1321. Population Pharmacokinetic (PK) and Pharmacokinetic/Pharmacodynamic (PK/PD) Target Attainment Analyses for Dalbavancin in Pediatric Patients

Abstract Background Dalbavancin is a lipoglycopeptide approved for treating adults with acute bacterial skin and skin structure infections (ABSSSI). It has a terminal half-life of >14 days, which allows for administration as a single-dose regimen. Pediatric studies for dalbavancin include three phase 1 studies and a phase 3 study in patients from birth to 17 years with ABSSSI or neonatal sepsis. Methods A population PK model was developed using 1124 concentrations from 211 pediatric patients. Allometric scaling of clearance, and volume parameters was included with exponents fixed at 0.75 and 1, respectively. Based on exploratory analysis and prior knowledge, serum albumin was included as a covariate on all PK parameters, and creatinine clearance or estimated glomerular filtration rate (eGFR) was included as a covariate on clearance. eGFR for patients < 2 years accounted for renal maturation. Additional covariates were assessed by stepwise covariate modeling (SCM). The final model was qualified by visual predictive checks (VPCs) and bootstrapping and was used to simulate 1000 PK profiles for various pediatric age groups, ranging from preterm neonates to adolescents. PK/PD target attainment (PTA) was calculated for targets associated with stasis, 1-log kill, and 2-log kill of Staphylococcus aureus in the murine thigh infection model. Results Dalbavancin PK was well-characterized by a 3-compartment model. SCM did not find any significant covariates besides albumin, weight, and renal function. VPCs demonstrated that the final model has good predictive performance across the full age range. Simulations showed that single-dose regimens of 22.5 mg/kg for patients < 6 years and 18 mg/kg for patients 6 to < 18 years resulted in PTA ≥94% for MICs up to 2 mg/L for the stasis target and up to 0.5 mg/L for the 2-log kill target. PTA for pediatric patients was similar to adults, and exposures (AUCs) were contained within the range for adults administered 1500 mg. Conclusion Dalbavancin PK in pediatric patients was well-characterized by a 3-compartment model with allometric scaling of clearance and volume and with albumin and renal function included as covariates. Simulations with the final model demonstrate adequate PTA across the entire age range for the regimens used in the phase 3 pediatric study. Disclosures Timothy J. Carrothers, ScD, AbbVie (Employee) H. Maxime Lagraauw, PhD, qPharmetra (Employee) Lars Lindbom, PhD, qPharmetra (Employee) Todd Riccobene, PhD, AbbVie (Employee)

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1573. Population Pharmacokinetic Analyses for Cefepime in Adult and Pediatric Patients

Open Forum Infectious Diseases ◽

10.1093/ofid/ofz360.1437 ◽

2019 ◽

Vol 6 (Supplement_2) ◽

pp. S574-S575

Author(s):

Jiajun Liu ◽

Michael Neely ◽

Jeffrey Lipman ◽

Fekade B Sime ◽

Jason Roberts ◽

...

Keyword(s):

Rate Constant ◽

Pediatric Patients ◽

Validation Cohort ◽

External Validation ◽

Compartment Model ◽

Volume Of Distribution ◽

Information Criteria ◽

Population Pharmacokinetic ◽

Final Model ◽

Two Compartment Model

Abstract Background Cefepime (CEF) is commonly used for adult and pediatric infections. Several studies have examined CEF’s pharmacokinetics (PK) in various populations; however, a unifying PK model for adult and pediatric subjects does not yet exist. We developed a combined population model for adult and pediatric patients and validated the model. Methods The initial model includes adult and pediatric patients with a rich cefepime sampling design. All adults received 2 g CEF while pediatric subjects received a mean of 49 (SD 5) mg/kg. One- and two-compartment models were considered as base models and were fit using a non-parametric adaptive grid algorithm within the Pmetrics package 1.5.2 (Los Angeles, CA) for R 3.5.1. Compartmental model selection was based on Akaike information criteria (AIC). Covariate relationships with PK parameters were visually inspected and mathematically assessed. Predictive performance was evaluated using bias and imprecision of the population and individual prediction models. External validation was conducted using a separate adult cohort. Results A total of 45 subjects (n = 9 adults; n = 36 pediatrics) were included in the initial PK model build and 12 subjects in the external validation cohort. Overall, the data were best described using a two-compartment model with volume of distribution (V) normalized to total body weight (TBW/70 kg) and an allometric scaled elimination rate constant (Ke) for pediatric subjects (AIC = 4,138.36). Final model observed vs. predicted plots demonstrated good fit (population R2 = 0.87, individual R2 = 0.97, Figure 1a and b). For the final model, the population median parameter values (95% credibility interval) were V0 (total volume of distribution), 11.7 L (10.2–14.6); Ke for adult, 0.66 hour−1 (0.38–0.78), Ke for pediatrics, 0.82 hour−1 (0.64–0.85), KCP (rate constant from central to peripheral compartment), 1.4 hour−1 (1.3–1.8), KPC (rate constant from peripheral to central compartment), 1.6 hour−1 (1.2–1.8). The validation cohort has 12 subjects, and the final model fit the data well (individual R2 = 0.75). Conclusion In this diverse group of adult and pediatrics, a two-compartment model described CEF PK well and was externally validated with a unique cohort. This model can serve as a population prior for real-time PK software algorithms. Disclosures All authors: No reported disclosures.

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1567. Pharmacokinetic/Pharmacodynamic Target Attainment in Adult and Pediatric Patients following Administration of Ceftaroline Fosamil as a 5-Minute Infusion

Open Forum Infectious Diseases ◽

10.1093/ofid/ofz360.1431 ◽

2019 ◽

Vol 6 (Supplement_2) ◽

pp. S572-S573

Author(s):

Todd Riccobene ◽

T J Carrothers, ScD ◽

William Knebel ◽

Susan Raber ◽

Phylinda L S Chan

Keyword(s):

Renal Function ◽

Normal Renal Function ◽

Dose Regimen ◽

Pediatric Patients ◽

Systemic Exposure ◽

The United States ◽

Simulated Patients ◽

Population Pharmacokinetic ◽

Target Attainment ◽

Ceftaroline Fosamil

Abstract Background Ceftaroline fosamil is approved in the United States for treating patients ≥2 months old with acute bacterial skin and skin structure infections and community-acquired bacterial pneumonia, and for similar indications in Europe. The active metabolite, ceftaroline, has in vitro activity against common Gram-positive pathogens, including methicillin-resistant Staphylococcus aureus and Streptococcus pneumoniae. Population pharmacokinetic (popPK) modeling and simulation were used to assess systemic exposure and PK/pharmacodynamic (PK/PD) target attainment for S. aureus and S pneumoniae for 5- and 60-minute infusions. Methods A simultaneous popPK model, including 2 compartments each, for ceftaroline fosamil and ceftaroline was previously developed using an extensive database of adult and pediatric data. An effect of renal function maturation as a function of postmenstrual age was included on ceftaroline clearance for children <2 years. This model was used to conduct simulations for-approved ceftaroline doses administered as 5- and 60-min infusions to adult and pediatric patients with normal renal function and mild renal impairment. For adults, 100 simulations of 300 patients each were performed for each dose regimen, and covariates were generated from a multivariate normal distribution using covariate correlations from observed data. For pediatric patients, 100 simulations were performed for each dose regimen with 600 patients in each 1-month age group. Weights for pediatric age groups were based on CDC growth charts. Results The median proportion of simulated patients with normal renal function achieving %fT>MIC targets of 35% and 44% (associated with 1-log kill of S. aureus and S pneumoniae, respectively), are shown for 5- and 60-min infusions (figure). PK/PD target attainment was similar for both infusion times and was >99% at an MIC of 1 mg/L for S. aureus and an MIC of 0.5 mg/L for S pneumoniae. Ceftaroline AUC was similar for both infusion times, and Cmax was approximately 30%–40% higher for the 5-min infusion. Conclusion Ceftaroline fosamil gave as a 5-min infusion to adult and pediatric patients ≥2 months of age achieved similar PK/PD target attainment as a 60-min infusion for S. aureus and S pneumoniae for MICs up to 1 mg/L and 0.5 mg/L, respectively. Disclosures All authors: No reported disclosures.

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Model-Informed Optimization of a Pediatric Clinical Pharmacokinetic Trial of a New Spironolactone Liquid Formulation

Pharmaceutics ◽

10.3390/pharmaceutics13060849 ◽

2021 ◽

Vol 13 (6) ◽

pp. 849

Author(s):

Manasa Tatipalli ◽

Vijay Kumar Siripuram ◽

Tao Long ◽

Diana Shuster ◽

Galina Bernstein ◽

...

Keyword(s):

Pharmacokinetic Model ◽

Allometric Scaling ◽

Pediatric Patients ◽

Reference Product ◽

Population Pharmacokinetic ◽

Liquid Formulation ◽

Sampling Schemes ◽

Quantitative Pharmacology ◽

Using Data ◽

Drug Pharmacokinetics

Quantitative pharmacology brings important advantages in the design and conduct of pediatric clinical trials. Herein, we demonstrate the application of a model-based approach to select doses and pharmacokinetic sampling scenarios for the clinical evaluation of a novel oral suspension of spironolactone in pediatric patients with edema. A population pharmacokinetic model was developed and qualified for spironolactone and its metabolite, canrenone, using data from adults and bridged to pediatrics (2 to <17 years old) using allometric scaling. The model was then used via simulation to explore different dosing and sampling scenarios. Doses of 0.5 and 1.5 mg/kg led to target exposures (i.e., similar to 25 and 100 mg of the reference product in adults) in all the reference pediatric ages (i.e., 2, 6, 12 and 17 years). Additionally, two different sampling scenarios were delineated to accommodate patients into sparse sampling schemes informative to characterize drug pharmacokinetics while minimizing phlebotomy and burden to participating children.

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Population Pharmacokinetic Modeling and Pharmacodynamic Target Attainment Simulation of Piperacillin/Tazobactam for Dosing Optimization in Late Elderly Patients with Pneumonia

Antibiotics ◽

10.3390/antibiotics9030113 ◽

2020 ◽

Vol 9 (3) ◽

pp. 113 ◽

Cited By ~ 1

Author(s):

Noriyuki Ishihara ◽

Nobuhiro Nishimura ◽

Kazuro Ikawa ◽

Fumi Karino ◽

Kiyotaka Miura ◽

...

Keyword(s):

Plasma Concentration ◽

Elderly Patients ◽

Distribution Volume ◽

Population Pharmacokinetic ◽

Parameter Estimates ◽

Target Attainment ◽

Old Patients ◽

Final Model ◽

Concentration Time ◽

Population Pk

The aim of this study was to develop a population pharmacokinetic model for piperacillin (PIPC)/tazobactam (TAZ) in late elderly patients with pneumonia and to optimize the administration planning by applying pharmacokinetic/pharmacodynamic (PK/PD) criteria. PIPC/TAZ (total dose of 2.25 or 4.5 g) was infused intravenously three times daily to Japanese patients over 75 years old. The plasma concentrations of PIPC and TAZ were determined using high-performance liquid chromatography and modeled using the NONMEM program. PK/PD analysis with a random simulation was conducted using the final population PK model to estimate the probability of target attainment (PTA) profiles for various PIPC/TAZ-regimen–minimum-inhibitory-concentration (MIC) combinations. The PTAs for PIPC and TAZ were determined as the fraction that achieved at least 50% free time > MIC and area under the free-plasma-concentration–time curve over 24 h ≥ 96 μg h/mL, respectively. A total of 18 cases, the mean age of which was 86.5 ± 6.0 (75–101) years, were investigated. The plasma-concentration–time profiles of PIPC and TAZ were characterized by a two-compartment model. The parameter estimates for the final model, namely the total clearance, central distribution volume, peripheral distribution volume, and intercompartmental clearance, were 4.58 + 0.061 × (CLcr − 37.4) L/h, 5.39 L, 6.96 L, and 20.7 L/h for PIPC, and 5.00 + 0.059 × (CLcr − 37.4) L/h, 6.29 L, 7.73 L, and 24.0 L/h for TAZ, respectively, where CLcr is the creatinine clearance. PK/PD analysis using the final model showed that in drug-resistant strains with a MIC > 8 μg/mL, 4.5 g of PIPC/TAZ every 6 h was required, even for the patients with a CLcr of 50–60 mL/min. The population PK model developed in this study, together with MIC value, can be useful for optimizing the PIPC/TAZ dosage in the over-75-year-old patients, when they are administered PIPC/TAZ. Therefore, the findings of present study may contribute to improving the efficacy and safety of the administration of PIPC/TAZ therapy in late elderly patients with pneumonia.

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Population Pharmacokinetics and Dosing Optimization of Linezolid in Pediatric Patients

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.02387-18 ◽

2019 ◽

Vol 63 (4) ◽

Cited By ~ 2

Author(s):

Si-Chan Li ◽

Qi Ye ◽

Hua Xu ◽

Long Zhang ◽

Yang Wang

Keyword(s):

Body Weight ◽

Population Pharmacokinetics ◽

Population Pharmacokinetic Model ◽

Pharmacokinetic Model ◽

Pediatric Patients ◽

Population Pharmacokinetic ◽

Pharmacokinetic Data ◽

Nonparametric Bootstrap ◽

Bootstrap Analysis ◽

Final Model

ABSTRACT Linezolid is a synthetic antibiotic very effective in the treatment of infections caused by Gram-positive pathogens. Although the clinical application of linezolid in children has increased progressively, data on linezolid pharmacokinetics in pediatric patients are very limited. The aim of this study was to develop a population pharmacokinetic model for linezolid in children and optimize the dosing strategy in order to improve therapeutic efficacy. We performed a prospective pharmacokinetic study of pediatric patients aged 0 to 12 years. The population pharmacokinetic model was developed using the NONMEM program. Goodness-of-fit plots, nonparametric bootstrap analysis, normalized prediction distribution errors, and a visual predictive check were employed to evaluate the final model. The dosing regimen was optimized based on the final model. The pharmacokinetic data from 112 pediatric patients ages 0.03 to 11.9 years were analyzed. The pharmacokinetics could best be described by a one-compartment model with first-order elimination along with body weight and the estimated glomerular filtration rate as significant covariates. Simulations demonstrated that the currently approved dosage of 10 mg/kg of body weight every 8 h (q8h) would lead to a high risk of underdosing for children in the presence of bacteria with MICs of ≥2 mg/liter. To reach the pharmacokinetic target, an elevated dosage of 15 or 20 mg/kg q8h may be required for them. The population pharmacokinetics of linezolid were characterized in pediatric patients, and simulations provide an evidence-based approach for linezolid dosage individualization.

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Ceftolozane/tazobactam probability of target attainment and outcomes in participants with augmented renal clearance from the randomized phase 3 ASPECT-NP trial

Critical Care ◽

10.1186/s13054-021-03773-5 ◽

2021 ◽

Vol 25 (1) ◽

Author(s):

Andrew F. Shorr ◽

Christopher J. Bruno ◽

Zufei Zhang ◽

Erin Jensen ◽

Wei Gao ◽

...

Keyword(s):

Renal Function ◽

Normal Renal Function ◽

Clinical Cure ◽

Bacterial Pneumonia ◽

Target Attainment ◽

Augmented Renal Clearance ◽

Phase 3 ◽

Epithelial Lining Fluid ◽

All Cause Mortality ◽

Cure Rates

Abstract Background The randomized, double-blind, phase 3 ASPECT-NP trial evaluated the efficacy of 3 g of ceftolozane/tazobactam (C/T) versus 1 g of meropenem infused every 8 h for 8 to 14 days for treatment of adults with hospital-acquired bacterial pneumonia (HABP) or ventilator-associated bacterial pneumonia (VABP). We assessed the probability of target attainment and compared efficacy outcomes from ASPECT-NP in participants with augmented renal clearance (ARC) versus those with normal renal function. Methods Baseline renal function was categorized as normal renal function (creatinine clearance 80–130 mL/min) or ARC (creatinine clearance > 130 mL/min). Population pharmacokinetic models informed Monte Carlo simulations to assess probability of target attainment in plasma and pulmonary epithelial lining fluid. Outcomes included 28-day all-cause mortality and clinical cure and per-participant microbiologic cure rates at the test-of-cure visit. Results A > 99% and > 80% probability of target attainment was demonstrated for ceftolozane and tazobactam, respectively, in simulated plasma and epithelial lining fluid. Within treatment arms, 28-day all-cause mortality rates in participants with normal renal function (C/T, n = 131; meropenem, n = 123) and ARC (C/T, n = 96; meropenem, n = 113) were comparable (data comparisons presented as rate; treatment difference [95% CI]) (C/T: normal renal function, 17.6%; ARC, 17.7%; 0.2 [− 9.6 to 10.6]; meropenem: normal renal function, 20.3%; ARC, 17.7%; − 2.6 [− 12.6 to 7.5]). Clinical cure rates at test-of-cure were also comparable across renal function groups within treatment arms (C/T: normal renal function, 57.3%; ARC, 59.4%; − 2.1 [− 14.8 to 10.8]; meropenem: normal renal function, 59.3%; ARC, 57.5%; 1.8 [− 10.6 to 14.2]). Per-participant microbiologic cure rates at test-of-cure were consistent across renal function groups within treatment arms (C/T: normal renal function, 72.2% [n/N = 70/97]; ARC, 71.4% [n/N = 55/77]; 0.7 [− 12.4 to 14.2]; meropenem: normal renal function, 75.0% [n/N = 66/88]; ARC, 70.0% [n/N = 49/70]; 5.0 [− 8.7 to 19.0]). Conclusions C/T and meropenem resulted in 28-day all-cause mortality, clinical cure, and microbiologic cure rates that were comparable between participants with ARC or normal renal function. In conjunction with high probability of target attainment, these results confirm that C/T (3 g) every 8 h is appropriate in patients with HABP/VABP and ARC. Trial registration ClinicalTrials.gov identifier: NCT02070757, registered February 25, 2014; EudraCT: 2012-002862-11.

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Population Pharmacokinetics and Dosing Simulation of Vancomycin Administered by Continuous Injection in Critically Ill Patient

Antibiotics ◽

10.3390/antibiotics10101228 ◽

2021 ◽

Vol 10 (10) ◽

pp. 1228

Author(s):

Romain Garreau ◽

Benoît Falquet ◽

Lisa Mioux ◽

Laurent Bourguignon ◽

Tristan Ferry ◽

...

Keyword(s):

Critically Ill ◽

External Validation ◽

Ideal Body Weight ◽

Intermittent Infusion ◽

Compartment Model ◽

Critically Ill Patient ◽

Population Pharmacokinetic ◽

Measured Concentration ◽

Icu Patients ◽

Final Model

Background: Vancomycin is widely used for empirical antimicrobial therapy in critically ill patients with sepsis. Continuous infusion (CI) may provide more stable exposure than intermittent infusion, but optimal dosing remains challenging. The aims of this study were to perform population pharmacokinetic (PK) analysis of vancomycin administered by CI in intensive care unit (ICU) patients to identify optimal dosages. Methods: Patients who received vancomycin by CI with at least one measured concentration in our center over 16 months were included, including those under continuous renal replacement therapy (CRRT). Population PK was conducted and external validation of the final model was performed in a dataset from another center. Simulations were conducted with the final model to identify the optimal loading and maintenance doses for various stages of estimated creatinine clearance (CRCL) and in patients on CRRT. Target exposure was defined as daily AUC of 400–600 mg·h/L on the second day of therapy (AUC24–48 h). Results: A two-compartment model best described the data. Central volume of distribution was allometrically scaled to ideal body weight (IBW), whereas vancomycin clearance was influenced by CRRT and CRCL. Simulations performed with the final model suggested a loading dose of 27.5 mg/kg of IBW. The maintenance dose ranged from 17.5 to 30 mg/kg of IBW, depending on renal function. Overall, simulation showed that 55.8% (95% CI; 47–64%) of patients would achieve the target AUC with suggested dosages. Discussion: A PK model has been validated for vancomycin administered by CI in ICU patients, including patients under CRRT. Our model-informed precision dosing approach may help for early optimization of vancomycin exposure in such patients.

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Assessment of the nlmixr R-package for population pharmacokinetic modeling: A metformin case study

10.22541/au.163630727.72118368/v1 ◽

2021 ◽

Author(s):

Wen Yao Mak ◽

Qing Xi Ooi ◽

Cintia Cruz ◽

Irene Looi ◽

Kah Hay Yuen ◽

...

Keyword(s):

Compartment Model ◽

Stochastic Simulations ◽

Population Pharmacokinetic ◽

Parameter Estimates ◽

Mixed Effect ◽

Flip Flop ◽

Final Model ◽

Elimination Phase ◽

Transit Compartment ◽

Terminal Elimination Phase

Aim: nlmixr offers first-order conditional estimation with or without interaction (FOCE or FOCEi) and stochastic approximation estimation-maximisation (SAEM) to fit nonlinear mixed-effect models (NLMEM). We modelled metformin’s population pharmacokinetics with flip-flop characteristics within nlmixr framework and investigated SAEM and FOCEi’s performance with respect to bias, precision, and robustness. Method: Compartmental pharmacokinetic models were fitted. The final model was determined based on the lowest objective function value and visual inspection of goodness-of-fit plots. To examine flip-flop pharmacokinetics, k_a values of a typical concentration-time profile based on the final model were perturbed and changes in the steepness of the terminal elimination phase were evaluated. The bias and precision of parameter estimates were compared between SAEM and FOCEi using stochastic simulations and estimations. For robustness, parameters were re-estimated as the initial estimates were perturbed 100-times and resultant changes evaluated. Results: A one-compartment model with transit compartment for absorption best described the data. At low n, Stirling’s approximation of n! over-approximated plasma concentration unlike the log-gamma function. Flip-flop pharmacokinetics were evident as the steepness of the terminal elimination phase changed with k_a. Mean rRMSE for fixed-effect parameters was 0.932. When initial estimates were perturbed, FOCEi estimates of k_a and food effect on k_a appeared bimodal and were upward biased. Discussion: nlmixr is reliable for NLMEM even if flip-flop is present but caution should be exercised when using Stirling’s approximation for n! in the transit compartment model. SAEM was marginally superior to FOCEi in bias and precision, but SAEM was superior against initial estimate perturbations.

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Population Pharmacokinetic Modelling and Simulation to Determine the Optimal Dose of Nanoparticulated Sorafenib to the Reference Sorafenib

Pharmaceutics ◽

10.3390/pharmaceutics13050629 ◽

2021 ◽

Vol 13 (5) ◽

pp. 629

Author(s):

Ki Young Huh ◽

Sejung Hwang ◽

Sang Yeob Park ◽

Hye Jung Lim ◽

Miryung Jin ◽

...

Keyword(s):

Compartmental Analysis ◽

Optimal Dose ◽

Compartment Model ◽

Population Pharmacokinetic ◽

Open Label ◽

Post Dose ◽

Multikinase Inhibitor ◽

Final Model ◽

Fasted State ◽

Second Period

Sorafenib, an oral multikinase inhibitor, exhibits a highly variable absorption profile due to enterohepatic reabsorption and poor solubility. SYO-1644 improved the solubility of sorafenib by nanoparticulation technology leading to enhanced bioavailability. To evaluate the pharmacokinetically equivalent dose of SYO-1644 to the reference Nexavar® 200 mg, a randomized, open-label, replicated two-period study was conducted in healthy volunteers. A total of 32 subjects orally received a single dose of the following assigned treatment under a fasted state in the first period and repeated once more in the second period with a two-week washout: SYO-1644 100, 150 and 200 mg and Nexavar® 200 mg. Pharmacokinetic (PK) samples were collected up to 168 h post-dose. The PK profile was evaluated by both non-compartmental analysis and population PK method. With the final model, 2 × 2 crossover trial scenarios with Nexavar® 200 mg and each dose of SYO-1644 ranging from 100 to 150 mg were repeated 500 times by Monte Carlo simulation, and the proportion of bioequivalence achievement was assessed. Transit absorption compartments, followed by a one-compartment model with first-order elimination and enterohepatic reabsorption components were selected as the final model. The simulation results demonstrated that the SYO-1644 dose between 120 and 125 mg could yielded the highest proportion of bioequivalence.

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Cardiopulmonary Bypass Has Minimal Effects on the Pharmacokinetics of Fentanyl in Adults

Anesthesiology ◽

10.1097/00000542-200310000-00016 ◽

2003 ◽

Vol 99 (4) ◽

pp. 847-854 ◽

Cited By ~ 9

Author(s):

Robert J. Hudson ◽

Ian R. Thomson ◽

Rajive Jassal ◽

David J. Peterson ◽

Aaron D. Brown ◽

...

Keyword(s):

Cardiopulmonary Bypass ◽

Prediction Error ◽

Predictive Accuracy ◽

Predictive Ability ◽

Compartment Model ◽

Pharmacokinetic Parameters ◽

Population Pharmacokinetic ◽

Model Parameters ◽

Final Model ◽

Three Compartment Model

Background Although fentanyl has been widely used in cardiac anesthesia, no complete pharmacokinetic model that has assessed the effect of cardiopulmonary bypass (CPB) and that has adequate predictive accuracy has been defined. The aims of this investigation were to determine whether CPB had a clinically significant impact on fentanyl pharmacokinetics and to determine the simplest model that accurately predicts fentanyl concentrations during cardiac surgery using CPB. Methods Population pharmacokinetic modeling was applied to concentration-versus-time data from 61 patients undergoing coronary artery bypass grafting using CPB. Predictive ability of models was assessed by calculating bias (prediction error), accuracy (absolute prediction error), and measured:predicted concentration ratios versus time. The predictive ability of a simple three-compartment model with no covariates was initially compared to models with premedication (lorazepam vs. clonidine), sex, or weight as covariates. This simple model was then compared to 18 CPB-adjusted models that allowed for step changes in pharmacokinetic parameters at the start and/or end of CPB. The predictive ability of the final model was assessed prospectively in a second group of 29 patients. Results None of the covariate (premedication, sex, weight) models nor any of the CPB-adjusted models significantly improved prediction error or absolute prediction error, compared to the simple three-compartment model. Thus, the simple three-compartment model was selected as the final model. Prospective assessment of this model yielded a median prediction error of +3.8%, with a median absolute prediction error of 15.8%. The model parameters were as follows: V1, 14.4 l; V2, 36.4 l; V3, 169 l; Cl1, 0.82 l. min-1; Cl2, 2.31 l x min-1; Cl3, 1.35 l x min-1. Conclusions Compared to other factors that cause pharmacokinetic variability, the effect of CPB on fentanyl kinetics is clinically insignificant. A simple three-compartment model accurately predicts fentanyl concentrations throughout surgery using CPB.

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