No Influence of Asundexian on Cardiac Repolarization.

Inhibition of activated factor XI reduces thrombogenesis while maintaining physiological hemostasis, with the expectation of reduced bleeding risk compared with standard of care in the clinical setting. Asundexian (BAY 2433334), an activated factor XI inhibitor, is in clinical development for the prevention of thromboembolic events. The effect of asundexian and its plasma metabolite M10 on cardiac repolarization and potential interactions with the hNav1.5 sodium, hCav1.2 calcium, and human ether-à-go-go-related gene (hERG) potassium channels was investigated in vitro. Additionally, asundexian effects on cardiac parameters and electrocardiogram were examined in telemetered beagle dogs. A randomized, placebo-controlled, 4-way crossover, thorough QT study in healthy adults evaluated the influence of 50 and 150 mg of asundexian on the corrected QT interval, including 400 mg of moxifloxacin as positive control. Across all studies, asundexian and M10 were not associated with any effects on cardiac repolarization. The largest in vitro effects of asundexian (approximately 20% inhibition) were seen for hCav1.2 and hERG. Throughout the thorough QT study, the upper limits of the one-sided 95% confidence interval of placebo-corrected mean changes from baseline in Fridericia corrected QT for 50 and 150 mg of asundexian were below Δ = 10 milliseconds. Asundexian demonstrated favorable safety and tolerability profiles.

Assessment of the CYP3A4 Induction Potential by Carbamazepine: Insights from Two Clinical DDI Studies and PBPK Modeling.

In the past, rifampicin was well-established as strong index CYP3A inducer in clinical drug-drug interaction (DDI) studies. However, due to identified potentially genotoxic nitrosamine impurities, it should not any longer be used in healthy volunteer studies. Available clinical data suggest carbamazepine as an alternative to rifampicin as strong index CYP3A4 inducer in clinical DDI studies. Further, physiologically-based pharmacokinetic (PBPK) modeling is a tool with increasing importance to support the DDI risk assessment of drugs during drug development. CYP3A4 induction properties and the safety profile of carbamazepine were investigated in two open-label, fixed sequence, crossover clinical pharmacology studies in healthy volunteers using midazolam as a sensitive index CYP3A4 substrate. Carbamazepine was up-titrated from 100 mg twice daily (b.i.d.) to 200 mg b.i.d., and to a final dose of 300 mg b.i.d. for 10 consecutive days. Mean area under plasma concentration-time curve from zero to infinity (AUC(0-∞)) of midazolam consistently decreased by 71.8% (ratio: 0.282, 90% confidence interval (CI): 0.235-0.340) and 67.7% (ratio: 0.323, 90% CI: 0.256-0.407) in study 1 and study 2, respectively. The effect was adequately described by an internally developed PBPK model for carbamazepine which has been made freely available to the scientific community. Further, carbamazepine was safe and well-tolerated in the investigated dosing regimen in healthy participants. The results demonstrated that the presented design is appropriate for the use of carbamazepine as alternative inducer to rifampicin in DDI studies acknowledging its CYP3A4 inductive potency and safety profile.

Pharmacokinetics of asundexian with combined CYP3A and P-gp inhibitors and an inducer: Target in vitro and in vivo studies.

AIMS: Asundexian is an oral, direct and reversible inhibitor of activated factor XI (FXIa) in development for the treatment of thromboembolic events. This article summarizes results from preclinical and clinical studies, including identification of enzymes involved in asundexian pharmacokinetics, and evaluation of potential target drug-drug interactions. METHODS: In vitro studies investigated the substrate characteristics of asundexian towards several cytochrome P450 (CYP) isoforms, hydrolytic enzymes and drug transporters. Inhibition of the amide hydrolysis of asundexian was investigated in vitro for several relevant drugs. Phase 1 studies in healthy male participants investigated the pharmacokinetics (PK) of asundexian upon co-administration of combined inhibitors or an inducer of P-gp and CYP3A4 (itraconazole, verapamil or carbamazepine, respectively, or the moderate CYP3A4 inhibitor fluconazole). The pharmacodynamic (PD) markers are activated partial thromboplastin time and FXIa inhibition. RESULTS: Asundexian was predominantly metabolized via carboxylesterase 1 and, to a lesser extent, via CYP3A4 and is a substrate of P-gp. The asundexian area under the plasma concentration-time curve (AUC) increased by 103% and 75.6% upon combined inhibition of P-gp and strong or moderate inhibition of CYP3A4, respectively, but was unaffected by moderate CYP3A4 inhibition. Combined P-gp and CYP3A4 induction by carbamazepine decreased asundexian AUC by 44.4%. PD is concentration-dependent, thus no differences in maximum responses and recovery commensurate with PK effect(s) were observed. Adverse events were mild and asundexian was well tolerated. CONCLUSIONS: The presented studies confirmed that CYP3A4 and P-gp contribute to asundexian metabolism and excretion. Observed effects were in line with data from a previous mass balance study.

Metabolism and Disposition of the Novel Oral Factor XIa Inhibitor Asundexian in Rats and in Humans.

BACKGROUND AND OBJECTIVES: Current anticoagulants pose an increased risk of bleeding. The development of drugs targeting factor XIa, like asundexian, may provide a safer treatment option. A human mass­balance study was conducted to gain a deeper understanding of the absorption, distribution, metabolism, excretion, and potential for drug-drug interaction of asundexian. Additionally, an overview of the biotransformation and clearance pathways for asundexian in humans and bile-duct cannulated (BDC) rats in vivo, as well as in vitro in hepatocytes of both species, is reported. METHODS: The mass balance, biotransformation, and excretion pathways of asundexian were investigated in six healthy volunteers (single oral dose of 25 mg [14C]asundexian) and in BDC rats (intravenous [14C]asundexian 1 mg/kg). RESULTS: Overall recovery of radioactivity was 101% for humans (samples collected up to 14 days after dosing), and 97.9% for BDC rats (samples collected in the 24 h after dosing). Radioactivity was mainly excreted into feces in humans (80.3%) and into bile/feces in BDC rats (> 94%). The predominant clearance pathways in humans were amide hydrolysis to metabolite M1 (47%) and non-labeled M9 with subsequent N-acetylation to M10; oxidative biotransformation was a minor pathway (13%). In rats, hydrolysis of the terminal amide to M2 was the predominant pathway. In human plasma, asundexian accounted for 61.0% of total drug-related area under the plasma concentration-time curve (AUC); M10 was the major metabolite (16.4% of the total drug-related AUC). Excretion of unmetabolized drug was a significant clearance pathway in both species (human, ~ 37%; BDC rat, ~ 24%). The near-complete bioavailability of asundexian suggests negligible limitations on absorption and first-pass metabolism. Comparison with radiochromatograms from incubations with human or rat hepatocytes indicated consistency across species and a good overall in vitro/in vivo correlation. CONCLUSIONS: Similar to preclinical experiments, total asundexian-derived radioactivity is cleared quantitatively predominantly via feces. Excretion occurs mainly via amide hydrolysis and as the unchanged drug.

Effects of Tablet Formulation, Food, or Gastric pH on the Bioavailability of Asundexian.

Absolute bioavailability (F) and the impact of gastric pH, tablet formulation, and food on the pharmacokinetics and safety of asundexian, an oral factor XIa inhibitor, was assessed in healthy White men aged 18-45 years in 4 studies. For F, fasted participants received 50 µg of [13 C7 ,15 N]-labeled asundexian intravenously 2 hours after 25 mg of asundexian orally. Tablet formulation (50-mg immediate release [IR], and different amorphous solid dispersion [ASD] IR 25-mg and 50-mg ASD IR tablets) and food effects were explored in 2 studies. Formulation was compared using 50-mg IR versus 25-mg ASD IR and 25-mg ASD IR versus 50-mg ASD IR (fasted); food effect using 25-mg ASD IR and 50-mg ASD IR. Gastric pH modulation was assessed using omeprazole or antacid coadministration with asundexian in the fasted state. Pharmacokinetic parameters included area under the concentration-time curve (AUC; and AUC/dose [D]) and maximum observed concentration (Cmax and Cmax /D) data were evaluable for 59 participants. F was 103.9%. Relative bioavailability with 25-mg ASD IR and 50-mg ASD IR tablets, respectively, was marginally affected by formulation (AUC/D ratios, 94.3% and 95.1%; Cmax /D ratios, 95.5% and 88.7%), food (AUC[/D] ratios, 91.1% and 96.9%; Cmax [/D] ratios: 78.3% and 95.1%), and gastric pH (omeprazole, no effect; antacid, AUC ratio, 89.9% and Cmax ratio, 83.7%). No serious adverse events or deaths occurred; most adverse events were mild or moderate. In summary, oral asundexian was well tolerated and demonstrated complete bioavailability irrespective of tablet formulation, food, or gastric pH.

Pharmacokinetics, pharmacodynamics and safety of BAY 2433334, a novel activated factor XI inhibitor, in healthy volunteers: A randomized phase 1 multiple-dose study.

AIM: To evaluate BAY 2433334, an oral activated factor XI (FXIa) inhibitor, in volunteers. METHODS: Phase 1 study of healthy men at a German centre. Part A: randomized, single-blind, multiple dose-escalation study of BAY 2433334 (25/50/100 mg once daily [OD]) vs. placebo. Part B: similar design to Part A; evaluated BAY 2433334 25 mg twice daily. Part C: nonrandomized, open-label study; evaluated potential interactions between BAY 2433334 (25/75 mg OD) and midazolam (7.5 mg), a CYP3A4 index substrate. Primary variables: treatment-emergent adverse events (TEAEs; Parts A and B); area under the plasma concentration-time curve (AUC) and maximum plasma concentration of midazolam and α-hydroxymidazolam (Part C). STUDY PERIOD: 18 days plus follow-up visit. RESULTS: Parts A and B: 36 participants randomized to BAY 2433334; 12 to placebo. Part C: 48 participants assigned to BAY 2433334 plus midazolam. BAY 2433334 was well tolerated in all study parts. AUC and maximum plasma concentration of BAY 2433334 in plasma appeared dose proportional over 25-100 mg OD, with low-to-moderate variability in pharmacokinetic parameters. Multiple dosing caused minor-to-moderate accumulation and a mean terminal half-life (15.8-17.8 h) supporting once-daily dosing. Dose-dependent FXIa activity inhibition and activated partial thromboplastin time prolongation were observed. BAY 2433334 appeared to have a minor effect on AUC for midazolam (ratio [90% confidence interval]: 1.1736 [1.0963-1.2564]) and α-hydroxymidazolam (0.9864 [0.9169-1.0612]) only for BAY 2433334 75 mg OD on day 10. CONCLUSION: Multiple dosing of BAY 2433334 in healthy volunteers was well tolerated, with a predictable pharmacokinetic/pharmacodynamic profile and no clinically relevant CYP3A4 induction or inhibition.

First evaluation of the safety, pharmacokinetics, and pharmacodynamics of BAY 2433334, a small molecule targeting coagulation factor XIa.

BACKGROUND: Coagulation factor XI (FXI) contributes to the development of thrombosis but appears to play a minor role in hemostasis and is, therefore, an attractive anticoagulant drug target. OBJECTIVES: To evaluate the safety, pharmacokinetic, and pharmacodynamic properties of BAY 2433334, an orally administered small molecule targeting activated FXI (FXIa), in healthy men. PATIENTS/METHODS: This phase 1 study was conducted in two parts. In part 1, 70 volunteers were randomized 4:1 to receive a single oral dose of BAY 2433334 (5-150 mg as oral solution or immediate-release tablets) or placebo. In part 2, 16 volunteers received a single oral dose of five BAY 2433334 5-mg tablets with or without a high-calorie breakfast in a randomized crossover study design. Adverse events, pharmacokinetic parameters, and pharmacodynamic parameters were assessed up to 72 h after drug administration. Volunteers were followed up after 7 to 14 days. RESULTS: BAY 2433334 demonstrated favorable safety and tolerability with a dose-dependent increase in exposure and a terminal half-life of 14.2 to 17.4 h. A high-calorie breakfast reduced mean maximum plasma concentration and exposure by 31% and 12.4%, respectively. AY 2433334 was associated with a dose-dependent inhibition of FXIa activity and an increase in activated partial thromboplastin time. Bleeding times in volunteers who had received BAY 2433334 were similar to those in volunteers who had received placebo. CONCLUSIONS: These data indicate that BAY 2433334 is a promising development candidate for once-daily oral anticoagulation; it is being evaluated in phase 2 dose-finding studies in patients at risk of thrombosis.

Effects of the chymase inhibitor fulacimstat in diabetic kidney disease-results from the CADA DIA trial.

BACKGROUND: The protease chymase generates multiple factors involved in tissue remodelling including angiotensin II (Ang II) and has been implicated in the pathophysiology of diabetic kidney disease (DKD). This study investigated the effects of the chymase inhibitor fulacimstat on albuminuria in patients with Type II diabetes mellitus and a clinical diagnosis of DKD. METHODS: In this double-blind, randomized, placebo-controlled trial, patients were on the maximum tolerated dose of either an Ang II receptor blocker or an Ang-converting enzyme inhibitor since at least 3 months before the screening visit. Eligible patients were randomized in a 2:1 ratio to treatment with either 25 mg fulacimstat (n = 99) or placebo (n = 48) twice daily on top of standard of care. RESULTS: The randomized patients had a mean urine albumin-creatinine ratio (UACR) of 131 mg/g (range: 29-2429 mg) and a mean (standard deviation) estimated glomerular filtration rate of 60.8 ± 16.9 mL/min/1.73 m2 before treatment start. Fulacimstat was safe and well tolerated, and achieved mean total trough concentrations that were ∼9-fold higher than those predicted to be required for minimal therapeutic activity. UACR increased by 27.4% [coefficient of variation (CV) 86%] and 3% (CV 88.9%) after 24 weeks of treatment with placebo or fulacimstat, respectively. Analysis of covariance revealed a least square mean UACR ratio (fulacimstat/placebo) of 0.804 (90% CI 0.627-1.030, P = 0.1477), indicating a statistically non-significant UACR reduction of 19.6% after fulacimstat treatment compared with placebo. CONCLUSIONS: Fulacimstat was safe and well tolerated but did not reduce albuminuria in patients with DKD. These findings do not support a therapeutic role for chymase inhibition in DKD.

Effects of the chymase inhibitor fulacimstat on adverse cardiac remodeling after acute myocardial infarction-Results of the Chymase Inhibitor in Adverse Remodeling after Myocardial Infarction (CHIARA MIA) 2 trial.

BACKGROUND: Adverse cardiac remodeling is a major risk factor for the development of post myocardial infarction (MI) heart failure (HF). This study investigates the effects of the chymase inhibitor fulacimstat on adverse cardiac remodeling after acute ST-segment-elevation myocardial infarction (STEMI). METHODS: In this double-blind, randomized, placebo-controlled trial patients with first STEMI were eligible. To preferentially enrich patients at high risk of adverse remodeling, main inclusion criteria were a left-ventricular ejection fraction (LVEF) ≤45% and an infarct size >10% on day 5 to 9 post MI as measured by cardiac MRI. Patients were then randomized to 6 months treatment with either 25 mg fulacimstat (n = 54) or placebo (n = 53) twice daily on top of standard of care starting day 6 to 12 post MI. The changes in LVEF, LV end-diastolic volume index (LVEDVI), and LV end-systolic volume index (LVESVI) from baseline to 6 months were analyzed by a central blinded cardiac MRI core laboratory. RESULTS: Fulacimstat was safe and well tolerated and achieved mean total trough concentrations that were approximately tenfold higher than those predicted to be required for minimal therapeutic activity. Comparable changes in LVEF (fulacimstat: 3.5% ±â€¯5.4%, placebo: 4.0% ±â€¯5.0%, P = .69), LVEDVI (fulacimstat: 7.3 ±â€¯13.3 mL/m2, placebo: 5.1 ±â€¯18.9 mL/m2, P = .54), and LVESVI (fulacimstat: 2.3 ±â€¯11.2 mL/m2, placebo: 0.6 ±â€¯14.8 mL/m2, P = .56) were observed in both treatment arms. CONCLUSION: Fulacimstat was safe and well tolerated in patients with left-ventricular dysfunction (LVD) after first STEMI but had no effect on cardiac remodeling.

Safety and Tolerability of the Chymase Inhibitor Fulacimstat in Patients With Left Ventricular Dysfunction After Myocardial Infarction-Results of the CHIARA MIA 1 Trial.

The chymase inhibitor fulacimstat is developed as a first-in-class treatment option for the inhibition of adverse cardiac remodeling in patients with left ventricular dysfunction (LVD) after acute myocardial infarction (MI). The aim of the study was to examine the safety and tolerability of fulacimstat in patients with LVD after remote MI. A multicenter, multinational randomized, placebo-controlled study was performed in clinically stable patients (40-79 years of age, left ventricular ejection fraction ≤ 45% because of MI in medical history) who were on stable evidence-based standard-of-care therapies for LVD post-MI including an angiotensin converting enzyme inhibitor or angiotensin receptor blocker at doses of at least half the recommended target dose. Patients were treated for 2 weeks with either placebo (n = 12) or 4 different doses of fulacimstat (5 mg twice daily, n = 9; 10 mg twice daily, n = 9; 25 mg twice daily, n = 10; 50 mg once daily, n = 9). Fulacimstat was safe and well tolerated at all examined doses. There were no clinically relevant effects on vital signs or potassium levels compared with placebo treatment. Mean plasma concentrations of fulacimstat increased with the administered dose and reached exposures predicted to be therapeutically active. The safety profile and the absence of effects on blood pressure or heart rate in a chronic patient population having similar comorbidities and receiving similar comedication as patients after acute MI support future clinical trials with fulacimstat in patients after acute MI.

Pharmacokinetics, Safety, and Tolerability of the Novel Chymase Inhibitor BAY 1142524 in Healthy Male Volunteers.

The orally available chymase inhibitor BAY 1142524 is currently being developed as a first-in-class treatment for left-ventricular dysfunction after myocardial infarction. Results from 3 randomized, single-center, phase 1 studies in healthy male volunteers examining the safety, tolerability, and pharmacokinetics of BAY 1142524 are summarized. In this first-in-human study, single oral doses of 1-200 mg were administered in fasted state as liquid service formulation or immediate release (IR) tablets. The relative bioavailability and the effect of a high-fat/high-calorie meal were investigated at the 5-mg dose. In a multiple-dose escalation study, doses of 5-50 mg twice daily and 100 mg once daily were given for 5 consecutive days. BAY 1142524 was safe and well tolerated and had no effects on heart rate or blood pressure compared with placebo. BAY 1142524 was absorbed with peak concentration 1-3 hours after administration for IR tablets; it was eliminated from plasma with a terminal half-life of 6.84-12.0 hours after administration of liquid service formulation or IR tablets. Plasma exposures appeared to be dose-linear, with a negligible food effect. There was only low accumulation of BAY 1142524 after multiple dosing. BAY 1142524 exhibited a pharmacokinetic profile allowing for once-daily dosing. The absence of blood pressure effects after administration of BAY 1142524 supports the combination of this novel anti-remodeling drug with existing standard of care in patients with left-ventricular dysfunction after acute myocardial infarction.

FOLFIRI and sunitinib as first-line treatment in metastatic colorectal cancer patients with liver metastases--a CESAR phase II study including pharmacokinetic, biomarker, and imaging data.

BACKGROUND: The aim of this study was the evaluation of pharmacokinetic parameters, biomarkers, clinical outcome, and imaging parameters in metastatic colorectal cancer (mCRC) patients treated with FOLFIRI plus sunitinib. METHODS: mCRC patients with liver metastases were treated with FOLFIRI and sunitinib as 1st line therapy. At protocol-defined time points, multicontrast magnetic resonance imaging (MRI)measurements, computed tomography (CT) scans, pharmacokinetics (PK), and biomarker analyses were performed during the first and second treatment cycle. Thereafter, patients were treated until tumor progression, investigator’s decision due to toxicity, or patient withdrawal. RESULTS: 28 patients were screened, 26 were included, and 23 received at least one study medication. Full safety analysis was performed in 23 patients. Full PK and biomarker analyses were performed in 21 patients. Strong responses in tumor size reduction forced a change from the original imaging timing scheme. This unforeseen change in the timing scheme resulted in subgroups too small for meaningful statistical analysis of most imaging parameters. Thus, only a descriptive analysis of the MRI data was possible. In 21/22 patients, MRI showeda decrease of the liver metastases. Best response was partial remission (PR) in 8/17 patients. Plasma concentrations of sVEGFR-2 and sVEGFR-3 decreased in all patients. The majority of the patients developed some kind of toxicity not always deducible to FOLFIRI or sunitinib. CONCLUSIONS: Due to the observed side effect profile, FOLFIRI plus sunitinib 37.5 mg per day cannot be recommended for previously untreated mCRC.

Determination of soluble vascular endothelial growth factor receptor 3 (sVEGFR-3) in plasma as pharmacodynamic biomarker.

Soluble VEGFR-3 (sVEGFR-3) is a potential biomarker for the anti-angiogenic activity of tyrosine kinase inhibitors. The aim of this investigation was the validation of an enzyme-linked immunosorbent assay (ELISA) to measure sVEGFR-3 in human plasma and the investigation of its applicability in clinical trials as first step of the biomarker validation process. General validation criteria were assessed based on current guidelines and recommendations for immunoassays. The ELISA was applied in two clinical trials including healthy volunteers and metastatic colorectal cancer (mCRC) patients receiving 50 or 37.5mg sunitinib per day, respectively. SVEGFR-3 was measured at predefined time points. Undiluted, inactivated fetal calf serum was identified as surrogate matrix to substitute for human plasma. Dilutional linearity and parallelism could be successfully confirmed. The analyte was measured in the study matrix with intra- and inter-run precision and accuracy ≤20%. Stability was proven over a period of at least 15 months as well as upon three freeze-thaw cycles. SVEGFR-3 concentrations decreased in response to sunitinib to 57% (IQR 50-88%) and 58% (IQR 47-80%) of the respective baseline concentrations in healthy volunteers and mCRC patients, respectively, with subsequent increase after stop of treatment. The ELISA for the quantification of sVEGFR-3 in human plasma was successfully validated. The applicability of the assay was demonstrated in two clinical trials.

Clinical pharmacokinetics of tyrosine kinase inhibitors: focus on pyrimidines, pyridines and pyrroles.

Pyrimidine (imatinib, dasatinib, nilotinib and pazopanib), pyridine (sorafenib) and pyrrole (sunitinib) tyrosine kinase inhibitors (TKIs) are multi-targeted TKIs with high activity towards several families of receptor and non-receptor tyrosine kinases involved in angiogenesis, tumour growth and metastatic progression of cancer. These orally administered TKIs have quite diverse characteristics with regard to absorption from the gastrointestinal tract. Absolute bioavailability in humans has been investigated only for imatinib (almost 100%) and pazopanib (14-39%; n = 3). On the basis of human radioactivity data, dasatinib is considered to be well absorbed after oral administration (19% and 0.1% of the total radioactivity were excreted as unchanged dasatinib in the faeces and urine, respectively). Quite low absolute bioavailability under fasted conditions is assumed for nilotinib (31%), sorafenib (50%) and sunitinib (50%). Imatinib, dasatinib and sunitinib exhibit dose-proportional increases in their area under the plasma concentration-time curve values over their therapeutic dose ranges. Less than dose-proportional increases were observed for nilotinib at doses ≥400 mg/day and for sorafenib and pazopanib at doses ≥800 mg/day. At steady state, the accumulation ratios are 1.5-2.5 (unchanged imatinib), 2.0 (nilotinib once-daily dosing), 3.4 (nilotinib twice-daily dosing), 1.2-4.5 (pazopanib), 5.7-6.4 (sorafenib) and 3.0-4.5 (sunitinib). Concomitant intake of a high-fat meal does not alter exposure to imatinib, dasatinib and sunitinib but leads to considerably increased bioavailability of nilotinib and pazopanib and decreased bioavailability of sorafenib. With the exception of pazopanib, the TKIs described here have large apparent volumes of distribution, exceeding the volume of body water by at least 4-fold. Very low penetration into the central nervous system in humans has been reported for imatinib and dasatinib, but there are currently no published human data for nilotinib, pazopanib, sorafenib or sunitinib. All TKIs that have been described are more than 90% bound to the plasma proteins: α(1)-acid glycoprotein and/or albumin. They are metabolized primarily via cytochrome P450 (CYP) 3A4, the only exception being sorafenib, for which uridine diphosphate glucuronosyltransferase 1A9 is the other main enzyme involved. Active metabolites of imatinib and sunitinib contribute to their antitumour activity. Although some patient demographics have been identified as significant co-factors that partly explain interindividual variability in exposure to TKIs, these findings have not been regarded as sufficient to recommend age-, sex-, bodyweight- or ethnicity-specific dose adjustment. Systemic exposure to imatinib, sorafenib and pazopanib increases in patients with hepatic impairment, and reduction of the initial therapeutic dose is recommended in this subpopulation. The starting dose of imatinib should also be reduced in renally impaired subjects. Because the solubility of dasatinib is pH dependent, co-administration of histamine H(2)-receptor antagonists and proton pump inhibitors with dasatinib should be avoided. With the exception of sorafenib, systemic exposure to TKIs is significantly decreased/increased by co-administration of potent CYP3A4 inducers/inhibitors, and so it is strongly recommended that the TKI dose is adjusted or that such co-administration is avoided. Caution is also recommended for co-administration of CYP3A4 substrates with TKIs, especially for those with a narrow therapeutic index. However, current recommendations with regard to dose adjustment of TKIs need to be validated in clinical studies. Further investigations are needed to explain the large interindividual variability in the pharmacokinetics of these drugs and to assess theclinical relevance of their interaction potential and inhibitory effects on metabolizing enzymes and transporters.