression with the Siegel estimator was the most consistent and robust in providing acceptable agreement between measured and predicted SD’s, including SD’s below the lower limit of quantification.

Conclusions

In the framework of precision pharmacotherapy, establishing the AEE of assayed drugs is the responsibility of the therapeutic drug monitoring service. This permits optimal dosages by providing the correct weighting factor of assay results in the development of population and individual pharmacokinetic models.

Development of Chronic Pseudomonas aeruginosa-Positive Respiratory Cultures in Children with Tracheostomy

BACKGROUND

Up to 90% of children develop Pseudomonas aeruginosa (Pa)-positive respiratory cultures after tracheotomy.

OBJECTIVE

To identify the factors associated with chronic Pa-positive respiratory cultures in the first 2 years after tracheotomy.

METHODS

We conducted a retrospective cohort study of 210 children ≤ 18 years old who underwent tracheotomy at a single freestanding children's hospital that had two or more years of respiratory cultures post-tracheotomy available for analysis. We conducted multivariable logistic regression to test the association between demographic and clinical factors to our primary outcome of chronic Pa infection, defined as > 75% of respiratory cultures positive for Pa in the first 2 years after tracheotomy.

RESULTS

Of the primarily male (61%), Hispanic (68%), and publicly insured (88%) cohort, 18% (n = 37) developed chronic Pa-positive respiratory cultures in the first 2 years. On multivariable logistic regression, pre-tracheotomy Pa-positive respiratory culture (aOR 11.3; 95% CI 4-1.5) and discharge on beta agonist (aOR 6.3; 95% CI 1.1-36.8) were independently associated with chronic Pa-positive respiratory cultures, while discharge on chronic mechanical ventilation was associated with decreased odds (aOR 0.3; 95% CI 0.1-0.7). On sensitivity analysis examining those without a pre-tracheotomy Pa-positive respiratory culture, discharge on MV continued to be associated with decreased odds of chronic Pa (aOR 0.1; 95% CI 0.02-0.4) and three other variables (male gender, chronic lung disease, and discharge on inhaled corticosteroids) were associated with increased odds of chronic Pa.

CONCLUSION

Because pre-tracheotomy Pa growth on respiratory culture is associated with post-tracheotomy chronic Pa-positive respiratory cultures, future research should examine pre-tracheotomy Pa eradication or suppression protocols.

Optimizing Gentamicin Dosing in Pediatrics Using Monte Carlo Simulations

Gentamicin is known to have concentration-dependent bactericidal activity, and its nephrotoxic effect is well described. We developed a population pharmacokinetic/pharmacodynamic model to optimize gentamicin dosing in pediatrics. Data were retrospectively collected for pediatric patients 1 month to 12 years of age, admitted to general pediatric wards or intensive care units and received gentamicin for suspected or proven Gram-negative infections at King Saud University Medical City, Riyadh, Saudi Arabia. A total of 306 gentamicin peak and trough concentrations sets from 107 patients were analyzed with mean (±standard deviation) patient age and weight of 4.5 ± 3.5 years and 16.7 ± 10.8 kg, respectively. Gentamicin pharmacokinetics were adequately described with a one compartment system (R = 0.82, bias = 1.75% and precision = 88% for population predictions and R = 0.94, bias = 5% and precision = 29% for individual predictions). The gentamicin pharmacokinetic parameters were as follows: volume of distribution = 8.9 L, total body clearance = 2.8 L/h for a 20-kg patient. Monte Carlo simulations showed that doses of 5-6 mg/kg/dose once daily are adequate only to treat infections with Gram-negative organisms having minimal inhibitory concentration less than 1 µg/mL. While, at minimal inhibitory concentration of 1 µg/mL, higher doses (7-8 mg/kg/dose once daily) are needed to maximize the efficacy of gentamicin. However, at minimal inhibitory concentration of 2 µg/mL, even a 10 mg/kg dose showed poor target attainment (52%). The finding of this study highlights the need to reevaluate the current breakpoints of gentamicin and also to assess the safety of higher doses of gentamicin in pediatrics.

Early Use of Anti-influenza Medications in Hospitalized Children With Tracheostomy

BACKGROUND

Early administration of anti-influenza medications is recommended for all children hospitalized with influenza. We investigated whether early use of anti-influenza medications is associated with improved outcomes in children with tracheostomy hospitalized with influenza.

METHODS

We performed a multicenter retrospective cohort study through the Pediatric Health Information System database for patients aged 30 days to 19 years who were discharged between October 1, 2007, and September 30, 2015 with diagnostic codes for both influenza and tracheostomy. Our primary predictor was receipt of anti-influenza medications on hospital day 0 or 1. We used propensity score matching to adjust for confounding by indication. Primary outcomes were length of stay (LOS) and 30-day all-cause revisit rate (emergency department visit or hospital admission).

RESULTS

Of 1436 discharges screened, 899 met inclusion criteria. The median admission age was 5 years (interquartile range: 2-10). The majority had multiple complex chronic conditions (median 3; interquartile range: 3-4) and technology dependence, such as gastrostomy tube (73.6%). After matching 772 unique admissions by propensity score, LOS was shorter for the cohort receiving early anti-influenza medications (6.4 vs 7.5 days; P = .01) without increase in revisit rate (27.5% vs 24.1%; P = .28). More than 80% in both cohorts received empirical antibiotics, and the duration of antibiotic therapy was similar (5.0 vs 5.6 days; P = .11).

CONCLUSIONS

Early use of anti-influenza medications in children with tracheostomy hospitalized with influenza is associated with shorter LOS, but these children continue to receive antibiotics despite identification and treatment of their viral infections.

Pharmacodynamics of teicoplanin against MRSA

Objectives

The overall study aim was to identify the relevant preclinical teicoplanin pharmacokinetic (PK)/pharmacodynamic (PD) indices to predict efficacy and suppression of resistance in MRSA infection.

Methods

A hollow-fibre infection model and a neutropenic murine thigh infection model were developed. The PK/PD data generated were modelled using a non-parametric population modelling approach with Pmetrics. The posterior Bayesian estimates derived were used to study the exposure-effect relationships. Monte Carlo simulations from previously developed population PK models in adults and children were conducted to explore the probability of target attainment (PTA) for teicoplanin dosage regimens against the current EUCAST WT susceptibility range.

Results

There was a concentration-dependent activity of teicoplanin in both the in vitro and in vivo models. A total in vivo AUC/MIC of 610.4 (total AUC of 305.2 mg·h/L) for an MRSA strain with an MIC of 0.5 mg/L was needed for efficacy (2 log10 cell kill) against a total bacterial population. A total AUC/MIC ratio of ∼1500 (total AUC of ∼750 mg·h/L) was needed to suppress the emergence of resistance. The PTA analyses showed that adult and paediatric patients receiving a standard regimen were only successfully treated for the in vivo bactericidal target if the MIC was ≤0.125 mg/L in adults and ≤0.064 mg/L in children.

Conclusions

This study improves our understanding of teicoplanin PD against MRSA and defines an in vivo AUC/MIC target for efficacy and suppression of resistance. Additional studies are needed to further corroborate the PK/PD index in a variety of infection models and in patients.

Risk factors for hospitalizations due to bacterial respiratory tract infections after tracheotomy

OBJECTIVE

Identify characteristics associated with hospital readmission due to bacterial respiratory tract infections (bRTI) after tracheotomy.

STUDY DESIGN

Retrospective study of 8009 children 0-17 years undergoing tracheotomy from 2007 to 2013 at 48 children's hospitals in the Pediatric Health Information System database. The primary outcome was first hospital admission after tracheotomy for bRTI (ie, primary diagnosis of bRTI or a primary diagnosis of bRTI symptom and secondary diagnosis of bRTI). We used Cox-proportional hazard modeling to assess associations between patient demographic and clinical characteristics and bRTI hospital readmission.

RESULTS

Median age at tracheotomy admission was 5 months (interquartile range [IQR]: 1-50 months). Thirty-six percent (n = 2899) had at least one bRTI admission. Median time-to-readmission for bRTI was 275 days (IQR: 141-530). Factors independently associated with increased risk for bRTI readmission were younger age (eg, age < 30 days vs 13-17 years [aHR 1.32; 95%CI: 1.11-1.58]), Hispanic race/ethnicity (vs non-Hispanic White; aHR: 1.34; 95%CI: 1.20-1.50), government insurance (vs private; aHR 1.21; 95%CI: 1.10-1.33), >2 complex chronic conditions (vs zero; aHR 1.96; 95%CI: 1.34-2.86) and discharge to home (vs post-acute care setting; aHR 1.19; 95%CI: 1.08-1.32). Trauma diagnosis at tracheotomy (aHR 0.83; 95%CI: 0.69-1) and ventilator dependency (aHR 0.88; 95%CI: 0.81-0.97) were associated with decreased risk.

CONCLUSIONS

Young, Hispanic children with multiple complex chronic conditions who use Medicaid insurance and are not discharged to post-acute care are at the highest risk for hospital readmission for bRTI post-tracheotomy. Future research should investigate strategies to mitigate this risk for these children.

Length of Stay and Hospital Revisit After Bacterial Tracheostomy-Associated Respiratory Tract Infection Hospitalizations

OBJECTIVES

To identify factors associated with longer length of stay (LOS) and higher 30-day hospital revisit rates for children hospitalized with bacterial tracheostomy-associated respiratory tract infections (bTARTIs).

METHODS

This was a multicenter, retrospective cohort study using administrative data from the Pediatric Health Information System database between 2007 and 2014 of patients 30 days to 17 years old with a principal discharge diagnosis of bTARTI or a principal discharge diagnosis of bTARTI symptoms with a secondary diagnosis of bTARTI. Primary outcomes of LOS (in days) and 30-day all-cause revisit rates (inpatient, observation, or emergency department visit) were analyzed by using a 3-level hierarchical regression model (discharges within patients within hospital).

RESULTS

We included 3715 unique patients and 7355 discharges. The median LOS was 4 days (interquartile range: 3-8 days), and the 30-day revisit rate was 30.5%. Compared with children 1 to 4 years old, children aged 30 days to 12 months had both longer LOS (adjusted length of stay [aLOS] = +0.9 days; 95% confidence interval [CI]: 0.6 to 1.3) and increased hospital revisit risk (adjusted odds ratio [aOR] = 1.5; 95% CI: 1.3 to 1.7). Other factors associated with longer LOS included public insurance (aLOS = +0.5 days; 95% CI: 0.2 to 0.8), 3 or more complex chronic conditions (CCCs), mechanical ventilation (acute or chronic), and empirical anti-Pseudomonas aeruginosa antibiotics (aLOS = +0.6 days; 95% CI: 0.3 to 0.9). Other factors associated with 30-day revisit included 4 or more CCCs (aOR = 1.3; 95% CI: 1.1 to 1.6) and chronic ventilator dependency (aOR = 1.1; 95% CI: 1.0 to 1.3).

CONCLUSIONS

Ventilator-dependent patients <12 months old with at least 4 CCCs are at highest risk for both longer LOS and 30-day revisit after discharge for bTARTIs. They may benefit from bTARTI prevention strategies and intensive care coordination while hospitalized.

Interchangeability of Generic Drugs: A Nonparametric Pharmacokinetic Model of Gabapentin Generic Drugs

Substitution by generic drugs is allowed when bioequivalence to the originator drug has been established. However, it is known that similarity in exposure may not be achieved at every occasion for all individual patients when switching between formulations. The ultimate aim of our research is to investigate if pharmacokinetic subpopulations exist when subjects are exposed to bioequivalent formulations. For that purpose, we developed a pharmacokinetic model for gabapentin, based on data from a previously conducted bioavailability study comparing gabapentin exposure following administration of the gabapentin originator and three generic gabapentin formulations in healthy subjects. Both internal and external validation confirmed that the optimal model for description of the gabapentin pharmacokinetics in this comparative bioavailability study was a two‐compartment model with absorption constant, an absorption lag time, and clearance adjusted for renal function, in which each model parameter was separately estimated per administered formulation.

The effect of medication nonadherence on progression-free survival among patients with renal cell carcinoma

Objective

To examine how observed medication nonadherence to 2 second-line, oral anticancer medications (axitinib and everolimus) affects progression-free survival (PFS) among patients with renal cell carcinoma.

Methods

We used an adherence–exposure–outcome model to simulate the impact of adherence on PFS. Using a pharmacokinetic/pharmacodynamic (PK/PD) population model, we simulated drug exposure measured by area under the plasma concentration–time curve (AUC) and minimum blood or trough concentration (C_min) under 2 scenarios: 1) optimal adherence and 2) real-world adherence. Real-world adherence was measured using the medication possession ratios as calculated from health insurance claims data. A population PK/PD model was simulated on individuals drawn from the Medical Expenditure Panel Survey (MEPS), a large survey broadly representative of the US population. Finally, we used previously published PK/PD models to estimate the effect of drug exposure (i.e., C_min and AUC) on PFS outcomes under optimal and real-world adherence scenarios.

Results

Average adherence measured using medication possession ratios was 76%. After applying our simulation model to 2164 individuals in MEPS, drug exposure was significantly higher among adherent patients compared with nonadherent patients for axitinib (AUC: 249.5 vs. 159.8 ng×h/mL, P<0.001) and everolimus (AUC: 185.4 vs. 118.0 µg×h/L, P<0.001). Patient nonadherence in the real world decreased the expected PFS from an optimally adherent population by 29% for axitinib (8.4 months with optimal adherence vs. 6.0 months using real-world adherence, P<0.001) and by 5% (5.5 vs. 5.2 months, P<0.001) for everolimus.

Conclusion

Nonadherence by renal cell carcinoma patients to second-line oral therapies significantly decreased the expected PFS.

Sofosbuvir (SOF) Suppresses Ledipasvir (LDV)-resistant Mutants during SOF/LDV Combination Therapy against Genotype 1b Hepatitis C Virus (HCV)

Our objective was to identify drug interactions between ledipasvir (LDV) and sofosbuvir (SOF) against a genotype 1b replicon to determine optimal exposures for each agent that will maximize antiviral activity against susceptible and drug-resistant subpopulations. LDV and SOF were evaluated using a fully factorial experimental design in the BelloCell system. Replicon levels and drug-resistant variants were quantified at various times post-therapy for 14 days and a high-dimensional mathematical model was fit to the data. Mutations associated with SOF resistance were not detected; but LDV-resistant mutants were selected and mutant subpopulations increased as exposure intensity increased. Combination therapy was additive for the total replicon population and the LDV-resistant population, but a threshold concentration of 100 ng/ml of SOF must be attained to suppress LDV-resistant subpopulations. These novel findings hold important implications for not only improving therapeutic outcomes, but also maximizing the clinical utility of LDV and SOF combination regimens.

Pseudomonas aeruginosa and post-tracheotomy bacterial respiratory tract infection readmissions

OBJECTIVE

Identify risk factors for readmission due to a bacterial tracheostomy-associated respiratory tract infection (bTARTI) within 12 months of discharge after tracheotomy.

DESIGN/METHODS

We performed a retrospective cohort study of 240 children who underwent tracheotomy and were discharged with tracheotsomy in place between January 1, 2005 and June 30, 2013. Children with prolonged total or post-tracheotomy length of stay (LOS), less than 12 months of follow-up, or who died during the index hospitalization were excluded. Readmission for a bTARTI (eg, pneumonia, tracheitis) treated with antibiotics, as ascertained by manual chart review, was the outcome variable. We used multivariate logistic regression to identify the independent association between risk factors and hospital readmission for bTARTI within 12 months.

RESULTS

At index hospitalizations for tracheotomy, the median admission age was 5 months (interquartile range [IQR] 2-43 months) and median LOS was 73 days (IQR 43-121 days). Most patients were of Hispanic ethnicity (n = 162, 68%) and were publicly insured (n = 213, 89%). Nearly half (n = 112, 47%) were discharged on positive pressure mechanical ventilation. Many (n = 103, 43%) were admitted for bTARTI within 12 months of discharge. Only Hispanic ethnicity (adjusted odds ratio [AOR] 2.0; 95% confidence interval [CI]: 1.1-3.9; P = 0.03) and acquisition of Pseudomonas aeruginosa between tracheotomy and discharge from index hospitalization (AOR 3.2; 95%CI: 1.2-8.3; P = 0.02) were independently associated with increased odds of bTARTI readmission, while discharge on gastrointestinal pro-motility agents was associated with decreased risk (AOR = 0.4; 95%CI: 0.2-0.8; P = 0.01).

CONCLUSIONS

Hispanic ethnicity and post-tracheotomy acquisition of P. aeruginosa during initial hospitalization are associated with bTARTI readmission.

Is continuous infusion of imipenem always the best choice?

Monte Carlo simulations allow prediction and comparison of concentration-time profiles arising from different dosing regimens in a defined population, provided a population pharmacokinetic model has been established. The aims of this study were to evaluate the population pharmacokinetics of imipenem in critically ill patients with hospital-acquired pneumonia (HAP) and to assess the probability of target attainment (PTA) and cumulative fraction of response (CFR) using EUCAST data. A two-compartment model based on a data set of 19 subjects was employed. Various dosage regimens at 0.5-h and 3-h infusion rates and as continuous infusion were evaluated against the pharmacodynamic targets of 20%fT_>MIC, 40%fT_>MIC and 100%fT_>MIC. For the target of 40%fT_>MIC, all 0.5-h infusion regimens achieved optimal exposures (CFR ≥ 90%) against Escherichia coli and Staphylococcus aureus, with nearly optimal exposure against Klebsiella pneumoniae (CFR ≥ 89.4%). The 3-h infusions and continuous infusion exceeded 97% CFR against all pathogens with the exception of Pseudomonas aeruginosa and Acinetobacter spp., where the maximum CFRs were 85.5% and 88.4%, respectively. For the 100%fT_>MIC target, only continuous infusion was associated with nearly optimal exposures. Higher PTAs for the targets of 40%fT_>MIC and 100%fT_>MIC were achieved with 3-h infusions and continuous infusion in comparison with 0.5-h infusions; however, continuous infusion carries a risk of not reaching the MIC of less susceptible pathogens in a higher proportion of patients. In critically ill patients with HAP with risk factors for Gram-negative non-fermenting bacteria, maximum doses administered as extended infusions may be necessary.

Population pharmacokinetics and pharmacodynamics of teicoplanin in neonates: making better use of C-reactive protein to deliver individualized therapy

OBJECTIVES

There is uncertainty about the optimal teicoplanin regimens for neonates. The study aim was to determine the population pharmacokinetics (PK) of teicoplanin in neonates, evaluate currently recommended regimens and explore the exposure-effect relationships.

METHODS

An open-label PK study was conducted. Neonates from 26 to 44 weeks post-menstrual age were recruited (n = 18). The teicoplanin regimen was a 16 mg/kg loading dose, followed by 8 mg/kg once daily. Therapeutic drug monitoring and dose adjustment were not conducted. A standard two-compartment PK model was developed, followed by models that incorporated weight. A PK/pharmacodynamic (PD) model with C-reactive protein serial measurements as the PD input was fitted to the data. Monte Carlo simulations (n = 5000) were performed using Pmetrics. The AUCs at steady state and the proportion of patients achieving the recommended drug exposures (i.e. Cmin >15 mg/L) were determined. The study was registered in the European Clinical Trials Database Registry (EudraCT: 2012-005738-12).

RESULTS

The PK allometric model best accounted for the observed data. The PK parameters medians were: clearance = 0.435 × (weight/70)0.75 (L/h); volume = 0.765 (L); Kcp = 1.3 (h-1); and Kpc = 0.629 (h-1). The individual time-course of C-reactive protein was well described using the Bayesian posterior estimates for each patient. The simulated median AUC96-120 was 302.3 mg·h/L and the median Cmin at 120 h was 12.9 mg/L; 38.8% of patients attained a Cmin >15 mg/L by 120 h.

CONCLUSIONS

Teicoplanin population PK is highly variable in neonates, weight being the best descriptor of PK variability. A low percentage of neonates were able to achieve Cmin >15 mg/L. The routine use of therapeutic drug monitoring and improved knowledge on the PD of teicoplanin is required.

The Case for Using Higher Doses of First Line Anti-Tuberculosis Drugs to Optimize Efficacy

Apart from new anti-tuberculosis drug development, another approach for tuberculosis (TB) treatment optimization is to derive maximum benefit from current agents. However, the dosage of current anti-TB drug regimens has never been optimized according to the exposure-effect relationships of each drug. The objective of this article is to review the latest pharmacokinetic, pharmacodynamic, experimental, and clinical data concerning the use of higher doses of first-line anti-TB drugs to improve the efficacy of pulmonary tuberculosis treatment. Exposure-effect relationships have been described for all first-line anti-TB agents. There is convincing evidence that patients would benefit from higher rifamycin exposure. This could be achieved by using higher daily doses of rifampin, or more frequent dosing of rifapentine. The dose-dependent activity of pyrazinamide observed in hollow-fiber and animal models suggests that higher doses of pyrazimamide might be more efficacious, but the tolerability of such higher doses needs to be investigated in humans. It is likely that higher doses of ethambutol would be associated with higher antibacterial effect, but the dose-related ocular toxicity of the drug precludes such practice. For isoniazid, dose individualization is required to optimize patient care. The use of higher than standard doses of isoniazid in fast acetylators should result in greater early bactericidal activity. To conclude, the use of higher doses for some of the firstline anti-TB agents has definite potential for shortening or improving TB treatment.

Voriconazole pharmacokinetics following HSCT: results from the BMT CTN 0101 trial

BACKGROUND

Voriconazole is a first-line agent for the prevention and treatment of a number of invasive fungal diseases. Relatively little is known about the relationship between drug exposure and the prevention of invasive fungal infections.

PATIENTS AND METHODS

A pharmacokinetic-pharmacodynamic substudy was performed as part of the BMT CTN 0101 trial, which was a randomized clinical trial comparing voriconazole with fluconazole for the prevention of invasive fungal infections in HSCT recipients. A previously described population pharmacokinetic model was used to calculate the maximum a posteriori Bayesian estimates for 187 patients. Drug exposure in each patient was quantified in terms of the average AUC and average trough concentrations. The relationship between drug exposure and the probability of breakthrough infection was investigated using logistic regression. AUC and trough concentrations in patients with and without breakthrough infection were compared.

RESULTS

Pharmacokinetic data from each patient were readily described using the maximum a posteriori Bayesian estimates. There were only five patients that had a breakthrough infection while receiving voriconazole in the first 100 days post-HSCT. For these patients, there was no statistically significant relationship between the average AUC or average trough concentration and the probability of breakthrough infection [OR (95% CI) 1.026 (0.956-1.102) and 1.108 (0.475-2.581), respectively]. P value for these estimates was 0.474 and 0.813, respectively.

CONCLUSIONS

Given the very small number of proven/probable infections, it was difficult to identify any differences in drug exposure in HSCT recipients with and without breakthrough fungal infections.

An exploratory analysis of the ability of a cefepime trough concentration greater than 22 mg/L to predict neurotoxicity

INTRODUCTION

Cefepime trough concentrations >22 mg/L (T(>22)) have been associated with neurotoxicity in a single study.

PATIENTS AND METHODS

Neurotoxicity outcomes for 28 cefepime-treated adult patients with febrile neutropenia were abstracted from the literature. The precision of T(>22) to predict neurotoxicity was quantified using 95% confidence intervals. Thirty-two cefepime-treated patients contributed serum concentrations for a pharmacokinetic model, fit using the Nonparametric Adaptive Grid algorithm within the Pmetrics package for R. Concentration-time curves were simulated for common dosing schemes and 3 renal dispositions. Probabilities of neurotoxicity and numbers needed to harm were calculated from simulations according to the proposed pharmacokinetic/toxicodynamic threshold of T(>22). Bayesian modeling was utilized to explore other pharmacokinetic parameters relationships with neurotoxicity.

RESULTS

The mean probability of neurotoxicity at T(>22) was 51.4% (95% CI: 16.4-85.0%). Among the schemes and renal dispositions simulated, the combination of cefepime 2 g every 8 h and a creatinine clearance of 60 mL/min produced the greatest probability of neurotoxicity (48.3%). Estimated numbers needed to harm according to T(>22) ranged from 2.1 to 18.5 persons. Explorations of maximal serum concentration and area under the curve demonstrated high levels of collinearity, making it impossible to identify trough concentrations as the driver of neurotoxicity.

DISCUSSION

T(>22) had low precision as a predictive neurotoxic threshold. When a neurotoxic threshold of T(>22) was assumed, projected neurotoxicity rates and numbers needed to harm greatly exceeded observed neurotoxicity rates in the general population and in high risk subpopulations. Other drug exposure metrics should be explored.

Optimal timing of oral fosfomycin administration for pre-prostate biopsy prophylaxis

OBJECTIVES

As the optimal administration time for fosfomycin peri-procedural prophylaxis is unclear, we sought to determine optimal administration times for fosfomycin peri-procedural prophylaxis.

METHODS

Plasma, peripheral zone and transition zone fosfomycin concentrations were obtained from 26 subjects undergoing transurethral resection of the prostate (TURP), following a single oral dose of 3 g of fosfomycin. Population pharmacokinetic modelling was completed with the Nonparametric Adaptive Grid (NPAG) algorithm (Pmetrics package for R), with a four-compartment model. Plasma and tissue concentrations were simulated during the first 24 h post-dose, comparing these with EUCAST susceptibility breakpoints for Escherichia coli, a common uropathogen.

RESULTS

Non-compartmental-determined pharmacokinetic values in our population were similar to those reported in the package insert. Predicted plasma concentrations rapidly increased after the first hour, giving more than 90% population coverage for organisms with an MIC ≤4 mg/L over the first 12 h post-dose. Organisms with higher MICs fared much worse, with organisms at the EUCAST breakpoint being covered for <10% of the population at any time. Transitional zone prostate concentrations exceeded 4 mg/L for 90% of the population between hours 1 and 9. Peripheral zone prostate concentrations were much lower and only exceeded 4 mg/L for 70% of the population between hours 1 and 4.

CONCLUSIONS

Until more precise plasma and tissue data are available, we recommend that fosfomycin prophylaxis be given 1-4 h prior to prostate biopsy. We do not recommend fosfomycin prophylaxis for subjects with known organisms with MICs >4 mg/L.

Combination treatment with meropenem plus levofloxacin is synergistic against Pseudomonas aeruginosa infection in a murine model of pneumonia

BACKGROUND

Meropenem plus levofloxacin treatment was shown to be a promising combination in our in vitro hollow fiber infection model. We strove to validate this finding in a murine Pseudomonas pneumonia model.

METHODS

A dose-ranging study with meropenem and levofloxacin alone and in combination against Pseudomonas aeruginosa was performed in a granulocytopenic murine pneumonia model. Meropenem and levofloxacin were administered to partially humanize their pharmacokinetic profiles in mouse serum. Total and resistant bacterial populations were estimated after 24 hours of therapy. Pharmacokinetic profiling of both drugs was performed in plasma and epithelial lining fluid, using a population model.

RESULTS

Meropenem and levofloxacin penetrations into epithelial lining fluid were 39.3% and 64.3%, respectively. Both monotherapies demonstrated good exposure responses. An innovative combination-therapy analytic approach demonstrated that the combination was statistically significantly synergistic (α = 2.475), as was shown in the hollow fiber infection model. Bacterial resistant to levofloxacin and meropenem was seen in the control arm. Levofloxacin monotherapy selected for resistance to itself. No resistant subpopulations were observed in any combination therapy arm.

CONCLUSIONS

The combination of meropenem plus levofloxacin was synergistic, producing good bacterial kill and resistance suppression. Given the track record of safety of each agent, this combination may be worthy of clinical trial.

Individualised antibiotic dosing for patients who are critically ill: challenges and potential solutions

Infections in critically ill patients are associated with persistently poor clinical outcomes. These patients have severely altered and variable antibiotic pharmacokinetics and are infected by less susceptible pathogens. Antibiotic dosing that does not account for these features is likely to result in suboptimum outcomes. In this Review, we explore the challenges related to patients and pathogens that contribute to inadequate antibiotic dosing and discuss how to implement a process for individualised antibiotic therapy that increases the accuracy of dosing and optimises care for critically ill patients. To improve antibiotic dosing, any physiological changes in patients that could alter antibiotic concentrations should first be established; such changes include altered fluid status, changes in serum albumin concentrations and renal and hepatic function, and microvascular failure. Second, antibiotic susceptibility of pathogens should be confirmed with microbiological techniques. Data for bacterial susceptibility could then be combined with measured data for antibiotic concentrations (when available) in clinical dosing software, which uses pharmacokinetic/pharmacodynamic derived models from critically ill patients to predict accurately the dosing needs for individual patients. Individualisation of dosing could optimise antibiotic exposure and maximise effectiveness.

Inclusion of CYP3A5 genotyping in a nonparametric population model improves dosing of tacrolimus early after transplantation

Following organ engraftment, initial dosing of tacrolimus is based on recipient weight and adjusted by measured C₀ concentrations. The bioavailability and elimination of tacrolimus are affected by the patients CYP3A5 genotype. Prospective data of the clinical advantage of knowing patient's CYP3A5 genotype prior to transplantation are lacking. A nonparametric population model was developed for tacrolimus in renal transplant recipients. Data from 99 patients were used for model development and validation. A three-compartment model with first-order absorption and lag time from the dosing compartment described the data well. Clearances and volumes of distribution were allometrically scaled to body size. The final model included fat-free mass, body mass index, hematocrit, time after transplantation, and CYP3A5 genotype as covariates. The bias and imprecision were 0.35 and 1.38, respectively, in the external data set. Patients with functional CYP3A5 had 26% higher clearance and 37% lower bioavailability. Knowledge of CYP3A5 genotype provided an initial advantage, but only until 3-4 tacrolimus concentrations were known. After this, a model without CYP3A5 genotype predicted just as well. The present models seem applicable for clinical individual dose predictions but need a prospective evaluation.

Pharmacodynamics of liposomal amphotericin B and flucytosine for cryptococcal meningoencephalitis: safe and effective regimens for immunocompromised patients

BACKGROUND

Cryptococcal meningoencephalitis is a lethal infection with relatively few therapeutic options. The optimal dosage of liposomal amphotericin B (LAmB) alone or in combination with flucytosine is not known.

METHODS

A murine model of cryptococcal meningoencephalitis was used. The fungal density in the brain was determined using quantitative cultures. Pharmacokinetic-pharmacodynamic relationships were determined for LAmB and flucytosine administered alone. The effect of the combination was described using the Greco model and a mathematical model. The results were bridged to humans.

RESULTS

Inoculation resulted in hematogenous dissemination and logarithmic growth within the central nervous system. There was histological evidence of multifocal infection throughout the brain. Both LAmB and flucytosine produced a dose-dependent reduction in fungal burden. The effect of the combination of agents in the brain was additive. Bridging studies suggested that a human dosage of LAmB 3 mg/kg/d resulted in a submaximal antifungal effect. Regimens of LAmB 6 mg/kg/d alone, LAmB 3 mg/kg/d plus flucytosine 50 mg/kg/d, and LAmB 3 mg/kg/d plus flucytosine 100 mg/kg/d all resulted in near-maximal antifungal activity.

CONCLUSIONS

Potential regimens for further study in clinical trials include LAmB 6 mg/kg/d alone, LAmB 3 mg/kg/d plus flucytosine 50 mg/kg/d, and LAmB 3 mg/kg/d plus flucytosine 100 mg/kg/d.

Relevance of pharmacokinetic and pharmacodynamic modeling to clinical care of critically ill patients

Efficacious therapy is of utmost importance to save lives and prevent bacterial resistance in critically ill patients. This review summarizes pharmacokinetic (PK) and pharmacodynamic (PD) modeling methods to optimize clinical care of critically ill patients in empiric and individualized therapy. While these methods apply to all therapeutic areas, we focus on antibiotics to highlight important applications, as emergence of resistance is a significant problem. Nonparametric and parametric population PK modeling, multiple-model dosage design, Monte Carlo simulations, and Bayesian adaptive feedback control are the methods of choice to optimize therapy. Population PK can estimate between patient variability and account for potentially increased clearances and large volumes of distribution in critically ill patients. Once patient- specific PK data become available, target concentration intervention and adaptive feedback control algorithms can most precisely achieve target goals such as clinical cure of an infection or resistance prevention in stable and unstable patients with rapidly changing PK parameters. Many bacterial resistance mechanisms cause PK/PD targets for resistance prevention to be usually several-fold higher than targets for near-maximal killing. In vitro infection models such as the hollow fiber and one-compartment infection models allow one to study antibiotic-induced bacterial killing and emergence of resistance of mono- and combination therapies over clinically relevant treatment durations. Mechanism-based (and empirical) PK/PD modeling can incorporate effects of the immune system and allow one to design innovative dosage regimens and prospective validation studies. Mechanism-based modeling holds great promise to optimize mono- and combination therapy of anti-infectives and drugs from other therapeutic areas for critically ill patients.

Antiviral therapy of two patients with chromosomally-integrated human herpesvirus-6A presenting with cognitive dysfunction

BACKGROUND

Human herpesvirus 6 (HHV-6) is a neurotropic virus implicated in central nervous system (CNS) dysfunction, multiple sclerosis, seizures and encephalitis. Inherited or "chromosomally integrated" HHV-6 (CIHHV-6) is a condition characterized by high DNA loads and germ line transmission of HHV-6 genomes, which are integrated into the telomere.

OBJECTIVES

We previously reported that integrated HHV-6 can be reactivated by trichostatin A in vitro. Therefore, we hypothesized that a broad array of neurological symptoms of CIHHV-6 patients may respond to antiviral drug treatment.

STUDY DESIGN

The patients have been treated with antiviral drugs and monitored for viral load, late mRNA, and clinical improvement.

RESULTS

Antiviral therapy of two CIHHV patients resulted in successful clinical resolution. However, both patients relapsed on multiple occasions within 4-6 months of cessation of antiviral therapy.

CONCLUSIONS

Successful antiviral drug treatment suggests that clinical symptoms of these patients were due to symptomatic reactivation of CIHHV-6. Alternatively, some CIHHV-6 patients may have a reduced resistance to community-acquired HHV-6 strains due to tolerance leading to persistent infections.

More codeine fatalities after tonsillectomy in North American children

In 2009 we reported the fatal case of a toddler who had received codeine after adenotonsillectomy for obstructive sleep apnea syndrome. The child was an ultra-rapid metabolizer of cytochrome P4502D6 (CYP2D6). We now report 3 additional fatal or life-threatening cases from North America. In the 2 fatal cases, functional gene duplications encoding for CYP2D6 caused a significantly greater production of potent morphine from its parent drug, codeine. A severe case of respiratory depression in an extensive metabolizer is also noted. These cases demonstrate that analgesia with codeine or other opioids that use the CYP2D6 pathway after adenotonsillectomy may not be safe in young children with obstructive sleep apnea syndrome.

Safety and efficacy of CMX001 as salvage therapy for severe adenovirus infections in immunocompromised patients

No therapeutic agent has yet been established as the definitive therapy for adenovirus infections. We describe the clinical experience of 13 immunocompromised patients who received CMX001 (hexadecyloxypropyl cidofovir), an orally bioavailable lipid conjugate of cidofovir, for adenovirus disease. We retrospectively analyzed 13 patients with adenovirus disease and viremia treated with CMX001; data were available for ≥ 4 weeks after initiation of CMX001 therapy. Virologic response (VR) was defined as a 99% drop from baseline or undetectable adenovirus DNA in serum. The median age of the group was 6 years (range, 0.92-66 years). One patient had severe combined immunodeficiency, 1 patient was a small bowel transplant recipient, and 11 were allogeneic stem cell transplant recipients. Adenovirus disease was diagnosed at a median of 75 days (range, 15-720 days) after transplantation. All patients received i.v. cidofovir for a median of 21 days (range, 5-90 days) before CMX001 therapy. The median absolute lymphocyte count at CMX001 initiation was 300 cells/μL (range, 7-1500 cells/μL). Eight patients (61.5%) had a ≥ 1 log10 drop in viral load after the first week of therapy. By week 8, 9 patients (69.2%) demonstrated a VR, with a median time to achieve VR of 7 days (range, 3-35 days). The change in absolute lymphocyte count was inversely correlated with the change in log10 viral load only at week 6 (r = -0.74; P = .03). Patients with VR had longer survival than those without VR (median 196 days versus 54.5 days; P = .04). No serious adverse events were attributed to CMX001 during therapy. CMX001 may be a promising therapeutic option for the treatment of severe adenovirus disease in immunocompromised patients.

Cervical shedding of HIV-1 RNA among women with low levels of viremia while receiving highly active antiretroviral therapy

BACKGROUND

Among women with low or undetectable quantities of HIV-1 RNA in plasma, factors associated with genital HIV-1 RNA shedding, including choice of treatment regimen, are poorly characterized.

METHODS

We measured HIV-1 RNA in cervical swab specimens obtained from participants in the Women's Interagency HIV Study who had concurrent plasma viral RNA levels <500 copies/mL, and we assessed factors associated with genital HIV shedding. The study was powered to determine the relative effects of antiretroviral protease inhibitors (PIs) versus nonnucleoside reverse transcriptase inhibitors (NNRTIs) on viral RNA shedding.

RESULTS

Overall, 44 (15%) of 290 women had detectable HIV-1 RNA in cervical specimens. In the final multivariate model, shedding was independently associated with NNRTI (vs. PI) use (odds ratio [OR], 95% confidence interval [CI]: 2.24, 1.13 to 4.45) and illicit drug use (OR, 95% CI: 2.41, 0.96 to 5.69).

CONCLUSIONS

This is the largest study to define risks for genital HIV-1 RNA shedding in women with low/undetectable plasma virus. Shedding in this population was common, and NNRTI-based highly active antiretroviral therapy (HAART) (vs. PI-based HAART) was associated with genital HIV shedding. Further study is required to determine the impact of these findings on transmission of HIV from mother to child or to sexual partners.

Pharmacokinetics, safety, and tolerability of caspofungin in children and adolescents

Caspofungin is a parenteral antifungal that inhibits beta-1,3-D-glucan synthesis. Although licensed for adult use, the appropriate caspofungin dosing regimen in pediatric patients is not yet known. We therefore investigated the pharmacokinetics and safety of caspofungin in pediatric patients. Thirty-nine children (ages 2 to 11 years) and adolescents (ages 12 to 17 years) with neutropenia were administered caspofungin using either a weight-based regimen (1 mg/kg of body weight/day) or a body surface area regimen (50 mg/m2/day or 70 mg/m2/day). Plasma samples for caspofungin profiles were collected on days 1 and 4. These results were compared to those from adults treated with either 50 or 70 mg/day for mucosal candidiasis. In children receiving 1 mg/kg/day (maximum, 50 mg/day), the area under the concentration-time curve over 24 h (AUC(0-24)) was significantly smaller (46% after multiple doses) than that observed in adults receiving 50 mg/day (P < 0.001). In children and adolescents receiving 50 mg/m2/day (maximum, 70 mg/day), the AUC(0-24) following multiple doses was similar to that for the exposure in adults receiving 50 mg/day. The AUC(0-24) and concentration trough (at 24 h) in pediatric patients receiving the 50-mg/m2 daily regimen were consistent across the range of ages. Caspofungin was generally well tolerated in this study. None of the patients developed a serious drug-related adverse event or were discontinued for toxicity. These results demonstrate that caspofungin at 1 mg/kg/day in pediatric patients is suboptimal. Caspofungin administration at 50 mg/m2/day provides a comparable exposure to that of adult patients treated with 50 mg/day.

Role for a phage promoter in Shiga toxin 2 expression from a pathogenic Escherichia coli strain

Shiga toxins (Stxs), encoded by the stxA and stxB genes, are important contributors to the virulence of Escherichia coli O157:H7 and other Stx-producing E. coli (STEC) strains. The stxA and stxB genes in STEC strains are located on the genomes of resident prophages of the lambda family immediately downstream of the phage late promoters (p(R')). The phage-encoded Q proteins modify RNA polymerase initiating transcription at the cognate p(R') promoter which creates transcription complexes that transcend a transcription terminator immediately downstream of p(R') as well as terminator kilobases distal to p(R'). To test if this Q-directed processive transcription plays a role in stx(2)AB expression, we constructed a mutant prophage in an O157:H7 clinical isolate from which p(R') and part of Q were deleted but which has an intact pStx, the previously described stx(2)AB-associated promoter. We report that production of significant levels of Stx2 in this O157:H7 isolate depends on the p(R') promoter. Since transcription initiating at p(R') ultimately requires activation of the phage lytic cascade, expression of stx(2)AB in STEC depends primarily on prophage induction. By showing this central role for the prophage in stx(2)AB expression, our findings contradict the prevailing assumption that phages serve merely as agents for virulence gene transfer.

The exciting future of antifungal therapy

Invasive fungal infections are becoming more common. Current therapy is generally limited to amphotericin B in its parent and lipid formulations, 5-fluctyosine, fluconazole, and itraconazole. Toxicity, drug-drug interactions, and increasing fungal resistance reduce the usefulness of these drugs, and the need for new therapies is pressing. This article briefly discusses the limitations of antifungal minimum inhibitory testing, and then summarizes new antifungal drugs in development that have been tested in humans. It also addresses novel treatment strategies such as drug combination therapy, pharmacological reformulations to improve the efficacy or reduce the toxicity of current antifungal drugs, immune function augmentation, and vaccine development. All of these strategies, although in their infancy, will enhance the clinician's ability to care for patients with invasive fungal infections.

N-mediated transcription antitermination in lambdoid phage H-19B is characterized by alternative NUT RNA structures and a reduced requirement for host factors

Gene expression in lambdoid phages in part is controlled by transcription antitermination. For most lambdoid phages, maximal expression of delayed early genes requires an RNA polymerase modified by the phage N and host Nus proteins at RNA NUT sites. The NUT sites (NUTL and NUTR) are made up of three elements: BOXA, BOXB and an intervening spacer sequence. We report on N antitermination in H-19B, a lambdoid phage carrying shiga toxin 1 genes. H-19B N requires NusA, but not two other host factors required by lambda N, NusB and ribosomal protein S10. The H-19B NUT site BOXA is not required, whereas the BOXB is required for N action. H-19B nut sites have dyad symmetries in the spacer regions that are not in other nut sites. Changes in one arm of the dyad symmetry inactivate the NUT RNA. Compensating changes increasing the number of mutant nucleotides but restoring dyad symmetry restore activity. Deletion of the sequences encoding the dyad symmetry has little effect. Thus, the specific nucleotides composing the dyad symmetry seem relatively unimportant. We propose that the RNA stem-loop structure, called the 'reducer', by sequestering nucleotides from the linear RNA brings into proximity sites on either side of the dyad symmetry that contribute to forming an active NUT site.