Pharmacometrics to characterize innate immune response and antibacterial treatments

The immune system protects the host against pathogens by distinguishing self from non-self. However, it is most-often disregarded in pharmacokinetic-pharmacodynamic (PKPD) characterization of (new and old) antibiotics. Furthermore, the immune response may become dysregulated and result in life-threatening organ dysfunction, a clinical syndrome known as sepsis. In this work, assessment of immune-response time-courses and anti-bacterial treatments is made by use of non-linear mixed effects models.  Analysis of in vitro and in vivo data characterized neutrophil-mediated phagocytosis of bacteria, and enabled prediction of neutrophil-bacteria dynamics in cancer patients. Further, in vitro bacterial release of lipopolysaccharide (LPS), a bacterial product that stimulates the innate mammalian immune response, was linked to natural bacterial growth and antibiotic-induced killing. In porcine studies, infused LPS and the resultant immune response, characterized by the two biomarkers tumor necrosis factor α and interleukin-6, was described with incorporation of tolerance dynamics. Further, developing organ dysfunction was characterized across cardiovascular, respiratory and blood-related variables, by utilizing physiologic relationships, providing significant insight into time-courses of sepsis. The translational potential of the preclinical models were assessed by scaling them to studies with LPS administration to healthy volunteers, identifying key differences in susceptibility to LPS and showing that humans respond stronger at much lower doses. The PK characteristics of piperacillin (a β-lactam antibiotic) was determined in four patient populations with the aim of optimizing treatment regimens. Whereas renal function determined antibiotic concentration-time course in critically ill patients, body weight was of higher importance in children. Aside from patients with augmented renal clearance or highly-insusceptible pathogens, probability to achieve fT>MIC-related PKPD targets increased with extended or continuous infusion regimens. The models developed in this thesis adds significantly to the quantitative understanding of time-courses in relation to host immune response, bacteria and antibacterial treatments

Pharmacometrics to characterize innate immune response and antibacterial treatments

The immune system protects the host against pathogens by distinguishing self from non-self. However, it is most-often disregarded in pharmacokinetic-pharmacodynamic (PKPD) characterization of (new and old) antibiotics. Furthermore, the immune response may become dysregulated and result in life-threatening organ dysfunction, a clinical syndrome known as sepsis. In this work, assessment of immune-response time-courses and anti-bacterial treatments is made by use of non-linear mixed effects models.  Analysis of in vitro and in vivo data characterized neutrophil-mediated phagocytosis of bacteria, and enabled prediction of neutrophil-bacteria dynamics in cancer patients. Further, in vitro bacterial release of lipopolysaccharide (LPS), a bacterial product that stimulates the innate mammalian immune response, was linked to natural bacterial growth and antibiotic-induced killing. In porcine studies, infused LPS and the resultant immune response, characterized by the two biomarkers tumor necrosis factor α and interleukin-6, was described with incorporation of tolerance dynamics. Further, developing organ dysfunction was characterized across cardiovascular, respiratory and blood-related variables, by utilizing physiologic relationships, providing significant insight into time-courses of sepsis. The translational potential of the preclinical models were assessed by scaling them to studies with LPS administration to healthy volunteers, identifying key differences in susceptibility to LPS and showing that humans respond stronger at much lower doses. The PK characteristics of piperacillin (a β-lactam antibiotic) was determined in four patient populations with the aim of optimizing treatment regimens. Whereas renal function determined antibiotic concentration-time course in critically ill patients, body weight was of higher importance in children. Aside from patients with augmented renal clearance or highly-insusceptible pathogens, probability to achieve fT>MIC-related PKPD targets increased with extended or continuous infusion regimens. The models developed in this thesis adds significantly to the quantitative understanding of time-courses in relation to host immune response, bacteria and antibacterial treatments

Model‐based assessment of neutrophil‐mediated phagocytosis and digestion of bacteria across in vitro and in vivo studies

Neutrophil granulocytes are key components of the host response against pathogens, and severe neutropenia, with neutrophil counts below 0.5 × 106 cells/mL, renders patients increasingly vulnerable to infections. Published in vitro (n = 7) and in vivo (n = 5) studies with time-course information on bacterial and neutrophil counts were digitized to characterize the kinetics of neutrophil-mediated bacterial killing and inform on the immune systems' contribution to the clearance of bacterial infections. A mathematical model for the in vitro dynamics of bacteria and the kinetics of neutrophil-mediated phagocytosis and digestion was developed, which was extended to in vivo studies in immune-competent and immune-compromised mice. Neutrophil-mediated bacterial killing was described by two first-order processes—phagocytosis and digestion—scaled by neutrophil concentration, where 50% of the maximum was achieved at neutrophil counts of 1.19 × 106 cells/mL (phagocytosis) and 6.55 × 106 cells/mL (digestion). The process efficiencies diminished as the phagocytosed bacteria to total neutrophils ratio increased (with 50% reduction at a ratio of 3.41). Neutrophil in vivo dynamics were captured through the characterization of myelosuppressive drug effects and postinoculation neutrophil influx into lungs and by system differences (27% bacterial growth and 9.3% maximum capacity, compared with in vitro estimates). Predictions showed how the therapeutically induced reduction of neutrophil counts enabled bacterial growth, especially when falling below 0.5 × 106 cells/mL, whereas control individuals could deal with all tested bacterial burdens (up to 109 colony forming units/g lung). The model-based characterization of neutrophil-mediated bacterial killing simultaneously predicted data across in vitro and in vivo studies and may be used to inform the capacity of host–response at the individual level.De två första författarna delar förstaförfattarskapet</p

Extension of Pharmacokinetic/Pharmacodynamic Time-Kill Studies To Include Lipopolysaccharide/Endotoxin Release from Escherichia coli Exposed to Cefuroxime.

The release of inflammatory bacterial products, such as lipopolysaccharide (LPS)/endotoxin, may be increased upon the administration of antibiotics. An improved quantitative understanding of endotoxin release and its relation to antibiotic exposure and bacterial growth/killing may be gained by an integrated analysis of these processes. The aim of this work was to establish a mathematical model that relates Escherichia coli growth/killing dynamics at various cefuroxime concentrations to endotoxin release in vitro Fifty-two time-kill experiments informed bacterial and endotoxin time courses and included both static (0×, 0.5×, 1×, 2×, 10×, and 50× MIC) and dynamic (0×, 15×, and 30× MIC) cefuroxime concentrations. A model for the antibiotic-bacterium interaction was established, and antibiotic-induced bacterial killing followed a sigmoidal Emax relation to the cefuroxime concentration (MIC-specific 50% effective concentration [EC50], maximum antibiotic-induced killing rate [E max] = 3.26 h-1 and γ = 3.37). Endotoxin release was assessed in relation to the bacterial processes of growth, antibiotic-induced bacterial killing, and natural bacterial death and found to be quantitatively related to bacterial growth (0.000292 endotoxin units [EU]/CFU) and antibiotic-induced bacterial killing (0.00636 EU/CFU). Increased release following the administration of a second cefuroxime dose was described by the formation and subsequent antibiotic-induced killing of filaments (0.295 EU/CFU). Release due to growth was instantaneous, while release due to antibiotic-induced killing was delayed (mean transit time of 7.63 h). To conclude, the in vitro release of endotoxin is related to bacterial growth and antibiotic-induced killing, with higher rates of release upon the killing of formed filaments. Endotoxin release over 24 h is lowest when antibiotic exposure rapidly eradicates bacteria, while increased release is predicted to occur when growth and antibiotic-induced killing occur simultaneously

Population pharmacokinetics of piperacillin in febrile children receiving cancer chemotherapy : the impact of body weight and target on an optimal dosing regimen

Background The β-lactam antibiotic piperacillin (in combination with tazobactam) is commonly chosen for empirical treatment of suspected bacterial infections. However, pharmacokinetic variability among patient populations and across ages leads to uncertainty when selecting a dosing regimen to achieve an appropriate pharmacodynamic target. Objectives To guide dosing by establishing a population pharmacokinetic model for unbound piperacillin in febrile children receiving cancer chemotherapy, and to assess pharmacokinetic/pharmacodynamic target attainment (100% fT&gt;1xMIC and 50% fT&gt;4xMIC) and resultant exposure, across body weights. Methods Forty-three children admitted for 89 febrile episodes contributed 482 samples to the pharmacokinetic analysis. The typical doses required for target attainment were compared for various dosing regimens, in particular prolonged infusions, across MICs and body weights. Results A two-compartment model with inter-fever-episode variability in CL, and body weight included through allometry, described the data. A high CL of 15.4L/h (70kg) combined with high glomerular filtration rate (GFR) values indicated rapid elimination and hyperfiltration. The target of 50% fT&gt;4xMIC was achieved for an MIC of 4.0mg/L in a typical patient with extended infusions of 2-3 (q6h) or 3-4 (q8h)h, at or below the standard adult dose (75 and 100mg/kg/dose for q6h and q8h, respectively). Higher doses or continuous infusion were needed to achieve 100% fT&gt;1xMIC due to the rapid piperacillin elimination. Conclusions The licensed dose for children with febrile neutropenia (80mg/kg q6h as a 30min infusion) performs poorly for attainment of fT&gt;MIC pharmacokinetic/pharmacodynamic targets. Given the population pharmacokinetic profile, feasible dosing regimens with reasonable exposure are continuous infusion (100% fT&gt;1xMIC) or prolonged infusions (50% fT&gt;4xMIC)

Continuous infusion of piperacillin‐tazobactam significantly improves target attainment in children with cancer and fever

Background Children with febrile neutropenia commonly exhibit alterations of pharmacokinetic (PK) parameters, leading to decreased β-lactam concentrations. Aims This study evaluated piperacillin PK and probability of target attainment (PTA) with continuous infusion of piperacillin-tazobactam, in order to optimize the dosing regimen. Methods This prospective PK study included children with cancer, aged 1–17 years, who were treated with piperacillin-tazobactam for suspected or verified infection. A piperacillin-tazobactam loading dose (100 mg/kg) was administered followed by continuous infusion (300 mg/kg/day). The unbound fraction of piperacillin was quantified by high-performance liquid chromatography and PK were described using population PK modeling. PK data was used to update and extend a previous PK model built on data following intermittent administration. Monte Carlo simulations were performed to assess PTA for targets of 100% time above the minimum inhibitory concentration (100% fT &gt; MIC) and 50% fT &gt; 4xMIC. Results We included 68 fever episodes among 38 children with a median (IQR) age of 6.5 years and body weight of 27.4 kg (15.1–54.0). A three-compartment model adequately described the concentration-time data. Median (95% confidence interval) estimates for clearance and piperacillin concentration at steady state were 14.2 L/h/70 kg (13.0; 15.3) and 47.6 mg/L (17.2; 129.5), respectively. Body weight or lean body weight was significantly associated with the PK parameters, and body weight was integrated in the final PK model. Based on piperacillin exposure, continuous infusion was the only dosing regimen to achieve optimal PTA for the P. aeruginosa breakpoint (16 mg/L) with the target of 100% fT &gt; MIC, and a daily dose of 300 mg/kg reached optimal PTA. The strict target of 50% fT &gt; 4xMIC (64 mg/L) was not feasibly attained by any dosing regimen at recommended doses. Conclusion Unlike conventional piperacillin intermittent administration and extended infusion regimens, continuous infusion allows the target of 100% fT &gt; MIC to be reached for children with febrile neutropenia

A non-linear mixed effect model for innate immune response : In vivo kinetics of endotoxin and its induction of the cytokines tumor necrosis factor alpha and interleukin-6

Endotoxin, a component of the outer membrane of Gram-negative bacteria, has been extensively studied as a stimulator of the innate immune response. However, the temporal aspects and exposure-response relationship of endotoxin and resulting cytokine induction and tolerance development is less well defined. The aim of this work was to establish an in silico model that simultaneously captures and connects the in vivo time-courses of endotoxin, tumor necrosis factor alpha (TNF-alpha), interleukin-6 (IL-6), and associated tolerance development. Data from six studies of porcine endotoxemia in anesthetized piglets (n = 116) were combined and used in the analysis, with purified endotoxin (Escherichia coli O111: B4) being infused intravenously for 1-30 h in rates of 0.063-16.0 mu g/kg/h across studies. All data were modelled simultaneously by means of importance sampling in the non-linear mixed effects modelling software NONMEM. The infused endotoxin followed one-compartment disposition and non-linear elimination, and stimulated the production of TNF-alpha to describe the rapid increase in plasma concentration. Tolerance development, observed as declining TNF-alpha concentration with continued infusion of endotoxin, was also driven by endotoxin as a concentration-dependent increase in the potency parameter related to TNF-alpha production (EC50). Production of IL-6 was stimulated by both endotoxin and TNF-a, and four consecutive transit compartments described delayed increase in plasma IL-6. A model which simultaneously account for the time-courses of endotoxin and two immune response markers, the cytokines TNF-alpha and IL-6, as well as the development of endotoxin tolerance, was successfully established. This model-based approach is unique in its description of the time-courses and their interrelation and may be applied within research on immune response to bacterial endotoxin, or in pre-clinical pharmaceutical research when dealing with study design or translational aspects

Population pharmacokinetics of piperacillin in plasma and subcutaneous tissue in patients on continuous renal replacement therapy

OBJECTIVES: Piperacillin is a β-lactam antimicrobial frequently used in critically ill patients with acute kidney injury treated with continuous renal replacement therapy (CRRT). However, data regarding piperacillin tissue concentrations in this patient population are limited. A prospective observational study was conducted of free piperacillin concentrations during a single 8-h dosing interval in plasma (8 samples) and subcutaneous tissue (SCT) (13 samples), in 10 patients treated with CRRT following piperacillin 4 g given every 8 h as intermittent administration over 3 min. METHODS: A population pharmacokinetic model was developed using NONMEM 7.4.3, to simulate alternative administration modes and dosing regimens. SCT concentrations were obtained using microdialysis. Piperacillin concentrations were compared to the clinical breakpoint minimum inhibitory concentration (MIC) for Pseudomonas aeruginosa (16 mg/l), with evaluation of the following pharmacokinetic/pharmacodynamics targets: 50% fT &gt; 1 × MIC, 100% fT &gt; 1 × MIC, and 100% fT &gt; 4 × MIC. RESULTS: SCT concentrations were generally lower than plasma concentrations. For the target of 50% free time (fT) &gt; 1 × MIC and 100% fT &gt; 1 × MIC, piperacillin 4 g every 8 h resulted in probability of target attainment (PTA) &gt;90% in both plasma and SCT. PTA &gt; 90% for the target of 100% fT &gt; 4 × MIC was only achieved for continuous infusion. CONCLUSIONS: Piperacillin 4 g every 8 h is likely to provide sufficient exposure in both plasma and SCT to treat P.aeruginosa infections in critically ill patients on CRRT, given that targets of 50% fT &gt; 1 × MIC or 100% fT &gt; 1 × MIC are adequate. However, if a more aggressive target of 100% fT &gt; 4 × MIC is adopted, continuous infusion is needed