One-compartment Pharmacokinetic Model Research Articles

Population modeling analyses of crizotinib in pediatric patients with ALK-positive advanced cancers.

Alterations in the ALK (anaplastic lymphoma kinase) gene play a critical role in pathogenesis of anaplastic large cell lymphoma (ALCL). Crizotinib is a small molecule competitive inhibitor of ALK, ROS1, and MET kinases and was approved for pediatric patients with ALK-positive relapsed or refractory, systemic ALCL, and ALK-positive unresectable, recurrent, or refractory inflammatory myofibroblastic tumors (IMT). Crizotinib data from pediatric patients with relapsed or refractory solid tumors, IMT, or ALCL were included in the analyses. All patients received crizotinib orally at doses ranging from 100 to 365mg/m2 twice daily (BID). PopPK analyses were conducted to characterize crizotinib disposition in pediatric patients. Exposure-response (ER) safety and antitumor analyses were conducted to characterize relationships between crizotinib dose or exposure with safety and antitumor activity endpoints of interest. The population pharmacokinetic (popPK), ER safety, and ER antitumor analysis included 98, 110, and 36 pediatric patients, respectively. A one-compartment pharmacokinetic model with allometric scaling, first-order elimination, and first-order absorption with lag time adequately described the data. Natural log-transformed model-predicted crizotinib AUCss (steady-state area under the concentration-time curve) demonstrated a significant, positive relationship with Grade ≥3 NEUTROPENIA and Any Grade VISION DISORDER. Crizotinib dose demonstrated a positive relationship with objective response rate. No significant differences in PK were identified across a wide range of ages or across tumor types, suggesting body surface area (BSA)-based dosing adequately adjusted for differences in patient size to achieve similar systemic crizotinib exposures across young children and adolescent pediatric patients. None of the myelosuppressive events except Grade ≥3 NEUTROPENIA had significant relationships identified with crizotinib dose or exposure, suggesting crizotinib is a tolerable treatment with less hematological toxicity than traditional chemotherapy regimens for pediatric patients with ALK-mutated cancers. Results from the presented analyses support the pediatric dosing recommendations in the product label.

Population pharmacokinetics of meropenem in critically ill patients.

The pharmacokinetics of meropenem are significantly altered in critically ill patients. A population pharmacokinetic study was designed to estimate typical values of meropenem clearance in critically ill patients and evaluate potential factors of influence. After meropenem reached a steady state in each patient, two blood samples were taken within the dose interval. The one-compartment pharmacokinetic model based on the data from 101 intensive care unit patients was built using NONMEM software. Typical values of meropenem clearance and volume of distribution were 3.80 L/h and 3.52 L, respectively. In the final model, meropenem clearance was influenced by serum concentrations of creatinine (CRE), leukocyte count (WBC), hypertension (HTA), and concomitant use of vancomycin (VAN) or colistimethate (COL): CL (L/h) = 5.29 × CRE ^ 0.000001 × WBCs ^ (-0.165) + 0.000001 × HTA + 0.825 × VAN + 1.28 × COL. In order to achieve effective plasma concentrations of meropenem in critically ill patients, the meropenem dosing regimen should be adjusted according to individual values of drug clearance.

Integrating machine learning with pharmacokinetic models: Benefits of scientific machine learning in adding neural networks components to existing PK models.

Recently, the use of machine-learning (ML) models for pharmacokinetic (PK) modeling has grown significantly. Although most of the current approaches use ML techniques as black boxes, there are only a few that have proposed interpretable architectures which integrate mechanistic knowledge. In this work, we use as the test case a one-compartment PK model using a scientific machine learning (SciML) framework and consider learning an unknown absorption using neural networks, while simultaneously estimating other parameters of drug distribution and elimination. We generate simulated data with different sampling strategies to show that our model can accurately predict concentrations in extrapolation tasks, including new dosing regimens with different sparsity levels, and produce reliable forecasts even for new patients. By using a scenario of fitting PK data with complex absorption, we demonstrate that including known physiological structure into an SciML model allows us to obtain highly accurate predictions while preserving the interpretability of classical compartmental models.

Vancomycin and daptomycin dosing recommendations in patients receiving home hemodialysis using Monte Carlo simulation

BackgroundFew drug dosing recommendations for patients receiving home hemodialysis (HHD) have been published which has hindered the adoption of HHD. HHD regimens vary widely and differ considerably from conventional, thrice weekly, in-center hemodialysis in terms of treatment frequency, duration and blood and dialysate flow rates. Consequently, vancomycin and daptomycin clearances in HHD are also likely to be different, consequently HHD dosing regimens must be developed to ensure efficacy and minimize toxicity when these antibiotics are used. Many HHD regimens are used clinically, this study modeled ten common HHD regimens and determined optimal vancomycin and daptomycin dosing for each HHD regimen.MethodsMonte Carlo simulations using pharmacokinetic data derived from the literature and demographic data from a large HHD program treating patients with end stage kidney disease were incorporated into a one-compartment pharmacokinetic model. Virtual vancomycin and daptomycin doses were administered post-HHD and drug exposures were determined in 5,000 virtual patients receiving ten different HHD regimens. Serum concentration monitoring with subsequent dose changes was incorporated into the vancomycin models. Pharmacodynamic target attainment rates were determined for each studied dose. The lowest possible doses that met predefined targets in virtual patients were chosen as optimal doses.ResultsHHD frequency, total dialysate volumes and HHD durations influenced drug exposure and led to different dosing regimens to meet targets. Antibiotic dosing regimens were identified that could meet targets for 3- and 7-h HHD regimens occurring every other day or 4–5 days/week. HHD regimens with 3-day interdialytic periods required higher doses prior to the 3-day period. The addition of vancomycin serum concentration monitoring allowed for calculation of necessary dosing changes which increased the number of virtual subjects meeting pharmacodynamic targets.ConclusionsDoses of vancomycin and daptomycin that will meet desired pharmacodynamic targets in HHD are dependent on patient and HHD-specific factors. Doses used in conventional thrice weekly hemodialysis are unlikely to meet treatment goals. The antibiotic regimens paired with the HHD parameters studied in this analysis are likely to meet goals but require clinical validation.

A study of the pharmacokinetics and pharmacodynamics of oxytocin at elective caesarean delivery.

Oxytocin is widely used to prevent atonic postpartum haemorrhage after caesarean delivery. Initial treatment failure rates are high and inadequate dosing may contribute. Excessive doses, however, are associated with serious adverse effects. The pharmacokinetic data from this context are sparse and there is a lack of data in the immediate postpartum minutes after an initiating bolus. The pharmacodynamic data from this context are exclusively from dose-effect studies, with some suggesting that higher doses of oxytocin are required to provide adequate uterine tone in obese compared with non-obese women. We aimed to perform a pharmacokinetic and pharmacodynamic study that would facilitate more precise weight-based oxytocin dosing. We measured arterial oxytocin concentration, uterine tone and haemodynamic parameters in 25 women in the first 40 min after exogenous oxytocin administration at elective caesarean delivery. Serum oxytocin concentrations varied considerably between individuals. We constructed a one-compartment pharmacokinetic model of exogenous oxytocin deposition, after its administration with an initiating bolus and a maintenance infusion, at elective caesarean delivery. Body weight was evaluated as a potential covariate but was not included in the model due to lack of statistically significant reduction in the objective function. We calculated the volume of distribution and clearance (mean [coefficient of variation]) as 156.1 l [18%] and 83 ml.s-1 [32%] but found no within-individual correlation between serum oxytocin concentration and uterine tone or haemodynamic parameters. In conclusion, we observed a large variation in serum oxytocin concentrations between individuals receiving similar doses of oxytocin and were unable to establish weight-based dosing of exogenous oxytocin at caesarean delivery. Our findings suggest that future studies on oxytocin pharmacokinetics would need large sample sizes. In the absence of such data, oxytocin dosing should continue to be guided by uterine tone assessments and adjusted according to a strategy based on the best evidence from dose-effect studies.

Population pharmacokinetics of polymyxin B in patients with liver dysfunction.

Polymyxin B (PMB) is widely used to treat infections caused by multidrug-resistant Gram-negative pathogens. Currently, the pharmacokinetic data of PMB in patients with liver dysfunction are limited. This study aimed to develop a population pharmacokinetic (PopPK) model of PMB in patients with liver dysfunction and identify the factors affecting PMB pharmacokinetics. We conducted a retrospective pharmacokinetic study involving 136 adults with different levels of liver function. Nonlinear mixed effects modelling was used to develop a PopPK model of PMB. Monte Carlo simulation was used to design PMB dosage schedules across various liver and renal functions. PMB pharmacokinetic analyses included 401 steady-state concentrations in 136 adult patients. A one-compartment pharmacokinetic model with first-order absorption and elimination was used to describe the data. The typical population value of PMB clearance was 2.43 L/h and the volume of distribution was 23.11 L. This study revealed that creatinine clearance (CrCL) and Child-Pugh class were significantly associated with PMB pharmacokinetic parameters; however, clinically relevant variations of dose-normalized drug exposure were not significant. For patients with a minimum inhibitory concentration of ≤0.5mg/L, the appropriate dose was 40-75 mg/12-h. When the dose exceeded 100 mg/12-h, the risk of nephrotoxicity increased significantly. This study provided PMB pharmacokinetic information for patients with liver dysfunction. Patients with renal and liver dysfunctions may not require an initial dose adjustment. Rather than PopPK-guided dose adjustment, therapeutic drug monitoring of PMB plays a more direct role in optimizing dosing regimens based on its therapeutic window.

Recommendations of Gentamicin Dose Based on Different Pharmacokinetic/Pharmacodynamic Targets for Intensive Care Adult Patients: A Redefining Approach.

In addition to the maximum plasma concentration (Cmax) to the minimum inhibitory concentration (MIC) ratio, the 24-hour area under the concentration-time curve (AUC24h) to MIC has recently been suggested as pharmacokinetic/pharmacodynamic (PK/PD) targets for efficacy and safety in once-daily dosing of gentamicin (ODDG) in critically ill patients. This study aimed to predict the optimal effective dose and risk of nephrotoxicity for gentamicin in critically ill patients for two different PK/PD targets within the first 3 days of infection. The gathered pharmacokinetic and demographic data in critically ill patients from 21 previously published studies were used to build a one-compartment pharmacokinetic model. The Monte Carlo Simulation (MCS) method was conducted with the use of gentamicin once-daily dosing ranging from 5-10 mg/kg. The percentage target attainment (PTA) for efficacy, Cmax/MIC ~8-10 and AUC24h/MIC ≥110 targets, were studied. The AUC24h >700 mg⋅h/L and Cmin >2 mg/L were used to predict the risk of nephrotoxicity. Gentamicin 7 mg/kg/day could achieve both efficacy targets for more than 90% when the MIC was <0.5 mg/L. When the MIC increased to 1 mg/L, gentamicin 8 mg/kg/day could reach the PK/PD and safety targets. However, for pathogens with MIC ≥2 mg/L, no studied gentamicin doses were sufficient to reach the efficacy target. The risk of nephrotoxicity using AUC24h >700 mg⋅h/L was small, but the risk was greater when applying a Cmin target >2 mg/L. Considering both targets of Cmax/MIC ~8-10 and AUC24h/MIC ≥110, an initial gentamicin dose of 8 mg/kg/day should be recommended in critically ill patients for pathogens with MIC of ≤1 mg/L. Clinical validation of our results is essential.

Population Pharmacokinetic and Pharmacodynamic Analysis of Valganciclovir for Optimizing Preemptive Therapy of Cytomegalovirus Infections in Kidney Transplant Recipients.

This study aimed to develop a population pharmacokinetic/pharmacodynamic (PK/PD) model of valganciclovir for preemptive therapy of cytomegalovirus (CMV) infection in kidney transplant patients. A population PK/PD model was developed with Monolix. Ganciclovir concentrations and CMV viral loads were obtained retrospectively from kidney transplant patients receiving routine clinical care. Ten thousand Monte Carlo simulations were performed with the licensed dosages adjusted for renal function to assess the probability of attaining a viral load target of ≤290 and ≤137 IU/mL. Fifty-seven patients provided 343 ganciclovir concentrations and 328 CMV viral loads for PK/PD modeling. A one-compartment pharmacokinetic model coupled with an indirect viral turnover growth model with stimulation of viral degradation pharmacodynamic model was devised. Simulations showed that 1- and 2-log10 reduction of CMV viral load mostly occurred between a median of 5 to 6 and 12 to 16 days, respectively. The licensed dosages achieved a probability of reaching the viral load target ≥90% at days 35 to 49 and 42 to 56 for the thresholds of ≤290 and ≤137 IU/mL, respectively. Simulations indicate that in patients with an estimated glomerular filtration rate of 10 to 24 mL/min/1.73m2, a dose increase to 450 mg every 36 h may reduce time to optimal viral load target to days 42 and 49 from a previous time of 49 and 56 days for the thresholds of ≤290 and ≤137 IU/mL, respectively. Currently licensed dosages of valganciclovir for preemptive therapy of CMV infection may achieve a viral load reduction within the first 2 weeks, but treatment should continue for ≥35 days to ensure viral load suppression.

Piperacillin-tazobactam dosing in anuric acute kidney injury patients receiving continuous renal replacement therapy.

To determine appropriate dosing of piperacillin-tazobactam in critically ill patients receiving continuous renal replacement therapy (CRRT). The databases of PubMed, Embase, and ScienceDirect were searched. We used the Medical Subject Headings of "piperacillin-tazobactam," "CRRT," and "pharmacokinetics" or related terms or synonym to identify the studies for reviews. A one-compartment pharmacokinetic model was conducted to predict piperacillin levels for the initial 48 h of therapy. The pharmacodynamic target was 50% of free drug level above the minimum inhibitory concentration (MIC) and 4 times of the MIC. The dose that achieved at least 90% of the probability of target attainment was defined as an optimal dose. Our simulation study reveals that the dosing regimen of piperacillin-tazobactam 12 g/day is appropriate for treating Pseudomonal infection with KDIGO recommended effluent rate of 25-35 mL/kg/h. The MIC values of each setting were an important factor to design piperacillin-tazobactam dosing regimens. The Monte Carlo simulation can be a useful tool to evaluate drug dosing in critically ill acute kidney injury patients receiving CRRT when limited pharmacokinetic data are a concern. Clinical validation of these results is needed.

Adequacy of cefepime concentrations in the early phase of critical illness: A case for precision pharmacotherapy.

In critically ill patients, adequacy of early antibiotic exposure has been incompletely evaluated. This study characterized factors associated with inadequate cefepime exposure in the first 24 h of critical illness. Prospective cohort study. Academic Medical Center. Critically ill adults treated with cefepime. Patients with acute kidney injury or treated with kidney replacement therapy or extracorporeal membrane oxygenation were excluded. None. A nonlinear mixed-effects pharmacokinetic (PK) model was developed to estimate cefepime concentrations for each patient over time. The percentage of time the free drug concentration exceeded 8 mg/L during the first 24 h of therapy was calculated (%ƒT>8; appropriate for the susceptible breakpoint for Pseudomonas aeruginosa). Factors predictive of low %ƒT>8 were explored with multivariable regression. In the 100 included patients, a one-compartment PK model was developed with first-order elimination with covariates for weight and estimated glomerular filtration rate based on creatinine and cystatin C (eGFRSCr-CysC). The median (interquartile range) %ƒT>8 for cefepime in the first 24 h of therapy based on this model was 85% (66%, 100%). Less than 100% ƒT>8 during first 24 h of therapy occurred in 70 (70%) individuals. Lower Sequential Organ Failure Assessment score (p = 0.032) and higher eGFRSCr-CysC (p< 0.001) predicted a lower %ƒT>8. Central nervous system infection source was protective (i.e., associated with a higher %ƒT>8; p = 0.008). During early critical illness, cefepime concentrations were inadequate in a significant proportion of patients. Antimicrobial optimization is needed to improve the precision of pharmacotherapy in the critically ill patients.

Evaluation of treosulfan cumulative exposure in paediatric patients through population pharmacokinetics and dosing simulations.

To investigate the pharmacokinetics (PK) of intravenous treosulfan in paediatric patients undergoing haematopoietic stem cell transplantation (HSCT) for a broad range of diseases and to explore the impact of different dosing regimens on treosulfan exposure (area under the concentration-time curve, AUC0→∞ ) through dosing simulations. A prospective multicentre PK study was conducted using treosulfan concentration data (n = 423) collected from 53 children (median age 3.5, range 0.2-17.0years) receiving three daily age-guided doses (10-14 g/m2 ). Population PK modelling was performed using NONMEM software, utilising a stepwise forward selection backward elimination method and likelihood-ratio test for screening covariates to describe PK variability. Monte Carlo simulation was used to generate patient PK data for 10 000 virtual paediatric patients and cumulative AUC0→∞ values were evaluated using age, body surface area (BSA) and model-based dosing regimens, targeting 4800 mg*h/L. Treosulfan concentration data were described using a one-compartment PK model with first-order elimination. Population mean (95% CI) estimates for clearance (CL) and volume of distribution (V) were 16.3 (14.9-18.1) L/h and 41.9 (38.8-45.1) L, respectively. Allometrically scaled body weight was the best covariate descriptor for CL and V, and maturational age further explained variability in CL. Dosing simulations indicated that in young patient groups (<2years), a model-based dosing regimen more accurately achieved the target AUC0→∞ (58.3%) over the age (42.6%) and BSA-based (51.3%) regimens. Treosulfan disposition was described through allometric body weight and maturational age descriptors. Model-informed dosing is recommended for patients under 2years. Treosulfan PK parameters and AUC0→∞ were not influenced by patient disease.

Population pharmacokinetics and dosing optimization of unbound teicoplanin in Chinese adult patients.

Objectives: To develop a population pharmacokinetic (PopPK) model describing unbound teicoplanin concentrations in Chinese adult patients and perform Monte Carlo simulations to optimize the dosing regimens. Methods: The raw data for PopPK analysis in this study were collected from Chinese adult patients. A PopPK model of unbound teicoplanin was developed and Monte Carlo simulations were used to optimize the dosing regimens. The trough concentrations of unbound teicoplanin were targeted at 0.75mg/L and 1.13mg/L for most infection induced by Gram-positive bacteria and endocarditis or severe infections, respectively. Results: A total of 103 teicoplanin unbound concentrations were collected from 72 Chinese adult patients. A one-compartment pharmacokinetic model with first-order elimination was established. The typical values of clearance and the volume of distribution were 11.7L/h and 811L, respectively. The clearance and volume of distribution of unbound teicoplanin were positively correlated with estimated glomerular filtration rate (eGFR) and serum albumin concentrations, respectively. Dosing simulation results showed that standard dosing regimens were unable to meet the treatment needs of all patients, and the dosing regimen need optimize based on eGFR and serum albumin concentrations. The high eGFR and serum albumin concentration were associated with reduced probability of achieving target unbound trough concentrations. Conclusion: We successfully characterized the pharmacokinetics of unbound teicoplanin in Chinese adult patients. Importantly, we further highlight the importance of guiding dosing through unbound drugs. To achieve safe and effective treatment, the dosing regimens need to be adjusted according to eGFR and serum albumin concentrations.

Pharmacokinetics of Myo-Inositol in a Wistar Rat Animal Model.

Myo-inositol is the most popular inositol in living organisms, where it is present as a sugar alcohol, in a free form, and can also be described as a lipid. The aim of this study was to check the concentration change of a myo-inositol solution from the time of oral administration and over a 48 h period in Wistar-type rats. All rats received 2 g/kg of inositol as a solution in distilled water by oral gavage. Estimated parameters were based on the serum concentration of myo-inositol observed in nine individual rats with regard to time. Observations were described as a one-compartment pharmacokinetic model with first-order absorption and zero-order endogenous input of checked inositol. The highest myo-inositol concentration was observed in the first hour after oral administration in the serum of all tested rats. Then, the concentration began decreasing immediately after the maximal peak. The inositol concentration continued to decrease, but after 24 h its level was still higher than before the administration. The plasma profile of the myo-inositol concentration showed a rapid decline over time, possibly due to the metabolism of this compound.

An Analytical Approach of One-Compartmental Pharmacokinetic Models with Sigmoidal Hill Elimination.

In this study, we aim to develop the analytical solutions of one-compartment pharmacokinetic models with sigmoidal Hill elimination and quantitatively revisit some widely used pharmacokinetic indexes. For this purpose, we have first established the closed-form solutions of the model with intravenous bolus administration through introducing a transcendent H function, which is proved a generalized form of the Lambert W function. Then, in the case of a single dose, we have obtained the explicit formulas for several pharmacokinetic surrogates, such as the clearance, elimination half-life and partial/total drug exposure. All these surrogates are found concentration-dependent and sensitive to the Hill coefficient [Formula: see text]. Meanwhile, in establishing the closed-form formulas for multiple repeated dosing regimens, we have discovered phase transitions for steady states with different ranges of [Formula: see text] in function of the lengths of dosing intervals. Further, our results are illustrated with two drug examples. To conclude, the present findings elucidate the intrinsic quantitative structural properties of pharmacokinetic models with Hill elimination and provide new knowledge for nonlinear pharmacokinetics and guidance for rational drug designs.

An Artificial Gut/Absorption Simulator: Description, Modeling, and Validation Using Caffeine.

The purpose of this study was to develop and validate a simultaneous dissolution and absorption testing tool, the "artificial gut simulator" (AGS), for oral drug formulations. The AGS was constructed using hollow fibers and housed in a 3-mL UV spectrophotometric cuvette that provided a large surface area-to-volume ratio to simulate absorption at a physiological rate. A quasi-steady-state model describing absorption was developed and validated using a high aqueous solubility, BCS-I model compound, caffeine. This model was used to optimize the AGS operating parameters to simulate physiological gastric emptying and caffeine absorption, which was further input into a one-compartment pharmacokinetic (PK) model. The in vivo caffeine plasma concentration-time profiles matched those predicted by the PK model with in vitro input from the AGS. This work provides a framework for establishing an in vitro/in vivo correlation with high-permeability, BCS-II supersaturating drug formulations, which will be explored in the future studies.

Timing of Live Attenuated Vaccination in Infants Exposed to Infliximab or Adalimumab in Utero: A Prospective Cohort Study in 107 Children.

For infants exposed in utero to anti-tumour necrosis factor-α [TNF] medications, it is advised that live-attenuated vaccinations be postponed until the drug is cleared, but little is known about time to clearance. To minimize delays before live-attenuated vaccination can be given, we aimed to develop a pharmacokinetic model to predict time-to-clearance in infants exposed during pregnancy. We prospectively followed in utero infliximab/adalimumab-exposed infants of mothers with inflammatory bowel disease across four countries between 2011 and 2018. Infants with a detectable anti-TNF umbilical-cord level and at least one other blood sample during the first year of life were included. Overall, 107 infants were enrolled, including 166 blood samples from 71 infliximab-exposed infants and 77 samples from 36 adalimumab-exposed infants. Anti-TNF was detectable in 23% [n = 25] of infants at 6 months. At 12 months, adalimumab was not detected but 4% [n = 3] had detectable infliximab. A Bayesian forecasting method was developed using a one-compartment pharmacokinetic model. Model validation showed that the predicted clearing time was in accordance with the measured observations. A clinician-friendly online calculator was developed for calculating full anti-TNF clearing time: https://xiaozhu.shinyapps.io/antiTNFcalculator2/. Almost one-quarter of infants born to mothers receiving anti-TNF during pregnancy have detectable anti-TNF at 6 months. To limit the time to live-attenuated vaccination in infants of mothers receiving anti-TNF during pregnancy, the results of a cord drug level at birth and a second sample ≥ 1 month thereafter can be used to estimate the time for full anti-TNF clearance in these children.

Passive immunization against COVID-19 by anti-SARS-CoV-2 spike IgG in commercially available immunoglobulin preparations in severe antibody deficiency

Passive immunization against COVID-19 by anti-SARS-CoV-2 spike IgG in commercially available immunoglobulin preparations in severe antibody deficiency

Predicting model-informed precision dosing: A test-case in tacrolimus dose adaptation for kidney transplant recipients.

Before investing resources into the development of a precision dosing (model‐informed precision dosing [MIPD]) tool for tacrolimus, the performance of the tool was evaluated in silico. A retrospective dataset of 315 de novo kidney transplant recipients was first used to identify a one‐compartment pharmacokinetic (PK) model with time‐dependent clearance. MIPD performance was subsequently evaluated by calculating errors to predict future concentrations, which is directly related to dosing precision and probability of target attainment (PTA). Based on the identified model residual error, the theoretical upper limit was 45% PTA for a target of 13.5 ng/ml and an acceptable range of 12–15 ng/ml. Using empirical Bayesian estimation, this limit was reached on day 5 post‐transplant and beyond. By incorporating correlated within‐patient variability when predicting future individual concentrations, PTA improved beyond the theoretical upper limit. This yielded a Bayesian feedback dosing algorithm accurately predicting future trough concentrations and adapting each dose to reach a target concentration. Simulated concentration‐time profiles were then used to quantify MIPD‐based improvement on three end points: average PTA increased from 28% to 39%, median time to three concentrations in target decreased from 10 to 7 days, and mean log‐squared distance to target decreased from 0.080 to 0.055. A study of 200 patients was predicted to have sufficient power to demonstrate these nuanced PK end points reliably. These simulations supported our decision to develop a precision dosing tool for tacrolimus and test it in a prospective trial.

The Presence of Phases and the Inability of the Classical Compartment Models to Provide Pharmacokinetic Parameters of Physiological Significance for Lipophilic Drugs

The first biphasic open one-compartment pharmacokinetic model is described. Its analytical solutions to drug concentration were developed from parameters of an open two-compartment pharmacokinetic model. The model is used to explain the unusually large compartment volumes and apparent volumes of distribution of lipophilic drugs, as well as to identify which of the pharmacokinetic parameters of the classical compartment models are biologically relevant.

Population pharmacokinetics and exposure‐response modeling analyses of guselkumab in patients with psoriatic arthritis

Guselkumab is an anti‐interleukin‐23 human monoclonal antibody effective in treating psoriatic arthritis (PsA). To characterize the pharmacokinetics (PKs) and exposure‐response relationship of guselkumab in PsA, population PKs, and exposure‐response modeling, analyses were conducted using data from pivotal phase III studies of subcutaneous guselkumab in patients with PsA. The observed serum concentration‐time data of guselkumab were adequately described by a one‐compartment linear PK model with first‐order absorption and elimination. Covariates identified as contributing to the observed guselkumab PK variability were body weight and diabetes comorbidity; however, the magnitude of the effects of these covariates was not considered clinically relevant, and dose adjustment was not warranted for the patient population investigated. Positive exposure‐response relationships were demonstrated with landmark and longitudinal exposure‐response analyses between guselkumab exposure and clinical efficacy end points (American College of Rheumatology [ACR] 20%, 50%, and 70% improvement criteria and Investigator’s Global Assessment [IGA] of psoriasis) at weeks 20 and/or 24, with no clinically relevant differences observed in improvement of PsA signs and symptoms between the two guselkumab treatment regimens evaluated (100 mg every 4 weeks or 100 mg at weeks 0 and 4, then every 8 weeks). Baseline Disease Activity Score in 28 joints (DAS28), Psoriasis Area and Severity Index (PASI) score, and/or C‐reactive protein level were identified as influencing covariates on guselkumab exposure‐response model parameters. These results provide a comprehensive evaluation of subcutaneous guselkumab PKs and exposure‐response relationship that supports the dose regimen of 100 mg at weeks 0 and 4, then every 8 weeks in patients with PsA.