Assessment of the Impact of Renal Impairment on Systemic Exposure of New Molecular Entities: Evaluation of Recent New Drug Applications

Disposition and clinical implications of protein-bound uremic toxins

In patients with chronic kidney disease (CKD), adequate renal clearance is compromised, resulting in the accumulation of a plethora of uremic solutes. These uremic retention solutes, also named uremic toxins, are a heterogeneous group of organic compounds with intrinsic biological activities, many of which are too large to be filtered and/or are protein bound. The renal excretion of protein-bound toxins depends largely on active tubular secretion, which shifts the binding and allows for active secretion of the free fraction. To facilitate this process, renal proximal tubule cells are equipped with a range of transporters that co-operate in basolateral uptake and luminal excretion. Many of these transporters have been characterized as mediators of drug disposition, but have recently been recognized for their importance in the proximal renal tubular transport of uremic toxins as well. This also indicates that during uremia, drug disposition may be severely affected as a result of drug–uremic toxin interaction. In addition, CKD patients receive various drugs to treat their complications potentially resulting in drug–drug interactions (DDIs), also for drugs that are non-renally excreted. This review discusses the current knowledge on formation, disposition and removal of protein-bound uremic toxins. Furthermore, implications associated with drug treatment in kidney failure, as well as innovative renal replacement therapies targetting the protein-bound uremic toxins are being discussed. It will become clear that the complex problems associated with uremia warrant a transdisciplinary approach that unites research experts in the area of fundamental biomedical research with their colleagues in clinical nephrology.

Application of Physiologically Based Pharmacokinetic Modeling to the Understanding of Bosutinib Pharmacokinetics: Prediction of Drug-Drug and Drug-Disease Interactions

Bosutinib is an orally available Src/Abl tyrosine kinase inhibitor indicated for the treatment of patients with Philadelphia chromosome-positive chronic myelogenous leukemia. Bosutinib is predominantly metabolized by CYP3A4 as the primary clearance mechanism. The main objectives of this study were to 1) develop physiologically based pharmacokinetic (PBPK) models of bosutinib; 2) verify and refine the PBPK models based on clinical study results of bosutinib single-dose drug-drug interaction (DDI) with ketoconazole and rifampin, as well as single-dose drug-disease interaction (DDZI) in patients with renal and hepatic impairment; 3) apply the PBPK models to predict DDI outcomes in patients with weak and moderate CYP3A inhibitors; and 4) apply the PBPK models to predict DDZI outcomes in renally and hepatically impaired patients after multiple-dose administration. Results showed that the PBPK models adequately predicted bosutinib oral exposures in patients after single- and multiple-dose administrations. The PBPK models also reasonably predicted changes in bosutinib exposures in the single-dose DDI and DDZI results, suggesting that the PBPK models were sufficiently developed and verified based on the currently available data. Finally, the PBPK models predicted 2- to 4-fold increases in bosutinib exposures by moderate CYP3A inhibitors, as well as comparable increases in bosutinib exposures in renally and hepatically impaired patients between single- and multiple-dose administrations. Given the challenges in conducting numerous DDI and DDZI studies of anticancer drugs in patients, we believe that the PBPK models verified in our study would be valuable to reasonably predict bosutinib exposures under various scenarios that have not been tested clinically.

Update and trends on pharmacokinetic studies in patients with impaired renal function: practical insight into application of the FDA and EMA guidelines

INTRODUCTION

The incidence of kidney dysfunction increases with age and is highly prevalent among patients with hypertension. Since many therapeutic compounds are primarily eliminated through the kidneys, impaired renal function can have negative consequences on drug disposition, efficacy and safety. Therefore, regulatory agencies such as the Food and Drug Administration (FDA) and European Medicines Agency (EMA) have issued detailed guidelines for new drug applications to determine posology requirements for patients with renal impairment. Areas covered: The current review highlights and contrasts agency requirements for pharmacokinetic renal impairment clinical studies. While many of the guidelines are similar among the two agencies, glomerular filtration rate (GFR) determination and reporting differ. Design considerations for a reduced, full or dialysis renal impairment study, as well as modifications to the FDA's draft guidance are discussed. Furthermore, scenarios where pharmacokinetic modelling analysis can benefit a drug development program are also reviewed. Moreover, practical solutions for patient recruitment challenges are addressed. Expert commentary: We summarize how 'one size does not fit all' for GFR assessment, and recommend when to use certain modalities. Finally, we highlight the need for the pharmaceutical industry to engage therapeutic experts to assist in protocol development for renal impairment studies, as these experts understand the nuances of this special population and recommended guidelines.

Strength of evidence for labeled dosing recommendations in renal impairment

BACKGROUND/AIMS

Renally excreted medications often require dose adjustment in patients with kidney impairment. While drug development and approval in the United States are typically based on several Phase I and II studies and one or more larger Phase III randomized trials, the basis for labeled dosing recommendations for patients with renal impairment is less well known. In response, we aimed to quantify the level of evidence used to recommend labeled dosing adjustments for newly approved drugs in patients with renal impairment.

METHODS

We reviewed publicly available drug labels and approval packages for new molecular entities approved in the United States between 2012 and 2014. The sample was restricted to 29 renally excreted new molecular entities that were not granted orphan drug status. We extracted data regarding approved indications, normal dosing, dosing adjustments for patients with mild (estimated glomerular filtration rate >60 mL/min/1.73 m²), moderate (estimated glomerular filtration rate 30-<60 mL/min/1.73 m²), and severe (estimated glomerular filtration rate <30 mL/min/1.73 m²) renal impairment, characteristics of studies used to justify dosing adjustments, and numbers of subjects in each study.

RESULTS

In all, 14 of 29 (48%) new molecular entities had labels that recommended dosing adjustments for patients with mild, moderate, and/or severe renal impairment. Among these 14 new molecular entities, 4 (29%) used only pharmacokinetic studies to justify the recommendations, with no examination of clinical outcomes for patients with renal impairment. Where data were available, the median number of patients with renal impairment evaluated in studies used for dosing adjustment was 34 (range, 4-5976). Of the 15 new molecular entities with no recommended dosing adjustments for this population, 2 (13%) did not report assessing the effects of renal impairment.

CONCLUSION

Nearly half of newly approved renally excreted drugs include dosing adjustments for kidney impairment on the label, but the recommendations are usually based on very small numbers of patients and often utilize pharmacokinetic studies alone. More research is needed to understand the benefits and risks of new drugs in patients with renal impairment.

A phase I pharmacokinetic and safety study of cabazitaxel in adult cancer patients with normal and impaired renal function

PURPOSE

Limited data are available on cabazitaxel pharmacokinetics in patients with renal impairment. This open-label, multicenter study assessed cabazitaxel in patients with advanced solid tumors and normal or impaired renal function.

METHODS

Cohorts A (normal renal function: creatinine clearance [CrCL] >80 mL/min/1.73 m²), B (moderate renal impairment: CrCL 30 to <50 mL/min/1.73 m²) and C (severe impairment: CrCL <30 mL/min/1.73 m²) received cabazitaxel 25 mg/m² (A, B) or 20 mg/m² (C, could be escalated to 25 mg/m²), once every 3 weeks. Pharmacokinetic parameters and cabazitaxel unbound fraction (F _U) were assessed using linear regression and mixed models. Geometric mean (GM) and GM ratios (GMRs) were determined using mean CrCL intervals (moderate and severe renal impairment: 40 and 15 mL/min/1.73 m²) versus a control (90 mL/min/1.73 m²).

RESULTS

Overall, 25 patients received cabazitaxel (median cycles: 3 [range 1-20]; Cohort A: 5 [2-13]; Cohort B: 3 [1-15]; and Cohort C: 5 [1-20]), of which 24 were eligible for pharmacokinetic analysis (eight in each cohort). For moderate and severe renal impairment versus normal renal function, GMR estimates were: clearance normalized to body surface area (CL/BSA) 0.95 (90% CI 0.80-1.13) and 0.89 (0.61-1.32); area under the curve normalized to dose (AUC/dose) 1.06 (0.88-1.27) and 1.14 (0.76-1.71); and F _U 0.99 (0.94-1.04) and 0.97 (0.87-1.09), respectively. Estimated slopes of linear regression of log parameters versus log CrCL (renal impairment) were: CL/BSA 0.06 (-0.15 to 0.28); AUC/dose -0.07 (-0.30 to 0.16); and F _U 0.02 (-0.05 to 0.08). Cabazitaxel safety profile was consistent with previous reports.

CONCLUSIONS

Renal impairment had no clinically meaningful effect on cabazitaxel pharmacokinetics.

A pharmacokinetics and safety phase 1/1b study of oral ixazomib in patients with multiple myeloma and severe renal impairment or end-stage renal disease requiring haemodialysis

Renal impairment (RI) is a major complication of multiple myeloma (MM). This study aimed to characterize the single-dose pharmacokinetics (PK) of the oral proteasome inhibitor, ixazomib, in cancer patients with normal renal function [creatinine clearance (CrCl) ≥90 ml/min; n = 20), severe RI (CrCl <30 ml/min; n = 14), or end-stage renal disease requiring haemodialysis (ESRD; n = 7). PK and adverse events (AEs) were assessed after a single 3 mg dose of ixazomib. Ixazomib was highly bound to plasma proteins (~99%) in all renal function groups. Unbound and total systemic exposures of ixazomib were 38% and 39% higher, respectively, in severe RI/ESRD patients versus patients with normal renal function. Total ixazomib concentrations were similar in pre- and post-dialyser samples collected from ESRD patients; therefore, ixazomib can be administered without regard to haemodialysis timing. Except for anaemia, the incidence of the most common AEs was generally similar across groups, but grade 3 and 4 AEs were more frequent in the severe RI/ESRD groups versus the normal group (79%/57% vs. 45%), as were serious AEs (43%/43% vs. 15%). The PK and safety results support a reduced ixazomib dose of 3 mg in patients with severe RI/ESRD.

Pharmacokinetics and safety of olodaterol administered with the Respimat Soft Mist inhaler in subjects with impaired hepatic or renal function

Purpose

In two trials, the influences of hepatic and renal impairment on the pharmacokinetics of olodaterol, a novel long-acting inhaled β₂-agonist for treatment of COPD, were investigated.

Subjects and methods

The first trial included eight subjects with mild hepatic function impairment (Child–Pugh A), eight subjects with moderate impairment (Child–Pugh B), and 16 matched healthy subjects with normal hepatic function. The second trial included eight subjects with severe renal impairment (creatinine clearance <30 mL·min⁻¹) and 14 matched healthy subjects with normal renal function. Subjects received single doses of 20 or 30 μg olodaterol administered with the Respimat Soft Mist inhaler.

Results

Olodaterol was well tolerated in all subjects. The geometric mean ratios and 90% confidence intervals of dose-normalized area under the plasma concentration-time curve from time zero to 4 hours (AUC_0–4) for subjects with mild and moderate hepatic impairment compared to healthy subjects were 97% (75%–125%) and 105% (79%–140%), respectively. Corresponding values for dose-normalized maximum concentration (C_max) were 112% (84%–151%) (mild impairment) and 99% (73%–135%) (moderate impairment). The geometric mean ratio (90% confidence interval) of AUC_0–4 for subjects with severe renal impairment compared to healthy subjects was 135% (94%–195%), and for C_max was 137% (84%–222%). There was no significant relationship between creatinine clearance and AUC_0–4 or C_max. Renal clearance of olodaterol was reduced to 20% of normal in severe renal impairment.

Conclusion

Mild to moderate hepatic function impairment or severe renal function impairment did not result in a clinically relevant increase of olodaterol systemic exposure after a single inhaled dose.

Systematic and quantitative assessment of the effect of chronic kidney disease on CYP2D6 and CYP3A4/5

Recent reviews suggest that chronic kidney disease (CKD) can affect the pharmacokinetics of nonrenally eliminated drugs, but the impact of CKD on individual elimination pathways has not been systematically evaluated. In this study we developed a comprehensive dataset of the effect of CKD on the pharmacokinetics of CYP2D6‐ and CYP3A4/5‐metabolized drugs. Drugs for evaluation were selected based on clinical drug–drug interaction (CYP3A4/5 and CYP2D6) and pharmacogenetic (CYP2D6) studies. Information from dedicated CKD studies was available for 13 and 18 of the CYP2D6 and CYP3A4/5 model drugs, respectively. Analysis of these data suggested that CYP2D6‐mediated clearance is generally decreased in parallel with the severity of CKD. There was no apparent relationship between the severity of CKD and CYP3A4/5‐mediated clearance. The observed elimination‐route dependency in CKD effects between CYP2D6 and CYP3A4/5 may inform the need to conduct clinical CKD studies with nonrenally eliminated drugs for optimal use of drugs in patients with CKD.

CYP3A5 polymorphism affects the increase in CYP3A activity after living kidney transplantation in patients with end stage renal disease

AIMS

It has been reported that cytochrome P450 (CYP)3A activity increases significantly in patients with end stage renal disease (ESRD) after kidney transplantation, with wide interindividual variability in the degree of increase. The aim of this study was to evaluate the influence of CYP3A5 polymorphism on the increase in CYP3A activity after living kidney transplantation, by measuring the plasma concentration of 4β-hydroxycholesterol.

METHODS

This prospective study recruited 22 patients with ESRD who underwent a first living kidney allograft transplantation, comprising 12 patients with CYP3A5*1 allele (CYP3A5*1/*1 or *1/*3) and 10 patients without CYP3A5*1 allele (CYP3A5*3/*3).

RESULTS

No significant difference in estimated glomerular filtration rate over time was observed between patients with the CYP3A5*1 allele and patients without the CYP3A5*1 allele, suggesting that the degrees of recovery in renal function after living kidney transplantation were similar in the two groups. However, plasma concentrations of 4β-hydroxycholesterol on days 90 (57.1 ± 13.4 vs. 39.5 ± 10.8 ng ml(-1)) and 180 (55.0 ± 14.5 vs. 42.4 ± 12.6 ng ml(-1)) after living kidney transplantation were significantly higher in the presence of the CYP3A5*1 allele than in the absence of the CYP3A5*1 allele [P = 0.0034 (95% confidence interval of difference 6.55, 28.6) and P = 0.043 (95% confidence interval of difference 0.47, 24.8), respectively], suggesting that CYP3A activity may increase markedly associated with recovery of renal function in patients with the CYP3A5*1 allele.

CONCLUSIONS

These findings suggest that the presence of the CYP3A5*1 allele contributes to marked elevation of CYP3A activity associated with recovery of renal function after kidney transplantation.

Population pharmacokinetic modeling and simulation for assessing renal impairment effect on the pharmacokinetics of mirogabalin

A population pharmacokinetic model was developed to describe plasma concentrations of mirogabalin and lactam metabolite, obtained following a single oral dose of 5 mg mirogabalin to subjects with varying degrees of renal function.A 2-compartment model was used for both mirogabalin and lactam metabolite. Body weight was a significant covariate on volume of distribution of mirogabalin and lactam metabolite, whereas creatinine clearance significantly affected both renal and nonrenal clearance of mirogabalin. The total clearance of mirogabalin was decreased by 25%, 54%, and 76% in subjects with mild, moderate, and severe renal impairment, respectively, relative to normal controls. Simulation results showed that in comparison with the normal renal function group receiving mirogabalin 15 mg once or twice daily, dose reduction by 50% or 75% in subjects with moderate or severe renal impairment would produce similar AUCss values, but 37%-43% or 28%-32% lower Cmax,ss of mirogabalin. Predicted mirogabalin AUCss was 26% higher, whereas Cmax,ss was similar in subjects with mild renal impairment compared with those having normal renal function taking the same dose. Results support a dose reduction by 50% or 75% in subjects with moderate or severe renal impairment. No dose adjustment seemed necessary for subjects with mild renal impairment.

The pharmacokinetics and safety of darapladib in subjects with severe renal impairment

AIM

Darapladib is a potent and reversible orally active inhibitor of lipoprotein-associated phospholipase A2 (Lp-PLA2 ). The aim of the study was to assess the effects of severe renal impairment on the pharmacokinetics and safety/tolerability of darapladib compared with normal renal function.

METHODS

This was an open label, parallel group study of darapladib following 10 day once daily 160 mg oral dosing in subjects with normal (n = 8) and severe renal impairment (estimated glomerular filtration rate <30 ml min(-1) 1.73 m(-2) , n = 8). Plasma concentrations of total and unbound darapladib as well as total darapladib metabolites were determined in samples obtained over 24 h on day 10.

RESULTS

Plasma concentrations of total and unbound darapladib as well as all three metabolites were higher in subjects with severe renal impairment. Area under the plasma concentration vs. time curve between time zero and 24 h (AUC(0,24 h) and maximum plasma concentration (Cmax ) of total darapladib in severely renally impaired subjects were 52% and 59% higher than those in the matched healthy subjects, respectively. Similar results were found with the darapladib metabolites. Darapladib was highly plasma protein bound with 0.047% and 0.034% unbound circulating in plasma in severely renally impaired and healthy subjects, respectively. Unbound plasma darapladib exposures were more than two-fold higher in severely renally impaired subjects than in healthy controls. Adverse events (AE) were reported in 38% of healthy subjects and 75% of severely renally impaired subjects, most of which were mild or moderate in intensity.

CONCLUSIONS

The results of this study showed that darapladib exposure was increased in subjects with severe renal impairment compared with healthy controls. However, darapladib was generally well tolerated in both groups.

Renal dosing in high-risk populations

In patients with diminished kidney function, the pharmacokinetics of many medications are altered. Alterations in absorption, distribution, and metabolism are observed in addition to altered elimination through the kidney. Classes of intravenous medications in which dose modifications are frequently required for patients with diminished kidney function include antibiotics, some anticoagulants, and chemotherapy agents. Failure to follow renal dose adjustment recommendations can lead to an increased risk of toxicity. Equations frequently used to estimate kidney function for the purpose of making renal dose adjustments include the Cockcroft-Gault, Modification of Diet in Renal Disease (MDRD), and Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations.

Inflammation-induced phenoconversion of polymorphic drug metabolizing enzymes: hypothesis with implications for personalized medicine

Phenoconversion transiently converts genotypic extensive metabolizers (EMs) into phenotypic poor metabolizers (PMs) of drugs, potentially with corresponding changes in clinical response. This phenomenon, typically resulting from coadministration of medications that inhibit certain drug metabolizing enzymes (DMEs), is especially well documented for enzymes of the cytochrome P450 family. Nonclinical evidence gathered over the last two decades also strongly implicates elevated levels of some proinflammatory cytokines, released during inflammation, in down-regulation of drug metabolism, especially by certain DMEs of the P450 family, thereby potentially causing transient phenoconversion. Clinically, phenoconversion of NAT2, CYP2C19, and CYP2D6 has been documented in inflammatory conditions associated with elevated cytokines, such as human immunodeficiency virus infection, cancer, and liver disease. The potential of other inflammatory conditions to cause phenoconversion has not been studied but experimental and anecdotal clinical evidence supports infection-induced down-regulation of CYP1A2, CYP3A4, and CYP2C9 as well. Collectively, the evidence supports a hypothesis that certain inflammatory conditions associated with elevated proinflammatory cytokines may cause phenoconversion of certain DMEs. Since inflammatory conditions associated with elevated levels of proinflammatory cytokines are highly prevalent, phenoconversion of genotypic EM patients into transient phenotypic PMs may be more frequent than appreciated. Since drug pharmacokinetics, and therefore the clinical response, is influenced by DME phenotype rather than genotype per se, phenoconversion (whatever its cause) can have a significant impact on the analysis and interpretation of genotype-focused clinical outcome association studies. There is a risk that focusing on genotype alone may miss important associations between clinical outcomes and DME phenotypes, thus compromising future prospects of personalized medicine.

Effect of hepatic or renal impairment on the pharmacokinetics of canagliflozin, a sodium glucose co-transporter 2 inhibitor

PURPOSE

Canagliflozin is a sodium-glucose cotransporter 2 inhibitor approved for the treatment of type 2 diabetes mellitus (T2DM). Because T2DM is often associated with renal or hepatic impairment, understanding the effects of these comorbid conditions on the pharmacokinetics of canagliflozin, and further assessing its safety, in these special populations is essential. Two open-label studies evaluated the pharmacokinetics, pharmacodynamics (renal study only), and safety of canagliflozin in participants with hepatic or renal impairment.

METHODS

Participants in the hepatic study (8 in each group) were categorized based on their Child-Pugh score (normal hepatic function, mild impairment [Child-Pugh score of 5 or 6], and moderate impairment [Child-Pugh score of 7-9]) and received a single oral dose of canagliflozin 300 mg. Participants in the renal study (8 in each group) were categorized based on their creatinine clearance (CLCR) (normal renal function [CLCR ≥80 mL/min]; mild [CLCR 50 to <80 mL/min], moderate [CLCR 30 to <50 mL/min], or severe [CLCR <30 mL/min] renal impairment; and end-stage renal disease [ESRD]) and received a single oral dose of canagliflozin 200 mg; the exception was those with ESRD, who received 1 dose postdialysis and 1 dose predialysis (10 days later). Canagliflozin's pharmacokinetics and pharmacodynamics (urinary glucose excretion [UGE] and renal threshold for glucose excretion [RTG]) were assessed at predetermined time points.

FINDINGS

Mean maximum plasma concentration (Cmax) and area under the plasma concentration-time curve from time zero to infinite (AUC)0-∞ values differed by <11% between the group with normal hepatic function and those with mild and moderate hepatic impairment. In the renal study, the mean Cmax values were 13%, 29%, and 29% higher and the mean AUC0-∞ values were 17%, 63%, and 50% higher in participants with mild, moderate, and severe renal impairment, respectively; values were similar in the ESRD group relative to the group with normal function, however. The amount of UGE declined as renal function decreased, whereas RTG was not suppressed to the same extent in the moderate to severe renal impairment groups (mean RTG, 93-97 mg/dL) compared with the mild impairment and normal function groups (mean RTG, 68-77 mg/dL).

IMPLICATIONS

Canagliflozin's pharmacokinetics were not affected by mild or moderate hepatic impairment. Systemic exposure to canagliflozin increased in the renal impairment groups relative to participants with normal renal function. Pharmacodynamic response to canagliflozin, measured by using UGE and RTG, declined with increasing severity of renal impairment. A single oral dose of canagliflozin was well tolerated by participants in both studies. ClinicalTrials.gov identifiers: NCT01186588 and NCT01759576.

Consequences of renal failure on non-renal clearance of drugs

Kidney disease not only alters the renal elimination but also the non-renal disposition of drugs that are metabolized by the liver. Indeed, modifications in the expression and activity of intestinal and hepatic drug metabolism enzymes and uptake and efflux transporters have been reported. Accumulated uremic toxins, inflammatory cytokines, and parathyroid hormones may modulate these proteins either directly or by inhibiting gene expression. This can lead to important unintended variations in exposure and response when drugs are administered without dose adjustment for reduced renal function. This review summarizes our current understanding of non-renal clearance in circumstances of chronic and acute renal failure with experimental but also clinical studies. It also evaluates the clinical impact on drug disposition. Predicting the extent of the drug disposition modification is difficult first because of the complex interplay between metabolic enzymes and transport proteins but also because of the differential effects in the different organs (liver, intestines). Recommendations of the US FDA are presented as they may be potentially helpful tools to predict these modifications when no specific pharmacokinetic studies are available.

Effect of renal impairment and haemodialysis on the pharmacokinetics of gemigliptin (LC15-0444)

This study evaluated the effects of renal impairment (RI) and haemodialysis (HD) on the pharmacokinetics of gemigliptin, a novel dipeptidyl peptidase-4 (DPP-4) inhibitor. After a 100 mg administration to subjects with normal renal function (n = 23) or RI (n = 24), plasma, urine or dialysate samples were analysed. Control subjects were matched to patients based on age, gender and body mass index. Patients with mild, moderate, severe RI and end-stage renal disease (ESRD) showed 1.20, 2.04, 1.50 and 1.66-fold (1.10, 1.49, 1.22 and 1.21-fold) increase of mean area under the time-plasma concentration curve from 0 to infinity (AUCinf) [maximum plasma concentration (Cmax)] of gemigliptin, respectively. Pharmacokinetics of gemigliptin was comparable between HD and non-HD periods in ESRD patients. Less than 4% of the dose was removed by 4 h HD. RI appeared to have modest effect on the gemigliptin disposition. No dose adjustment in patients with RI is proposed on the basis of exposure-response relationship. Impact of HD on the removal of gemigliptin was negligible.

Pharmacokinetic considerations in chronic kidney disease and patients requiring dialysis

INTRODUCTION

Chronic kidney disease (CKD) is the progressive decline in renal function over time. Patients with end-stage renal disease require renal replacement therapy such as hemodialysis to support life. Hemodialysis patients require several medications to treat a variety of comorbid conditions. Polypharmacy accompanied by alterations in the pharmacokinetics of medications places hemodialysis patients at increased risk of drug accumulation and adverse events.

AREAS COVERED

We review alterations in the pharmacokinetics of drugs in hemodialysis patients. The major areas of pharmacokinetics, absorption, distribution, metabolism and excretion, are covered and, where appropriate, differences between dialysis patients and non-dialysis CKD patients are compared. In addition, we review the importance of drug dialyzability and its potential impact on drug efficacy. Finally, we describe important clinical examples demonstrating nonrenal drug clearance is significantly altered in CKD.

EXPERT OPINION

Decreases in renal drug excretion experienced by hemodialysis patients have been known for years. Recent animal and human clinical pharmacokinetic studies have highlighted that nonrenal clearance of drugs is also substantially decreased in CKD. Clinical pharmacokinetic studies are required to determine the optimal dosage of drugs in CKD and hemodialysis patients in order to decrease the incidence of adverse medication events in these patient populations.

Application of a physiologically based pharmacokinetic model informed by a top-down approach for the prediction of pharmacokinetics in chronic kidney disease patients

Quantitative prediction of the impact of chronic kidney disease (CKD) on drug disposition has become important for the optimal design of clinical studies in patients. In this study, clinical data of 151 compounds under CKD conditions were extensively surveyed, and alterations in pharmacokinetic parameters were evaluated. In CKD patients, the unbound hepatic intrinsic clearance decreased to a similar extent for drugs eliminated via hepatic metabolism by cytochrome P450, UDP-glucuronosyltransferase, and other mechanisms. Renal clearance showed a similar decrease to glomerular filtration rate, irrespective of the contribution of tubular secretion. The scaling factor (SF) obtained from the interquartile range of the relative change in each parameter was applied to the well-stirred model to predict clearance in patients. Hepatic and renal clearance could be successfully predicted for approximately half and two-thirds, respectively, of the applied compounds, showing the high utility of SFs. SFs were also introduced to a physiologically based pharmacokinetic (PBPK) model, and the plasma concentration profiles of 12 model compounds with different elimination pathways were predicted for CKD patients. The PBPK model combined with SFs provided good predictability for plasma concentration. The developed PBPK model with information on SFs would accelerate translational research in drug development by predicting pharmacokinetics in CKD patients.

Population pharmacokinetic meta-analysis of vortioxetine in healthy individuals

The objective was to describe the pharmacokinetics of vortioxetine and evaluate the effect of intrinsic and extrinsic factors in the healthy population. Data from 26 clinical pharmacology studies were pooled. A total of 21,758 vortioxetine quantifiable plasma concentrations were collected from 887 subjects with corresponding demography. The doses ranged from 2.5 to 75 mg (single dose) and 2.5-60 mg (multiple QD doses). The pharmacokinetics of vortioxetine was best characterised by a two-compartment model with first-order absorption, lag-time and linear elimination, with interindividual error terms for absorption rate constant, oral clearance and central volume of distribution. The population mean was 32.7 L/hr for oral clearance and 1.97∙10(3)  L for the central volume of distribution. The average elimination half-life was 65.8 hr. CYP2D6 inferred metabolic status (ultra, extensive, intermediate or poor metabolisers) and age on oral clearance and height on central volume of distribution were identified as statistically significant covariate-parameter relationships. For CYP2D6 poor metabolisers, CL/F was approximately 50% to that seen in CYP2D6 extensive metabolisers. The impact of height on V2/F and age on CL/F was low and not considered to be clinically relevant. The final model was found to be reliable, stable and predictive. A reliable, stable and predictive pharmacokinetic model was developed to characterise pharmacokinetics of vortioxetine in the healthy population.

Dose selection method for pharmacokinetic study in hemodialysis patients using a subpharmacological dose: oseltamivir as a model drug

BACKGROUND

Dose selection is an important step in pharmacokinetic (PK) studies of hemodialysis patients. We propose a simulation-based dose-selection method for PK studies of hemodialysis patients using a subpharmacological dose of oseltamivir as a model drug.

METHODS

The concentrations of oseltamivir and its active metabolite, oseltamivir carboxylate (OC), were measured by liquid chromatography-tandem mass spectrometry. To determine a low oseltamivir dose exhibiting PK linearity, a pilot low dose determination investigation (n = 4) was performed using a single administration dose-escalation study. After the dose was determined, a low dose study (n = 10) was performed, and the optimal dose required to reach the hypothetical target OC exposure (area under the concentration-time curve [AUC] of 60,000 ng · hr/mL) was simulated using a nonparametric superposition method. Finally, observed PKs at the optimal dose were compared to the simulated PKs to verify PK predictability.

RESULTS

In the pilot low dose determination study, 2.5 mg of oseltamivir was determined to be the low dose. Subsequently, we performed a single-dose PK study with the low oseltamivir dose in an additional group of 10 hemodialysis patients. The predicted AUC last of OC following continuous oseltamivir doses was simulated, and 35 mg of oseltamivir corresponded to the hypothetical target AUC last of OC. The observed PK profiles of OC at a 35-mg oseltamivir dose and the simulated data based on the low dose study were in close alignment.

CONCLUSION

The results indicate that the proposed method provides a rational approach to determine the proper PK dose in hemodialysis patients.

Sources of interindividual variability

The efficacy, safety, and tolerability of drugs are dependent on numerous factors that influence their disposition. A dose that is efficacious and safe for one individual may result in sub-therapeutic or toxic blood concentrations in other individuals. A major source of this variability in drug response is drug metabolism, where differences in pre-systemic and systemic biotransformation efficiency result in variable degrees of systemic exposure (e.g., AUC, C max, and/or C min) following administration of a fixed dose.Interindividual differences in drug biotransformation have been studied extensively. It is well recognized that both intrinsic (such as genetics, age, sex, and disease states) and extrinsic (such as diet, chemical exposures from the environment, and even sunlight) factors play a significant role. For the family of cytochrome P450 enzymes, the most critical of the drug metabolizing enzymes, genetic variation can result in the complete absence or enhanced expression of a functional enzyme. In addition, up- and down-regulation of gene expression, in response to an altered cellular environment, can achieve the same range of metabolic function (phenotype), but often in a less reliably predictable and time-dependent manner. Understanding the mechanistic basis for drug disposition and response variability is essential if we are to move beyond the era of empirical, trial-and-error dose selection and into an age of personalized medicine that brings with it true improvements in health outcomes in the therapeutic treatment of disease.

A novel double-tracer technique to characterize absorption, distribution, metabolism and excretion (ADME) of [14C]tofogliflozin after oral administration and concomitant intravenous microdose administration of [13C]tofogliflozin in humans

BACKGROUND

Human mass balance studies and the assessment of absolute oral bioavailability (F) are usually assessed in separate studies. Intravenous microdose administration of an isotope tracer concomitant to an unlabeled oral dose is an emerging technique to assess F. We report a novel double-tracer approach implemented for tofogliflozin combining oral administration of a radiolabel tracer with concomitant intravenous administration of a stable isotope tracer. Tofogliflozin is a potent and selective sodium/glucose cotransporter 2 inhibitor for the treatment of type 2 diabetes mellitus currently in clinical development.

OBJECTIVES

The objectives of the present study were to assess the systemic exposure of major circulating metabolites, excretion balance, F and contribution of renal clearance (CLR) to total clearance (CL) of tofogliflozin in healthy subjects within one study applying a novel double-tracer technique.

METHODS

Six healthy male subjects received 20 mg [(12)C/(14)C]tofogliflozin (3.73 MBq) orally and a concomitant microdose of 0.1 mg [(13)C]tofogliflozin intravenously. Pharmacokinetics of tofogliflozin were determined for the oral and intravenous route; the pharmacokinetics of the metabolites M1 and M5 were determined for the oral route. Quantification of [(12)C]tofogliflozin in plasma and urine and [(13)C]tofogliflozin in plasma was performed by selective LC-MS/MS methods. For the pre-selected metabolites of tofogliflozin, M1 and M5, a validated liquid chromatography-tandem mass spectrometry (LC-MS/MS) was applied to plasma and urine samples. Total radioactivity was assessed in plasma, urine and feces. Pharmacokinetic analysis was conducted by non-compartmental methods.

RESULTS

The pharmacokinetics of tofogliflozin in healthy subjects were characterized by an F of 97.5 ± 12.3 %, CL of 10.0 ± 1.3 l/h and volume of distribution at steady-state (V(ss)) of 50.6 ± 6.7 l. The main route of elimination of total drug-related material was by excretion into urine (77.0 ± 4.1 % of the dose). The observed CL(R) of 25.7 ± 5.0 ml/min was higher than the product of the estimated glomerular filtration rate (eGFR) and fraction unbound in plasma (f(u)) (eGFR × f(u) 15 ml/min), indicating the presence of net active tubular secretion in the renal elimination of tofogliflozin. However, CLR contributed only 15.5 % to the CL of tofogliflozin, suggesting that reductions in CLR by renal impairment won't significantly affect systemic exposure to tofogliflozin. Tofogliflozin and its metabolite M1 were the only major circulating entities accounting for 46 ± 8.6 and 50 ± 8.2 %, respectively, of total circulating drug-related material, while the metabolite M5 was a minor circulating metabolite accounting for 3.0 ± 0.3 % of total circulating drug-related material. Both the M1 and M5 metabolites were excreted into urine and the major metabolite M1 did not exhibit active tubular secretion.

CONCLUSIONS

These results demonstrate the utility of the double-tracer approach to provide essential pharmacokinetic data and excretion data for drug-related material in one study at the same dosing occasion. The data obtained allowed the characterization of absorption, distribution, metabolism and excretion of tofogliflozin. Tofogliflozin exhibited highly favorable pharmacokinetic properties as demonstrated by its high F, low CL and a low V(ss. The presence of only one major circulating metabolite of tofogliflozin was unambiguously demonstrated. As a drug targeting the kidney, luminal exposure of the kidney is achieved by renal filtration and active tubular secretion.

Effect of uremic serum and uremic toxins on drug metabolism in human microsomes

There is increasing evidence that renal impairment modifies nonrenal drug clearance through drug metabolizing cytochrome P450 (CYP) enzymes. In this study, the direct inhibitory effect of serum from chronic renal failure (CRF) patients receiving dialysis was evaluated in CYP3A4 (testosterone) and CYP2B6 (bupropion) metabolism assays. Human liver microsomes were incubated with ultrafiltered serum collected pre- and post-hemodialysis from ten CRF patients. Additionally, several uremic toxins were evaluated in the CYP3A4 assay. In only three patients was there a significant decrease or increase in testosterone or bupropion metabolism post-dialysis. Urea, mannitol, guanidine, homocysteine, uridine and creatinine had no effect on CYP3A4 metabolism. CMPF, hippuric acid and p-cresol had IC50 values that fell within CRF patient plasma concentrations. The IC50 values for indoxyl sulfate and indole-3-acetic acid were greater than CRF plasma concentrations. The lack of a consistent effect on CYP3A4 or CYP2B6 metabolism by uremic serum may be due in part to the frequency of hemodialysis in these patients which reduced the accumulation of uremic toxins. CMPF, hippuric acid and p-cresol have the ability to inhibit CYP3A4 metabolism at clinical concentrations which may correspond to reports of changes in hepatic metabolism in some CRF patients.

Effects of chronic kidney disease and uremia on hepatic drug metabolism and transport

The pharmacokinetics of non-renally cleared drugs in patients with chronic kidney disease is often unpredictable. Some of this variability may be due to alterations in the expression and activity of extra-renal drug metabolizing enzymes and transporters, primarily localized in the liver and intestine. Studies conducted in rodent models of renal failure have shown decreased mRNA and protein expression of many members of the cytochrome P450 enzyme (CYP) gene family and the ATP-Binding Cassette (ABC) and Solute Carrier (SLC) gene families of drug transporters. Uremic toxins interfere with transcriptional activation, cause down-regulation of gene expression mediated by proinflammatory cytokines, and directly inhibit the activity of the cytochrome P450s and drug transporters. While much has been learned about the effects of kidney disease on non-renal drug disposition, important questions remain regarding the mechanisms of these effects, as well as the interplay between drug metabolizing enzymes and drug transporters in the uremic milieu. In this review, we have highlighted the existing gaps in our knowledge and understanding of the impact of chronic kidney disease on non-renal drug clearance, and identified areas of opportunity for future research.

The effect of hepatic or renal impairment on the pharmacokinetics of edivoxetine, a selective norepinephrine transporter reuptake inhibitor

Purpose

To assess the impact of hepatic or renal impairment on the pharmacokinetics (PK) of edivoxetine.

Methods

Two separate multi-center, open-label studies with males and females were conducted. Subjects were categorized according to their hepatic function, determined by the Child–Pugh classification, or renal function, determined by creatinine clearance using the Cockcroft–Gault equation. Subjects received a single dose of 18 mg in the hepatic impairment study or 6 mg in the renal impairment study. Noncompartmental PK parameters were computed from the edivoxetine plasma concentration–time data.

Results

In the hepatic study, the geometric least squares mean (GLSM) and 90 % confidence interval (CI) of the ratio [impaired : normal] of area under the concentration versus time curve from time zero to infinity (AUC0-∞; h × ng/mL) was 1.24 (0.93, 1.64) in the mild, 1.60 (1.21, 2.12) in the moderate, and 1.70 (1.28, 2.24) in the severe group. In the renal impairment study, the GLSM (90 % CI) of the ratio [impaired : normal] of AUC0-∞ was 1.13 (0.73, 1.73) in mild, 1.90 (1.28, 2.82) in moderate, 1.55 (0.94, 2.55) in severe, and 1.03 (0.66, 1.59) in ESRD groups. Overall, the GLSM of the ratio [impaired : normal] of C_max was slightly less than or approximately 1 across the hepatic and renal impairment groups. Across both studies, there were no clinically significant changes in vital signs and laboratory values, the adverse events were mild in severity and mostly related to nervous system and gastrointestinal disorder-related events.

Conclusions

PK changes in subjects with hepatic or renal impairment were of small magnitude and did not appear to impact overall subject tolerability. Daily dosing of edivoxetine in a larger population of impaired subjects, including those with dual impairment, would aid in establishing edivoxetine tolerability and PK in a clinical practice scenario.

Down-regulation of hepatic CYP3A and CYP2C mediated metabolism in rats with moderate chronic kidney disease

Expression and activity of drug-metabolizing enzymes are decreased in severe kidney disease; however, only a small percentage of patients with chronic kidney disease (CKD) are at the final stage of the disease. This study aimed to determine the changes in drug-metabolizing enzyme function and expression in rats with varying degrees of kidney disease. Sprague-Dawley rats were subjected to surgical procedures that allowed the generation of three distinct models of kidney function: normal kidney function, moderate kidney function, and severe kidney disease. Forty-two days after surgery, rats were sacrificed and hepatic CYP3A and CYP2C expression was determined. In addition, enzymatic activity was determined in liver microsomes by evaluating midazolam (CYP3A), testosterone (CYP3A and CYP2C), and tolbutamide (CYP2C) enzyme kinetics. Both moderate and severe kidney disease were associated with a reduction in CYP3A2 and CYP2C11 expression (p < 0.05). Likewise, moderate kidney disease resulted in more than a 60% decrease in enzyme activity (V(max)) for CYP2C11 and CYP3A, compared with controls (p < 0.05). When the degree of kidney disease was correlated with metabolic activity, an exponential decline in CYP2C- and CYP3A-mediated metabolism was observed. Our results demonstrate that CYP3A and CYP2C expression and activity are decreased in both moderate and severe CKD. Our data suggest that drug metabolism is significantly decreased in the earlier stages of CKD and imply that patients with moderate CKD may be subject to unpredictable pharmacokinetics.

Design, conduct, analysis, and interpretation of clinical studies in patients with impaired kidney function

Chronic kidney disease has been shown to alter the pharmacokinetics of drugs that are eliminated not only via the renal pathway but also by metabolism or nonrenal transport. Guidance documents from regulatory agencies on the pharmacokinetics of drugs in patients with impaired kidney function provide a framework for facilitating study design, conduct, data analysis, and the generation of dosing recommendations. Design considerations include establishment of appropriate enrollment criteria, selection of appropriate matched control group(s), and staging of impaired kidney function by estimated glomerular filtration rate or creatinine clearance. When studies in hemodialysis patients are conducted, optimizing the timing of characterization of the pharmacokinetics profile based on the schedule of hemodialysis sessions will allow for a robust assessment in these patients. In addition to traditional noncompartmental approaches, the use of pharmacometric approaches can integrate data from multiple clinical studies and provide a quantitative rationale for dose selection in patients with impaired kidney function. This article addresses the challenges and opportunities associated with the design, conduct, analysis, and interpretation of clinical studies to allow for their future facilitation and for the establishment of safe and efficacious dosing in patients with impaired kidney function.

Evaluation of exposure change of nonrenally eliminated drugs in patients with chronic kidney disease using physiologically based pharmacokinetic modeling and simulation

Chronic kidney disease, or renal impairment (RI) can increase plasma levels for drugs that are primarily renally cleared and for some drugs whose renal elimination is not a major pathway. We constructed physiologically based pharmacokinetic (PBPK) models for 3 nonrenally eliminated drugs (sildenafil, repaglinide, and telithromycin). These models integrate drug-dependent parameters derived from in vitro, in silico, and in vivo data, and system-dependent parameters that are independent of the test drugs. Plasma pharmacokinetic profiles of test drugs were simulated in subjects with severe RI and normal renal function, respectively. The simulated versus observed areas under the concentration versus time curve changes (AUCR, severe RI/normal) were comparable for sildenafil (2.2 vs 2.0) and telithromycin (1.6 vs 1.9). For repaglinide, the initial, simulated AUCR was lower than that observed (1.2 vs 3.0). The underestimation was corrected once the estimated changes in transporter activity were incorporated into the model. The simulated AUCR values were confirmed using a static, clearance concept model. The PBPK models were further used to evaluate the changes in pharmacokinetic profiles of sildenafil metabolite by RI and of telithromycin by RI and co-administration with ketoconazole. The simulations demonstrate the utility and challenges of the PBPK approach in evaluating the pharmacokinetics of nonrenally cleared drugs in subjects with RI.

Current understanding of drug disposition in kidney disease

Patients with chronic kidney disease (CKD) represent 13% of the American population. CKD has been shown to significantly alter drug disposition of nonrenally eliminated drugs. Indeed, modifications in the expression and function of intestinal and hepatic drug metabolism enzymes and uptake and efflux transporters have been reported. Uremic toxins, inflammatory cytokines, and parathyroid hormone have been implicated as causes. These changes can have an important clinical impact on drug disposition and lead to unintended toxicity if they are administered without dose adjustment in patients with impaired kidney function. This review summarizes recent preclinical and clinical studies and presents the current understanding of the effect of CKD on drug absorption, distribution, metabolism, and excretion.

A pharmacometric approach to quantify the impact of chronic kidney disease and hemodialysis on systemic drug exposure: application to saxagliptin

The draft United States Food and Drug Administration guidance recommends a dedicated pharmacokinetic (PK) study for most drugs intended for use in patients with chronic kidney disease (CKD), including stage V patients requiring hemodialysis (HD) treatment. However, clinical studies conducted in CKD patients are challenged by difficulties in recruiting stage IV and V patients not yet on dialysis, and in balancing patient characteristics among each studied CKD group. Furthermore, study design for dialysis patients often involves a single dose administered before an HD session. The design may not necessarily represent usual patient care in current clinical practice, in which multiple doses are more likely to be administered at varying times between HD sessions. Using exposure modeling of saxagliptin and its active metabolite, 5-hydroxy saxagliptin, as an example, this work illustrates how these challenges can be alleviated by modeling the impact of HD on drug exposure in clinical studies and simulating the expected exposure level in patient care. The modeled PK profiles in dialysis patients were used to understand PK profiles in patients with various CKD stages. The applied pharmacometric approach increased the efficiency of knowledge generation from existing data.

[Appropriate pharmacotherapy in patients with chronic kidney disease - new approach - ]

The kidney is the most important organ for the excretion of drugs. It was previously thought that appropriate dosages of these drugs could be easily estimated by evaluating the kidney function of patients and the excretion rate of the drug. However, the pharmacokinetic characteristics of patients with kidney disease are as follows: 1) Active metabolites with a higher polarity can accumulate, which can induce unpredictable adverse effects. For example, over sedation with morphine or the development of the fatal toxic syndrome in the case of allopulinol are due to the accumulation of active metabolites derived from these drugs. 2) Although the renal excretion rate of acetoaminophen is only less than 5%, the accumulation of its glucuronide conjugate during multiple dosing in patients with kidney failure may induce high serum acetoaminophen trough levels via the entero-hepatic circulation. 3) Although the renal excretion rate of the drugs are negligible, a remarkable increase in the serum levels of certain drugs were observed in patients with end stage kidney disease, suggesting a significant reduction in non-renal clearance probably by the accumulation of uremic toxins. For drugs that are likely to be administered to patients with kidney disease, even including drugs that are not excreted by the kidney, a full pharmacokinetic study should be conducted in patients and the results carefully assessed. Information on dosing adjustments for impaired kidney function based on estimated glomerular filtration rates should then be clearly stated in the package insert of the drugs.

A randomized, double-blind, placebo-controlled study of the safety and tolerance of regadenoson in subjects with stage 3 or 4 chronic kidney disease

BACKGROUND

The safety and tolerability of regadenoson, a pharmacologic stress agent that is excreted primarily by the kidneys, were examined in subjects with chronic kidney disease (CKD).

METHODS

This multicenter, double-blind, randomized, placebo-controlled study involved men and women, ≥18 years of age, with stage 3 or 4 [estimated glomerular filtration rate (eGFR) 30-59 mL/minute/1.73 m(2) and 15-29 mL/minute/1.73 m(2), respectively] CKD and known or suspected coronary artery disease. Subjects were randomized 2:1 to receive one 10-second intravenous injection of regadenoson 0.4 mg or placebo. The primary outcome measure was the frequency of serious adverse events over 24-h post-dose.

RESULTS

The study included 432 subjects with stage 3 (regadenoson n = 287; placebo n = 145) and 72 with stage 4 (regadenoson n = 47; placebo n = 25) CKD. No serious adverse events or deaths were reported over 24-h post-dose. The overall adverse event incidence was higher with regadenoson than placebo (62.6% vs 21.2%; P < .0001). Of the most common adverse events (≥5%) reported by subjects receiving regadenoson, headache (24.9% vs 7.1%), dyspnea (19.2% vs 0.6%), chest discomfort (14.7% vs 0.6%), nausea (14.7% vs 1.2%), flushing (12.0% vs 1.8%), and dizziness (9.6% vs 0.6%) occurred significantly more often (P < .0001) with regadenoson than placebo. There were no trends for clinically meaningful changes in eGFR from baseline to 24-h post-dose in subjects with stage 3 or 4 CKD.

CONCLUSIONS

Regadenoson was not associated with any serious or unexpected adverse events in subjects with stage 3 or 4 CKD.