Population pharmacokinetics of cefazolin in critically ill children infected with methicillin-sensitive Staphylococcus aureus

ObjectivesCefazolin is one of curative treatments for infections due to methicillin-sensitive Staphylococcus aureus (MSSA). Both growth and critical illness may impact the pharmacokinetic (PK) parameters. We aimed to build a population PK model for cefazolin in critically ill children in order to optimize individual dosing regimens.MethodsWe included all children (age < 18 years, body weight (BW) > 2.5 kg) receiving cefazolin for MSSA infection. Cefazolin total plasma concentrations were quantified by high-performance liquid chromatography. A data modelling process was performed with the software MONOLIX. Monte Carlo simulations were used in order to attain the PK target of 100% fT _{> 4 × MIC}.ResultsThirty-nine patients with a median (range) age of 7 (0.1–17) years and a BW of 21 (2.8–79) kg were included. The PK was ascribed to a one-compartment model, where typical clearance and volume of distribution estimations were 1.4 L/h and 3.3 L respectively. BW, according to the allometric rules, and estimated glomerular filtration rate (eGFR) on clearance were the two influential covariates. Continuous infusion with a dosing of 100 mg/kg/day to increase to 150 mg/kg/day for children with a BW < 10 kg or eGFR >200 mL/min/1.73m² were the best schemes to reach the PK target of 100% fT _{> 4 × MIC}.ConclusionsIn critically ill children infected with MSSA, continuous infusion seems to be the most appropriate scheme to reach the PK target of 100 % fT _{> 4 × MIC} in children with normal and augmented renal function.     

Pharmacokinetics and pharmacodynamics of ciprofloxacin in critically ill patients after the first intravenous administration of 400 mg

PurposeTo investigate the pharmacokinetics and pharmacodynamics of ciprofloxacin in critically ill patients after the first intravenous administration of 400 mg.Material/methods.Plasma concentrations were measured in 20 critically ill patients (mean [SD]; age, 55.5 [16.5] years; weight, 80.3 [16.9] kg; and creatinine clearance, 110.0 [71.5] mL/min). Four blood samples were drawn at the following time points 0, 0.5, 6, 8 hours after infusion. Ciprofloxacin concentrations were determined by high-performance liquid chromatography. Results. In the cases where ciprofloxacin was applied in targeted antibiotic therapy the minimum inhibitory concentrations (MIC) were ≤0.5 mg/l. The maximum and minimum plasma concentrations of ciprofloxacin were 1.74 (0.58-7.90) and 0.45 (0.16-2.96) mg/l, respectively. The main pharmacokinetic parameters for ciprofloxacin in the analyzed patients were as follows: k_el, 0.21 h^?1; t_1/2kel, 3.37 h; AUC_0-inf, 10.10 mg×h/l; AUMC_0-last, 15.36 mg×h²/l; MRT, 1.71 h; V_d, 214.8 l; Cl, 39.70 l/h. Considering the maximum value of MIC (0.5 mg/l) only 30% and 25% of analyzed patients had desired values of the PK/PD indexes AUIC>125 and C_max /MIC>10, respectively.Conclusions.The target plasma concentrations after the first dose of ciprofloxacin were reached only in a few critically ill patients. Considerable inter-subject variability for PK/PD parameters in ICU patients requires systematic monitoring.     

The effects of different doses of inhaled bacteriophage therapy for Pseudomonas aeruginosa pulmonary infections in mice

ObjectivesInhaled phage therapy has been revisited as a potential treatment option for respiratory infections caused by multidrug-resistant Pseudomonas aeruginosa; however, there is a distinct gap in understanding the dose–response effect. The aim of this study was to investigate the dose–response effect of Pseudomonas-targeting phage PEV31 delivered by the pulmonary route in a mouse lung infection model.MethodsNeutropenic BALB/c mice were infected with multidrug-resistant P. aeruginosa (2 × 10⁴ colony-forming units) through the intratracheal route and then treated with PEV31 at three different doses of 7.5 × 10⁴ (Group A), 5 × 10⁶ (Group B), and 5 × 10⁸ (Group C) plaque-forming units, or phosphate-buffered saline at 2 hours postinoculation. Mice (n = 5–7) were euthanized at 2 hours and 24 hours postinfection, and lungs, kidneys, spleen, liver, bronchoalveolar lavage fluid, and blood were collected for bacteria and phage enumeration.ResultsAt 24 hours postinfection, all phage-treated groups exhibited a significant reduction in pulmonary bacterial load by 1.3–1.9 log₁₀, independent of the delivered phage dose. The extent of phage replication was negatively correlated with the dose administered, with log₁₀ titre increases of 6.2, 2.7, and 9 for Groups A, B, and C, respectively. Phage-resistant bacterial subpopulations in the lung homogenate samples harvested at 24 hours postinfection increased with the treatment dose (i.e. 30%, 74%, and 91% in respective Groups A–C). However, the mutants showed increased susceptibility to ciprofloxacin, impaired twitching motility, and reduced blue-green pigment production. The expression of the inflammatory cytokines (IL-1ß and IL-6, and TNF-α) was suppressed with increasing PEV31 treatment dose.DiscussionThis study provides the dose–response effect of inhaled phage therapy that may guide dose selection for treating P. aeruginosa respiratory infections in humans.     

Population pharmacokinetic and pharmacodynamic modeling of norvancomycin

In this paper, population pharmacokinetics (PPK) and pharmacodynamics of norvancomycin in patients were investigated. The studied dataset was derived from 146 patients with confirmed or suspected gram-positive bacterial infections, as well as 20 healthy volunteers. A PPK model was developed and validated by the nonlinear mixed effect model (NONMEM) software. The norvancomycin minimum inhibitory concentrations (MICs) for the isolates from patients were determined by the agar dilution method. The best model was a two-compartment pharmacokinetic model with exponential inter-individual error and an additive residual error statistic model. The findings of the present study indicated that the change in CLcr values had different effects on drug clearance (CL). In patients with renal dysfunction (CLcr≤85 ml/min), CL (L/h)=2.54·(CLcr /50)^1.20, while in patients with normal renal function (CLcr>85 ml/min), CL=6.0·(WT/60)^0.52. An increased volume of peripheral distribution (V₂) was observed when norvancomycin was co-administered with diuretics. Inter-individual variability in CL, V₁, Q, and V₂ was 35.92%, 11.40%, 0, and 79.75%, respectively. Residual variability was 3.05 mg/L. The logistic stepwise analyses revealed that only the ratio of AUC₂₄ /MIC was a major factor which could significantly predict the clinical outcome and bacterial eradication in patients. As the AUC₂₄/MIC ratio was >579.90 for staphylococcal infection and >637.67 for enterococcal infections, approximately 95% of patients would be predicted to achieve a cured clinical outcome. In conclusion, AUC₂₄/MIC should be a major pharmacokinetics/pharmacodynamics (PK/PD) parameter to predict the clinical efficacy of norvancomycin. An optimized regimen of norvancomycin can be simulated and developed for different subgroups of patients who have special physiologic and pathologic conditions.     

Translational in vitro and in vivo PKPD modelling for apramycin against Gram-negative lung pathogens to facilitate prediction of human efficacious dose in pneumonia

ObjectivesNew drugs and methods to efficiently fight carbapenem-resistant gram-negative pathogens are sorely needed. In this study, we characterized the preclinical pharmacokinetics (PK) and pharmacodynamics of the clinical stage drug candidate apramycin in time kill and mouse lung infection models. Based on in vitro and in vivo data, we developed a mathematical model to predict human efficacy.MethodsThree pneumonia-inducing gram-negative species Acinetobacter baumannii, Pseudomonas aeruginosa, and Klebsiella pneumoniae were studied. Bactericidal kinetics were evaluated with time-kill curves; in vivo PK were studied in healthy and infected mice, with sampling in plasma and epithelial lining fluid after subcutaneous administration; in vivo efficacy was measured in a neutropenic mouse pneumonia model. A pharmacokinetic-pharmacodynamic model, integrating all the data, was developed and simulations were performed.ResultsGood lung penetration of apramycin in epithelial lining fluid (ELF) was shown (area under the curve (AUC)_ELF/AUC_plasma = 88%). Plasma clearance was 48% lower in lung infected mice compared to healthy mice. For two out of five strains studied, a delay in growth (～5 h) was observed in vivo but not in vitro. The mathematical model enabled integration of lung PK to drive mouse PK and pharmacodynamics. Simulations predicted that 30 mg/kg of apramycin once daily would result in bacteriostasis in patients.DiscussionApramycin is a candidate for treatment of carbapenem-resistant gram-negative pneumonia as demonstrated in an integrated modeling framework for three bacterial species. We show that mathematical modelling is a useful tool for simultaneous inclusion of multiple data sources, notably plasma and lung in vivo PK and simulation of expected scenarios in a clinical setting, notably lung infections.     

A model-based analysis of pharmacokinetic–pharmacodynamic (PK/PD) indices of avibactam against Pseudomonas aeruginosa

ObjectiveThe aim of the present work was to use a semi-mechanistic pharmacokinetic–pharmacodynamic (PK/PD) model developed from in vitro time–kill measurements with P. aeruginosa to compare different pharmacodynamic indices derived from simulated human avibactam exposures, with respect to their degree of correlation with the modelled bacterial responses.MethodsA mathematical model of the effect of ceftazidime–avibactam on the growth dynamics of P. aeruginosa was used to simulate bacterial responses to modelled human exposures from fractionated avibactam dosing regimens with a fixed ceftazidime dosing regimen (2 or 8 g q8h as a 2-h infusion). The relatedness of the 24-h change in bacterial density and avibactam exposure parameters was evaluated to determine exposure parameter that closely correlated with bacterial growth/killing responses.ResultsFrequent dosing was associated with higher efficacy, resulting in a reduction of avibactam daily dose. The best-fit PD index of avibactam determined from the simulation was fT > C_T of 1 mg/L avibactam and q8h was the longest dosing interval able to achieve 2-log kill: 41–87% (3.3 h to 7.0 h out of 8-h interval, respectively). The avibactam exposure magnitude required to achieve a 2-log kill in the simulations was dependent on the susceptibility of the bacterial isolate to ceftazidime.ConclusionsAvibactam activity in combination with ceftazidime against multidrug resistant P. aeruginosa correlated with fT > C_T. Setting a threshold avibactam concentration to 1 mg/L, superimposed over a simulated human-like exposure of ceftazidime, achieved at least 2-log kill for the clinical dose of 500 mg q8h avibactam as a 2-h infusion, depending on the minimum inhibitory concentration of ceftazidime alone.     

Pharmacokinetic analysis of nevirapine extended release 400 mg once daily vs nevirapine immediate release 200 mg twice daily formulation in treatment-naïve patients with HIV-1 infection

Background: VERxVE data showed non-inferior virologic efficacy with extended release nevirapine (NVP-XR) dosed 400 mg once daily (QD) versus immediate release nevirapine (NVP-IR) 200 mg twice daily in a double-blind, non-inferiority study in treatment-naïve HIV-1-positive patients.

Objective: To study the pharmacokinetics (PK) of the NVP formulations and identify possible associations with demographic factors.

Methods: Patients with viral load ≥1000 copies/mL and CD4+ count > 50– <400 cells/mm³ (males) and >50– <250 cells/mm³ (females) at screening received NVP-IR 200 mg QD during a 14-day lead-in and were then stratified by baseline viral load and randomized to NVP-XR or -IR. NVP trough concentrations at steady state (SS) (C_pre,ss,N) were measured up to week 48 for all participating patients. In a PK sub-study, SS parameters – AUC_0–24, C_max, C_min, and peak-to-trough fluctuation were obtained and analyzed with relative bioavailability assessed at week 4 by plasma collection over 24 h.

Results: Trough concentrations were stable from week 4 to week 48 for all patients (n = 1011) with both formulations, with NVP-XR/IR ratios of 0.77–0.82. Overall, 49 patients completed the PK sub-study: 24 XR and 25 IR. NVP-XR showed less peak-to-trough fluctuation (34.5%) than IR (55.2%), and lower AUC_0–24, C_min, C_max, and trough concentrations than IR. However, no effect of SS trough concentrations was found on the virologic response proportion at least up to 1000 ng/mL. No significant association was found between NVP PK and gender, race, and viral load.

Conclusion: These data suggest NVP-XR achieves lower but effective NVP exposure compared with NVP-IR.     

Using machine learning to optimize antibiotic combinations: dosing strategies for meropenem and polymyxin B against carbapenem-resistant Acinetobacter baumannii

ObjectivesIncreased rates of carbapenem-resistant strains of Acinetobacter baumannii have forced clinicians to rely upon last-line agents, such as the polymyxins, or empirical, unoptimized combination therapy. Therefore, the objectives of this study were: (a) to evaluate the in vitro pharmacodynamics of meropenem and polymyxin B (PMB) combinations against A. baumannii; (b) to utilize a mechanism-based mathematical model to quantify bacterial killing; and (c) to develop a genetic algorithm (GA) to define optimal dosing strategies for meropenem and PMB.MethodsA. baumannii (N16870; MIC_meropenem = 16 mg/L, MIC_PMB = 0.5 mg/L) was studied in the hollow-fibre infection model (initial inoculum 10⁸ cfu/mL) over 14 days against meropenem and PMB combinations. A mechanism-based model of the data and population pharmacokinetics of each drug were used to develop a GA to define the optimal regimen parameters.ResultsMonotherapies resulted in regrowth to ~10¹⁰ cfu/mL by 24 h, while combination regimens employing high-intensity PMB exposure achieved complete bacterial eradication (0 cfu/mL) by 336 h. The mechanism-based model demonstrated an SC₅₀ (PMB concentration for 50% of maximum synergy on meropenem killing) of 0.0927 mg/L for PMB-susceptible subpopulations versus 3.40 mg/L for PMB-resistant subpopulations. The GA had a preference for meropenem regimens that improved the %T > MIC via longer infusion times and shorter dosing intervals. The GA predicted that treating 90% of simulated subjects harbouring a 10⁸ cfu/mL starting inoculum to a point of 10⁰ cfu/mL would require a regimen of meropenem 19.6 g/day 2 h prolonged infusion (2 hPI) q5h + PMB 5.17 mg/kg/day 2 hPI q6h (where the 0 h meropenem and PMB doses should be ‘loaded’ with 80.5% and 42.2% of the daily dose, respectively).ConclusionThis study provides a methodology leveraging in vitro experimental data, a mathematical pharmacodynamic model, and population pharmacokinetics provide a possible avenue to optimize treatment regimens beyond the use of the ‘traditional’ indices of antibiotic action.     

Validity of the Oxycon Mobile metabolic system under field measuring conditions

Abstract  

This study aimed to validate a portable metabolic system in field measuring conditions, such as prolonged moderate exercise at low temperatures, high humidity and with external wind. VO₂, VCO₂, RER and V _E were measured using the Oxycon Mobile (OM), with a windshield, during cycle ergometer exercise: (1) indoors at three submaximal workloads with no wind or with external wind (13–20 m s⁻¹) from front, side and back; (2) at two submaximal workloads outdoors (12 ± 2°C; 86 ± 7% relative humidity (RH)), with and without a system for drying the ambient air around the air sampling tube; and (3) at one workload outdoors for 45 min (5 ± 4°C; 69 ± 16.5% RH). Any physiological drift was checked for with pre- and postmeasurements by the Douglas bag method (DBM). A minor effect of external wind from behind was noted in RER and V _E (−2 and −3%). The system for drying the ambient air around the gas sampling tube had no effect on the measured levels. A small difference in VCO₂ drift between the OM and DBM (1.5 mL min⁻²) was noted in the stability test. The results indicated that heavy external wind applied from different directions generally does not affect the measurements of the OM and further that, when using a unit for drying the ambient air around the gas sampling tube, the OM can accurately measure VO₂, RER and V _E at submaximal workloads for at least 45 min under challenging conditions with regard to humidity and temperature.     

Cefepime population pharmacokinetics and dosing regimen optimization in critically ill children with different renal function

ObjectiveCefepime is commonly used in pediatric intensive care units, where unpredictable variations in the patients' pharmacokinetic (PK) variables may require drug dose adjustments. The objectives of the present study were to build a population PK model for cefepime in critically ill children and to optimize individual initial dosing regimens.MethodsChildren (aged from 1 month to 18 years; body weight >3 kg) receiving cefepime were included. Cefepime total plasma concentrations were measured using high performance liquid chromatography. Data were modelled using nonlinear, mixed-effect modeling software, and Monte Carlo simulations were performed with a PK target of 100% fT _{> MIC}.ResultsFifty-nine patients (median (range) age: 13.5 months (1.1 months to 17.6 years)) and 129 cefepime concentration measurements were included. The cefepime concentration data were best fitted by a one-compartment model. The selected covariates were body weight with allometric scaling and estimated glomerular filtration rate on clearance. Mean population values for clearance and volume were 1.21 L/h and 4.8 L, respectively. According to the simulations, a regimen of 100 mg/kg/d q12 h over 30 min or 100 mg/kg/d as a continuous infusion was more likely to achieve the PK target in patients with renal failure and in patients with normal or augmented renal clearance, respectively.DiscussionAppropriate cefepime dosing regimens should take renal function into account. Continuous infusions are required in critically ill children with normal or augmented renal clearance, while intermittent infusions are adequate for children with acute renal failure. Close therapeutic drug monitoring is mandatory, given cefepime's narrow therapeutic window.     

Comparative effectiveness of dried plasma HIV-1 viral load testing in Brazil using ViveST for sample collection

BackgroundUtilization of dried plasma for HIV-1 viral load testing would significantly decrease sample shipping costs.ObjectivesTo describe the precision and reproducibility of ViveST^® (ST) as a transportation method for shipping specimens for HIV-1 viral load (VL) testing.Study designThirty clinical plasma samples were used to generate replicate samples with HIV VL values of 4 log₁₀, 3 log₁₀ and 2 log₁₀ copies/mL for reproducibility testing and an additional 299 samples with HIV VL <50 copies/mL (99); 1.7 log₁₀ to 3.99 log₁₀ (100); and 4 log₁₀ to 5.99 log₁₀/mL (100) were used to compare ViveST to frozen plasma samples using the VERSANT^® HIV-1 RNA 3.0 Assay. Results were compared using Student t-test, Pearson correlation and Bland–Altman analyses.ResultsMean intra-assay variance among frozen and dried plasma triplicates was 0.15 log₁₀ and 0.09 log₁₀ copies/mL respectively (n = 10, P = NS). Compared to frozen plasma, there was a mean reduction of 0.3 log₁₀, 0.27 log₁₀, and 0.35 log₁₀ copies/mL at the 4 log₁₀, 3 log₁₀, and 2 log₁₀ copy/mL samples respectively (n = 30, all comparisons, P < 0.01). Overall correlation between 299 frozen and ViveST samples was r = 0.97, where 12 of 99 undetectable frozen VL were positive with ST, and 12 of 200 frozen detectable VL were undetectable with ViveST (mean VL 2.1, 1.9 log₁₀ copies/mL respectively).ConclusionsHIV-1 viral load results using ViveST were reproducible, correlated well with frozen plasma, though yielding minimally lower values. Our data suggest that dried plasma for HIV-1 VL testing using ViveST has promise for use in HIV clinical practice.     

Effect of omalizumab on lung function and eosinophil levels in adolescents with moderate-to-severe allergic asthma

BackgroundOmalizumab improves clinical outcomes in patients with asthma. Several studies have shown lung function improvements with omalizumab; however, this has not been examined exclusively in adolescents.ObjectiveTo assess the effect of omalizumab on lung function and eosinophil counts in adolescents with uncontrolled moderate-to-severe allergic asthma.MethodsIn this post hoc analysis, data from adolescents aged 12 to 17 years from 8 randomized trials of omalizumab were pooled (studies 008, 009, and 011, and SOLAR, INNOVATE, ALTO, ETOPA, and EXTRA). Changes from baseline to end of study in forced expiratory volume in 1 second (FEV₁), percent predicted FEV₁ (ppFEV₁), forced vital capacity (FVC), and blood eosinophil counts were assessed by fitting an analysis of covariance model and calculating least squares mean (LSM) difference for omalizumab vs placebo.ResultsA total of 340 adolescents were identified (omalizumab, n = 203 [59.7%]; placebo, n = 137 [40.3%]). Omalizumab increased all baseline lung function variables more than placebo by end of study: LSM treatment differences (95% confidence interval) were 3.0% (0.2%-5.7%; P = .035), 120.9 mL (30.6-211.2 mL; P = .009), and 101.5 mL (8.3-194.6 mL; P = .033) for ppFEV₁, absolute FEV₁, and FVC, respectively. The LSM difference demonstrated a greater reduction in eosinophil counts for omalizumab vs placebo: −85.9 cells/μL (−137.1 to −34.6 cells/μL; P = .001).ConclusionOmalizumab was associated with lung function improvements and circulating eosinophil counts reductions in adolescents with moderate-to-severe uncontrolled asthma. Findings emphasize the effect of omalizumab in young patients and the need to optimize treatment early in the disease course. https://clinicaltrials.gov/: NCT00314574, NCT00046748, NCT00401596     

In vivo evaluation of safety and efficacy of self-assembled nanoparticles for oral insulin delivery

A variety of approaches have been studied in the past to overcome the problems encountered with the oral delivery of insulin, but with little success. In this study, self-assembled nanoparticles (NPs) with a pH-sensitive characteristic were prepared by mixing the anionic poly-γ-glutamic acid solution with the cationic chitosan solution in the presence of MgSO₄ and sodium tripolyphosphate. The in vitro results found that the transport of insulin across Caco-2 cell monolayers by NPs appeared to be pH-dependent; with increasing pH, the amount of insulin transported decreased significantly. An in vivo toxicity study was performed to establish the safety of the prepared NPs after oral administration. Additionally, the impact of orally administered NPs on the pharmacodynamics (PD) and pharmacokinetics (PK) of insulin was evaluated in a diabetic rat model. The in vivo results indicated that the prepared NPs could effectively adhere on the mucosal surface and their constituted components were able to infiltrate into the mucosal cell membrane. The toxicity study indicated that the NPs were well tolerated even at a dose 18 times higher than that used in the PD/PK study. Oral administration of insulin-loaded NPs demonstrated a significant hypoglycemic action for at least 10 h in diabetic rats and the corresponding relative bioavailability of insulin was found to be 15.1 ± 0.9%. These findings suggest that the NPs prepared in the study are a promising vehicle for oral delivery of insulin.     

The exercise dose affects oxidative stress and brachial artery flow-mediated dilation in trained men

The aim of this investigation was to establish whether changes in oxidative stress and endothelial function following acute aerobic exercise are dose-dependent. Ten healthy trained men completed four exercise sessions: 50% VO_2peak for 30 min (moderate intensity moderate duration, MIMD), 50% VO_2peak for 60 min (moderate intensity long duration, MILD), 80% VO_2peak for 30 min (high intensity moderate duration, HIMD), and 80% VO_2peak for the time to reach the caloric equivalent of MIMD (high intensity short duration, HISD). Thiobarbituric acid reactive substances (TBARS) were measured as an index of oxidative stress and brachial artery flow-mediated dilation (FMD) was assessed as an index of endothelial function. Variables were measured at baseline, immediately post-exercise, 1 and 2 h post-exercise. Both HIMD (14.2 ± 2.5 μmol/L) and HISD (14.7 ± 1.9 μmol/L) TBARS differed from MIMD (11.8 ± 1.5 μmol/L) immediately post-exercise. TBARS increased from pre to immediately post-exercise for HIMD (12.6 ± 2.1 vs.14.2 ± 2.5 μmol/L) and HISD (12.3 ± 2.8 vs. 14.7 ± 1.9 μmol/L). Both MIMD (7.2 ± 2.2%) and HISD (7.6 ± 2.7%) FMD immediately post-exercise were greater than HIMD (4.7 ± 2.2%). An increase of FMD from pre to immediately post-exercise was found for MIMD (5.0 ± 2.5 vs. 7.2 ± 2.2%) and HISD (5.9 ± 2.4 vs. 7.6 ± 2.7%). These data suggest that acute exercise-induced TBARS are exercise intensity-dependent whereas FMD appears to improve following energy expenditure equivalent to 30 min 50% VO_2peak, regardless of intensity or duration.     

Dalbavancin exposure in vitro selects for dalbavancin-non-susceptible and vancomycin-intermediate strains of methicillin-resistant Staphylococcus aureus

ObjectivesDalbavancin is a lipoglycopeptide active against methicillin-resistant Staphylococcus aureus (MRSA). Its long half-life (8.5–16 days) allows for once-weekly or single-dose treatments but could prolong the mutant selection window, promoting resistance and cross-resistance to related antimicrobials such as vancomycin. The objective of this study was to evaluate the capacity of post-distributional pharmacokinetic exposures of dalbavancin to select for resistance and cross-resistance in MRSA.MethodsWe simulated average, post-distributional exposures of single-dose (1500 mg) dalbavancin (fCmax 9.9 μg/mL, β-elimination t_1/2 204 h) in an in vitro pharmacokinetic/pharmacodynamic (PK/PD) model for 28 days (672 h) against five MRSA strains and one methicillin-susceptible strain (MSSA). Samples were collected at least daily, and surviving colonies were enumerated and screened for resistance on drug-free and dalbavancin-supplemented medium respectively. Isolates from resistance screening plates were subjected to whole-genome sequencing (WGS) and susceptibly testing against dalbavancin, vancomycin, daptomycin, and six β-lactams with varying penicillin-binding protein (PBP) affinities.ResultsDalbavancin was bactericidal against most strains for days 1–4 before regrowth of less susceptible subpopulations occurred. Isolates with eight-fold increases in dalbavancin MIC were detected as early as day 4 but increased 64–128-fold in all models by day 28. Vancomycin and daptomycin MICs increased 4–16-fold, exceeding the susceptibly breakpoints for both antibiotics; β-lactam MICs generally decreased by two-to eight-fold, suggesting a dalbavancin–β-lactam seesaw effect, but increased by eight-fold or more in certain isolates. Resistant isolates carried mutations in a variety of genes, most commonly walKR, apt, stp1, and atl.ConclusionsIn our in vitro system, post-distributional dalbavancin exposures selected for stable mutants with reduced susceptibility to dalbavancin, vancomycin, and daptomycin, and generally increased susceptibility to β-lactams in all strains of MRSA tested. The clinical significance of these findings remains unclear, but created an opportunity to genotype a unique collection of dalbavancin-resistant strains for the first time. Mutations involved genes previously associated with vancomycin intermediate susceptibility and daptomycin non-susceptibility, most commonly walKR-associated genes.     

Non-invasive haemodynamic assessments using Innocor™ during standard graded exercise tests

Cardiac output (Q) and stroke volume (V _S) represent primary determinants of cardiovascular performance and should therefore be determined for performance diagnostics purposes. Since it is unknown, whether measurements of Q and V _S can be performed by means of Innocor™ during standard graded exercise tests (GXTs), and whether current GXT stages are sufficiently long for the measurements to take place, we determined Q and V _S at an early and late point in time on submaximal 2 min GXT stages. 16 male cyclists (age 25.4 ± 2.9 years, body mass 71.2 ± 5.0 kg) performed three GXTs and we determined Q and V _S after 46 and 103 s at 69, 77, and 85% peak power. We found that the rebreathings could easily be incorporated into the GXTs and that Q and V _S remained unchanged between the two points in time on the same GXT stage (69% peak power, Q: 18.1 ± 2.1 vs. 18.2 ± 2.3 l min⁻¹, V _S: 126 ± 18 vs. 123 ± 21 ml; 77% peak power, Q: 20.7 ± 2.6 vs. 21.0 ± 2.3 l min⁻¹, V _S: 132 ± 18 vs. 131 ± 18 ml; 85% peak power, Q: 21.6 ± 2.4 vs. 21.8 ± 2.7 l min⁻¹, V _S: 131 ± 17 vs. 131 ± 22 ml). We conclude that Innocor™ may be a useful device for assessing Q and V _S during GXTs, and that the adaptation of Q and V _S to exercise-to-exercise transitions at moderate to high submaximal power outputs is fast enough for 1 and 2 min GXT stage durations.     

The effects of sildenafil and acetazolamide on breathing efficiency and ventilatory control during hypoxic exercise

The reduced arterial oxygen tension at high altitude impairs the ability to work. Acetazolamide improves arterial oxygen saturation (SaO₂) by increasing ventilation but is associated with an increased work and cost of breathing. Depending on the settings, sildenafil can also increases SaO₂ possibly through a reduction in pulmonary hypertension and interstitial edema, which could improve ventilation–perfusion matching. The objective of this study is to determine the effects of acetazolamide and sildenafil on ventilatory control and breathing efficiency (V _E/VCO₂) during submaximal steady-state hypoxic exercise in healthy individuals. Following 18 h of hypoxic exposure in an altitude tent at an oxygen concentration of 12.5% (simulated altitude of 4,300 m), 15 participants performed 10 min of hypoxic exercise on a stationary bicycle at 40% of their sea level peak oxygen uptake (VO₂) while randomly receiving sildenafil 40 mg (SIL), acetazolamide 125 mg (ACZ) or a placebo (PLA). There was no difference in VO₂ during exercise between conditions while SaO₂ was greater with acetazolamide compared to both placebo and sildenafil. Acetazolamide increased ventilation (PLA 49.0 ± 3.2, SIL 47.7 ± 3.1, ACZ 52.1 ± 3.0 l/min) and reduced end-tidal CO₂ (P _ETCO₂) (PLA 32.1 ± 0.8, SIL 32.8 ± 0.9, ACZ 29.2 ± 0.7 mmHg) compared to placebo and sildenafil. Breathing was less efficient with acetazolamide (increased V _E/VCO₂) in comparison to placebo and sildenafil (PLA 41.5 ± 1.0, SIL 40.4 ± 1.3, ACZ 45.4 ± 1.0) while sildenafil did not change V _E/VCO₂ during hypoxic exercise. In conclusion, acetazolamide increased ventilation and reduced breathing efficiency while sildenafil did not affect breathing efficiency despite a trend toward a blunted ventilatory response, possibly due to a reduction in pulmonary hypertension and/or ventilatory drive, during submaximal hypoxic exercise in healthy individuals.     

The effect of a carbohydrate beverage on the physiological responses during prolonged load carriage

Effects of a carbohydrate beverage on the physiological responses to load carriage were examined. Ten fit male participants (age: 28 ± 9 years, body mass: 81.5 ± 10.5 kg, [(V)\dot] \dot{V} O_2max: 55.0 ± 5.5 mL kg⁻¹ min⁻¹) completed two test conditions in random order, walking on a treadmill (6.5 km h⁻¹) for 120 min, carrying a 25-kg backpack. At 0 and 60 min of exercise participants consumed 250 mL of a placebo (flavoured water) (PLA) or 6.4% carbohydrate (CHO) beverage. There were no differences in [(V)\dot] \dot{V} O_2, respiratory exchange ratio (RER), heart rate or EMG activity of m. rectus femoris, m. vastus lateralis, m. semitendinosus and m. biceps femoris between conditions at minute 5 of exercise. The increase in [(V)\dot] \dot{V} O₂ between minutes 5 and 120 was less during CHO than PLA (8 ± 5 vs. 14 ± 6%, P = 0.036). RER decreased during PLA, from 0.96 ± 0.05 at minute 5 to 0.87 ± 0.04 at minute 120 (P < 0.001), but not during CHO (P = 0.056). Heart rate increased between minutes 5 and 120 during PLA (16 ± 10%, P < 0.001) and CHO (12 ± 6%, P < 0.001), with no difference between conditions (P = 0.251). EMG peak RMS did not change between minutes 7 and 107 during PLA or CHO for the leg muscles. However, individual responses in EMG were highly variable (i.e. both increases and decreases in RMS). It was concluded that carbohydrate intake during load carriage reduced the [(V)\dot] \dot{V} O₂ drift, which could be partially attributed to higher carbohydrate oxidation rates. Despite muscle fatigue/damage previously being identified as a cause of [(V)\dot] \dot{V} O₂ drift, it appears that carbohydrate had no effect on neuromuscular responses during load carriage.     

A comparison of normal versus low dietary carbohydrate intake on substrate oxidation during and after moderate intensity exercise in women

We compared the effects of consuming a 2-day low-carbohydrate (CHO) diet (low-CHO; 20% CHO, 40% protein, 40% fat) versus an isocaloric 2-day moderate-CHO diet (mod-CHO; 55% CHO, 15% protein, 30% fat) on substrate oxidation during and after exercise in ten active, young women. Subjects were 24.9 ± 6.2% body fat with a VO_2max of 68.8 ± 13.8 ml/kg FFM/min. For 2 days prior to exercise, subjects consumed either the mod-CHO or the low-CHO diet and then completed treadmill exercise at 55% of VO_2max until 350 kcal of energy was expended. During exercise and for 2 h post-exercise, expired gases were analyzed to determine oxidation rates for CHO (CHO-OX) and fat (FAT-OX). Significant differences (p < 0.05) were found between diets for CHO-OX and FAT-OX (mg/kg FFM/min) during exercise, 1 h post-ex, and 2 h post-ex. During exercise, FAT-OX was higher (low-CHO 8.7 ± 2.2 vs. mod-CHO 6.2 ± 2.2) and CHO-OX was lower (low-CHO 25.1 ± 5.6 vs. mod-CHO 31.1 ± 6.2) following the low-CHO diet. A similar trend was observed during 1 h post-ex for FAT-OX (low-CHO 2.2 ± 0.5 vs. mod-CHO 1.6 ± 0.5) and CHO-OX (low-CHO 2.5 ± 1.2 vs. mod-CHO 4.1 ± 1.9), as well as 2 h post-ex for FAT-OX (low-CHO vs. 1.9 ± 0.5 mod-CHO 1.7 ± 0.4) and CHO-OX (low-CHO 2.5 ± 0.9 vs. mod-CHO 3.1 ± 1.1). Significant positive correlations were observed between VO_2max and CHO-OX during exercise and post-exercise, as well as significant negative correlations between VO_2max and FAT-OX post-exercise in the low-CHO condition. Waist circumference and FAT-OX exhibited a significant negative correlation during exercise in the low-CHO condition. Dietary macronutrient intake influenced substrate oxidation in active young women during and after moderate intensity exercise.     

Experimental design and modelling approach to evaluate efficacy of β-lactam/β-lactamase inhibitor combinations

BackgroundA β-lactamase inhibitor (BLI) confers susceptibility of β-lactamase-expressing multidrug resistant (MDR) organisms to the partnering β-lactam (BL).AimsTo discuss the experimental design and modelling strategies for two-drug combinations, using ceftazidime- and aztreonam-avibactam combinations, as examples.SourcesThe information came from several publications on avibactam in vitro time-kill studies and corresponding pharmacodynamic models.ContentThe experimental design to optimally gather crucial information from constant-concentration time-kill studies is to use an agile matrix of two-drug concentration combinations that cover 0.25- to 4-fold BL minimum inhibitory concentration (MIC) relative to the BLI concentrations to be tested against the particular isolate. This shifting agile design can save substantial costs and resources, without sacrificing crucial information needed for model development. The complex synergistic BL/BLI interaction is quantitatively explored using a semi-mechanistic pharmacokinetic-pharmacodynamic (PK/PD) mathematical model that accounts for antimicrobial activities in the combination, bacteria-mediated BL degradation and inhibition of BL degradation by BLI. A predictive mathematical formulation for the two-drug killing effects preserves the correlation between the model-derived EC₅₀ of BL and the BL MIC. The predictive value of PK/PD model is evaluated against external data that were not used for model development, including but not limited to in vitro hollow fibre and in vivo murine infection models.ImplicationsAs a framework for translational predictions, the goal of this modelling strategy is to significantly decrease the decision-making time by running clinical trial simulations with MIC-substituted EC₅₀ function for isolates of comparable susceptibility through established correlation between BL MIC and EC₅₀ values.