Matthew M. Riggs

Multiscale Physiology‐Based Modeling of Mineral Bone Disorder in Patients With Impaired Kidney Function

A physiologically based, multiscale model of calcium homeostasis and bone remodeling was used to describe the impact of progressive loss of kidney function over a typical 10‐year course of chronic kidney disease (CKD), including the evolution of secondary hyperparathyroidism (HPT) caused by diminished renal phosphate clearance and increased plasma phosphate. An important sequela of HPT is marked elevations in bone resorption and loss of bone mineral density (BMD). Clinically, this CKD‐related disease state is described as mineral bone disorder, or CKD‐MBD. A multiscale physiologic model previously had been shown to describe CKD‐MBD‐related clinical changes in phosphate, parathyroid hormone (PTH), and calcitriol. The authors have extended the model to link bone remodeling markers with BMD elimination (0.000145 h−1) and formation rates. The composite model predicted lumbar spine BMD losses, relative to baseline, at months 28 (glomerular filtration rate = 58 mL/min), 50 (39 mL/min), and 120 (16 mL/min) of approximately −0.98%, −3.0%, and −6.5%, respectively, compared to the observed BMD values in corresponding renal function groups, scaled to a 100‐mL/min baseline, of −0.5%, −4.0%, and −8.1%, respectively. In addition, simulated interventions with a hypothetical calcimimetic agent and calcitriol are provided to show the utility of this model as a platform for evaluating therapeutics.

Population pharmacokinetics of empagliflozin, a sodium glucose cotransporter 2 inhibitor, in patients with type 2 diabetes

Data from five randomized, placebo‐controlled, multiple oral dose studies of empagliflozin in patients with type 2 diabetes mellitus (T2DM; N = 974; 1–100 mg q.d.; ≤12 weeks) were used to develop a population pharmacokinetic (PK) model for empagliflozin. The model consisted of two‐compartmental disposition, lagged first‐order absorption and first‐order elimination, and incorporated appropriate covariates. Population estimates (interindividual variance, CV%) of oral apparent clearance, central and peripheral volumes of distribution, and inter‐compartmental clearance were 9.87 L/h (26.9%), 3.02 L, 60.4 L (30.8%), and 5.16 L/h, respectively. An imposed allometric weight effect was the most influential PK covariate effect, with a maximum effect on exposure of ±30%, using 2.5th and 97.5th percentiles of observed weights, relative to the median observed weight. Sex and race did not lend additional description to PK variability beyond allometric weight effects, other than ∼25% greater oral absorption rate constant for Asian patients. Age, total protein, and smoking/alcohol history did not affect PK parameters. Predictive check plots were consistent with observed data, implying an adequate description of empagliflozin PKs following multiple dosing in patients with T2DM. The lack of marked covariate effects, including weight, suggests that no exposure‐based dose adjustments were required within the study population and dose range.

Facilitating pharmacometric workflow with the metrumrg package for R

metrumrg is an R package that facilitates workflow for the discipline of pharmacometrics. Support is provided for data preparation, modeling, simulation, diagnostics, and reporting. Existing tools and techniques are emphasized where available; original solutions are provided for otherwise unmet needs. In particular, metrumrg implements an R interface for the NONMEM(®) modeling software, optionally run in a distributed computing environment. The paradigm allows start-to-finish analyses in a single scripting language. Emphasis on text-based formats promotes traceability of results.

Population Pharmacokinetics and Exposure-Response of Albinterferon Alfa-2b

Albinterferon alfa‐2b (albIFN) has been studied for treatment of chronic hepatitis C virus (HCV). A population pharmacokinetics model was developed using nonlinear mixed‐effects modeling. Efficacy/safety exposure‐response relationships were assessed for subcutaneous albIFN doses (900–1800 μg once every 2 or 4 weeks) administered for either 24 weeks (HCV genotypes 2/3) or 48 weeks (genotype 1), plus daily oral ribavirin. Sustained virologic response (SVR) exposure‐response was modeled using logistic regression. Adverse event incidence was tabulated versus exposure quartiles. First‐order absorption rate constant (0.0148 h−1), apparent clearance (38.9 mL/h), and apparent volume of distribution (11.6 L) had interindividual variances (coefficient of variation) of 21%, 34%, and 24%, respectively. Residual variance estimates were 27% (coefficient of variation) and 1.51 ng/mL (standard deviation). For the only explanatory covariate—body weight—exposure decreased as weight increased. Important SVR predictors included baseline HCV RNA, fibrosis score, and black race (genotype 1); SVR was minimally related to exposure. Most adverse events had similar incidence rates across exposure quartiles. Some adverse events had a higher incidence in the upper exposure quartile without evidence of exposure‐response across the lower quartiles. Given the lack of consistent efficacy/safety exposure‐response relationships, further investigation is necessary to optimize albIFN dosing.

Exposure−response modelling for empagliflozin, a sodium glucose cotransporter 2 (SGLT2) inhibitor, in patients with type 2 diabetes

AIMS To provide model-based clinical development decision support including dose selection guidance for empagliflozin, an orally administered sodium glucose cotransporter 2 inhibitor, through developed exposure-response (E-R) models for efficacy and tolerability in patients with type 2 diabetes mellitus (T2DM). METHODS Five randomized, placebo-controlled, multiple oral dose studies of empagliflozin in patients with T2DM (n = 974; 1-100 mg once daily, duration ≤12 weeks) were used to develop E-R models for efficacy (glycosylated haemoglobin [HbA1c ], fasting plasma glucose [FPG] and urinary glucose excretion). Two studies (n = 748, 12 weeks) were used to evaluate tolerability E-R. RESULTS The efficacy model predicted maximal decreases in FPG and HbA1c of 16% and 0.6%, respectively, assuming a baseline FPG concentration of 8 mm (144 mg dl(-1) ) and 10-25 mg every day empagliflozin targeted 80-90% of these maximums. Increases in exposure had no effect on incidence rates of hypoglycaemia (n = 4), urinary tract infection (n = 17) or genital/vulvovaginal-related (n = 16) events, although low prevalence rates may have precluded more accurate evaluation. CONCLUSIONS E-R analyses indicated that 10 and 25 mg once daily empagliflozin doses achieved near maximal glucose lowering efficacy.

A Priori Identifiability of Target-Mediated Drug Disposition Models and Approximations

A priori identifiability of mathematical models assures that for a given input/output experiment, the parameter set has one unique solution within a defined space, independent of the experimental design. Many biologic therapeutics exhibit target-mediated drug disposition (TMDD), and use of the full compartmental model describing this system is well documented. In practice, estimation of the full parameter set for TMDD models, given real-world clinical data, is characterized by convergence difficulties and unstable solutions. Still, the formal assessment of the a priori identifiability of these systems has yet to be reported. The exact arithmetic rank (EAR) approach was used to test the a priori identifiability of a TMDD model as well as model approximations. The full TMDD and quasi-equilibrium/rapid binding (QE/RB), quasi-steady state (QSS), and Michaelis-Menten (MM) approximations were fully identifiable, a priori, regardless of whether observations were taken from a single or multiple compartments. The results of these identifiability analyses indicated that the difficulty with TMDD model convergence, a posteriori, lies in the experimental design, not in the mathematical identifiability in the lack of samples from several compartments. Experiments can be tailored to resolve these structurally non-identifiable parameters, notwithstanding practical implementation challenges. This work highlights the importance of identifiability analyses, specifically how they can influence experimental design and selection of the appropriate model structure to describe a dynamic biological system.

Population Pharmacokinetic– Pharmacodynamic Analysis to Characterize the Effect of Empagliflozin on Renal Glucose Threshold in Patients With Type 1 Diabetes Mellitus

Sodium glucose cotransporter 2 inhibitors increase urinary glucose excretion (UGE) by lowering the renal threshold for glucose (RTG). We aimed to quantify the effect of the sodium glucose cotransporter inhibitor empagliflozin on renal glucose reabsorption in patients with type 1 diabetes mellitus (T1DM) using a mechanistic population pharmacokinetic–pharmacodynamic (PK‐PD) model and to compare results with analyses in patients with type 2 diabetes mellitus (T2DM). The PK‐PD model was developed using data from a randomized phase 2 study in which patients with T1DM received oral once‐daily empagliflozin 2.5 mg, empagliflozin 10 mg, empagliflozin 25 mg, or placebo as an adjunct to insulin. The model assumed that UGE was dependent on plasma glucose and renal function and that empagliflozin lowered RTG. The final model was evaluated using visual predictive checks and found to be consistent with observed data. Calculated RTG with placebo was 181 mg/dL, and with empagliflozin (steady state) 1 mg and 2.5 mg was 53.4 mg/dL and 12.5 mg/dL, respectively. Empagliflozin 10 mg and 25 mg yielded negative RTG values, implying RTG was reduced to a negligible value. Although estimated PK‐PD parameters were generally comparable between patients with T1DM and patients with T2DM, slight differences were evident, leading to lower RTG and higher UGE in patients with T1DM compared with patients with T2DM. In conclusion, the model provided a reasonable description of UGE in response to administration of empagliflozin and placebo in patients with T1DM.

Population pharmacokinetics and exposure-response of trastuzumab emtansine in advanced breast cancer previously treated with ≥2 HER2-targeted regimens

AIMS We conducted population pharmacokinetic (PopPK) and exposure-response analyses for trastuzumab emtansine (T-DM1), to assess the need for T-DM1 dose optimization in patients with low exposure by using TH3RESA [A Study of Trastuzumab Emtansine in Comparison With Treatment of Physicians Choice in Patients With human epidermal growth factor receptor 2 (HER2)-positive Breast Cancer Who Have Received at Least Two Prior Regimens of HER2-directed Therapy] study data (NCT01419197). The randomized phase III TH3RESA study investigated T-DM1 vs. treatment of physicians choice (TPC) in patients with heavily pretreated HER2-positive advanced breast cancer. METHODS We compared a historical T-DM1 PopPK model with T-DM1 pharmacokinetics in TH3RESA and performed exposure-response analyses using model-predicted cycle 1 maximum concentration (Cmax ), cycle 1 minimum concentration (Cmin ) and area under the concentration-time curve at steady state (AUCss ). Kaplan-Meier analyses [overall survival (OS), progression-free survival (PFS)] and logistic regression [overall response rate (ORR), safety] were stratified by T-DM1 exposure metrics. Survival hazard ratios (HRs) in the lowest exposure quartile (Q1) of cycle 1 Cmin were compared with matched TPC-treated patients. RESULTS T-DM1 concentrations in TH3RESA were described well by the historical PopPK model. Patients with higher cycle 1 Cmin and AUCss exhibited numerically longer median OS and PFS and higher ORR than patients with lower exposure. Exposure-response relationships were less evident for cycle 1 Cmax . No relationship between exposure and safety was identified. HRs for the comparison of T-DM1-treated patients in the Q1 subgroup with matched TPC-treated patients were 0.96 [95% confidence interval (CI) 0.63, 1.47] for OS and 0.92 (95% CI 0.64, 1.32) for PFS. CONCLUSIONS Exposure-response relationships for efficacy were inconsistent across exposure metrics. HRs for survival in patients in the lowest T-DM1 exposure quartile vs. matched TPC-treated patients suggest that, compared with TCP, the approved T-DM1 dose is unlikely to be detrimental to patients with low exposure.