The effect of different etiologies of hepatic impairment on the pharmacokinetics of gefitinib

Design and conduct considerations for studies in patients with hepatic impairment

Despite the liver being the primary site for clearance of xenobiotics utilizing a myriad of mechanisms ranging from cytochrome P450 enzyme pathways, glucuronidation, and biliary excretion, there is a dearth of information available as to how the severity of hepatic impairment (HI) can alter drug absorption and disposition (i.e., pharmacokinetics [PK]) as well as their efficacy and safety or pharmacodynamics (PD). In general, regulatory agencies recommend conducting PK studies in subjects with HI when hepatic metabolism/excretion accounts for more than 20% of drug elimination or if the drug has a narrow therapeutic range. In this tutorial, we provide an overview of the global regulatory landscape, clinical measures for hepatic function assessment, methods to stage HI severity, and consequently the impact on labeling. In addition, we provide an in-depth practical guidance for designing and conducting clinical trials for patients with HI and on the application of modeling and simulation strategies in lieu of dedicated trials for dosing recommendations in patients with HI.

The Effect of Hepatic Impairment on the Pharmacokinetics of Dacomitinib

Background and Objective

Dacomitinib is a kinase inhibitor indicated for the first-line treatment of patients with metastatic non-small cell lung cancer (NSCLC) with epidermal growth factor receptor (EGFR)-activating mutations. To evaluate the effect of hepatic impairment on the pharmacokinetics of dacomitinib, two dedicated studies were conducted to inform optimal dosing.

Methods

Study 1 (NCT01571388) evaluated the effect of mild and moderate hepatic impairment on the plasma pharmacokinetics, safety, and tolerability after a single oral dose of dacomitinib 30 mg, and Study 2 (NCT03865446) evaluated the same endpoints in a severe hepatic impairment population. Both studies were phase I, open-label, parallel-group studies. A one-way analysis of variance (ANOVA) with unequal variance assumption and hepatic impairment group as a fixed effect was used to compare the natural log of area under the plasma concentration-time curve extrapolated to infinite time (AUC_inf), AUC from time zero to the last quantifiable concentration (AUC_last), and maximum plasma concentration (C_max) for each hepatic impairment group to the respective normal hepatic function group. Since dacomitinib is a cytochrome P450 (CYP) 2D6 substrate, only participants with extensive or intermediate CYP2D6 phenotypes were included in the primary analysis.

Results

The AUC_inf for participants with mild, moderate, or severe hepatic impairment decreased by 6%, decreased by 23%, and increased by 4%, respectively, compared with normal hepatic function, while the C_max for participants with mild, moderate, or severe hepatic impairment increased by 3%, decreased by 20%, and increased by 31%, respectively, compared with normal hepatic function. A single oral dose of dacomitinib 30 mg was well tolerated in all participants.

Conclusion

Based on these pharmacokinetic results, dacomitinib pharmacokinetics of participants with mild, moderate, or severe hepatic impairment were not statistically different relative to participants with normal hepatic function based on the ANOVA analysis. No dacomitinib dose adjustments for patients with hepatic impairment are recommended.

Clinical Trial Registration

ClinicalTrials.gov NCT01571388, registered 5 April 2012; ClinicalTrials.gov NCT03865446, registered 6 March 2019.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40261-022-01125-x.

A review of the evidence base for utilizing Child-Pugh criteria for guiding dosing of anticancer drugs in patients with cancer and liver impairment

As the liver is vital for the metabolism of many anticancer drugs, determining the correct starting doses in cancer patients with liver impairment is key to safe prescription and prevention of unnecessary adverse effects. Clinicians typically use liver function tests when evaluating patients; however, prescribing information and summaries of product characteristics often suggest dosing of anticancer drugs in patients with liver impairment based on the Child-Pugh criteria, even though the criteria were not developed for this purpose. In this review, we assessed all the oncological small molecule and cytotoxic drugs approved by the United States Food and Drug Administration (FDA) over a 5-year period from 2014 to 2018. The various entry criteria related to these drugs—with respect to hepatic function—in key pivotal studies were compared with their approved dosing recommendations found in prescribing information and summaries of product characteristics. We found that 46% of drugs have dosing recommendations based on Child-Pugh criteria alone, despite the fact that only 8% of these drugs were tested within studies that used the Child-Pugh criteria as entry criteria. Moreover, we note that the data used to make recommendations based on Child-Pugh criteria are typically from small studies that may lack an appropriate patient population. We propose that these findings, along with details surrounding the development of the Child-Pugh criteria, call into question the validity and appropriateness of using Child-Pugh criteria for dosing recommendations of anticancer drugs.

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Dosing information for anticancer drugs in patients with liver impairment is often based on the Child-Pugh criteria.

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Clinical trials and clinicians typically use liver function tests when evaluating patients.

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Of the 39 oncologic drugs examined, almost half (46%) had dosing recommendations based on Child-Pugh criteria alone.

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We question whether using Child-Pugh criteria for dosing recommendations of anticancer drugs is the best approach.

Eribulin, Child-Pugh score, and liver-function tests: lessons from pivotal breast cancer studies 301 and 305

Background

The recommended starting dose of eribulin in patients with hepatic impairment is based on the Child-Pugh score, largely informed by a pharmacokinetic study of 18 patients. In the pivotal studies of eribulin in metastatic breast cancer (Study 301 and Study 305 [EMBRACE]), entry criteria and dose modifications were based on liver-function test (LFT) results rather than Child-Pugh score. In populations such as patients with metastatic breast cancer, in which metastatic infiltration is the predominant cause of hepatic impairment, using Child-Pugh score may be problematic; in clinical practice, it has been more common for oncologists to make dosing decisions based on LFTs. To address this, the effects of abnormal baseline LFT results on eribulin efficacy and safety were investigated.

Methods

In this pooled post hoc analysis, 1062 patients who were randomized to receive eribulin in Studies 301 and 305 were divided into 4 groups: (A) no elevated LFT results (no liver impairment); (B) increased levels of aspartate aminotransferase and/or alanine aminotransferase; (C) decreased albumin and/or increased levels of aspartate aminotransferase and/or alanine aminotransferase but not increased bilirubin; and (D) increased bilirubin. Patients were subcategorized by presence of liver metastasis. Drug exposure, dose intensity, and treatment-emergent adverse events (TEAEs) were analyzed.

Results

Eribulin mesylate mean dosage was 0.82 (group A)–0.65 mg/m²/week (group D). Group D had shorter treatment, more dose reductions/delays, more TEAEs leading to dose modifications, and numerically lower objective response rates and clinical benefit rates versus groups A–C. TEAE rates leading to dose modification were similar between group D (45.5%) and groups A–C (range, 43.5–54.9%) in the absence of liver metastases, but higher in group D (91.3%) compared with groups A–C (range, 41.7–54.3%) if liver metastases were present.

Conclusions

Mild elevations in bilirubin levels were associated with increased toxicity and a greater requirement for dose modifications. Based both on these study data and existing recommendations, we propose a novel scheme to guide initial dose selection in patients with metastatic breast cancer and hepatic impairment that is based on LFTs rather than Child-Pugh score.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13058-021-01407-w.

Therapeutic efficacy of lenvatinib in hepatocellular carcinoma patients with portal hypertension

AIM

Preserved liver function may be an important factor affecting therapeutic efficacy in hepatocellular carcinoma patients treated with lenvatinib, but not all patients can be treated while preserving liver function. This study evaluated the therapeutic efficacy of lenvatinib in patients with poor liver function with and without portal hypertension.

METHODS

This prospectively registered multicenter study analyzed 93 patients treated with lenvatinib. Progression-free survival was compared between patients with and without advanced portal hypertension according to baseline liver function. Advanced portal hypertension was defined as having both splenomegaly and any portosystemic collaterals.

RESULTS

A total of 37 patients (40.7%) had advanced portal hypertension. Progression-free survival did not differ between patients with and without advanced portal hypertension in the entire cohort (median 7.6 vs. 4.1 months, respectively; P = 0.148), but was significantly longer in patients with advanced portal hypertension than in those without advanced portal hypertension in the albumin-bilirubin grade 2 or 3 group (median 7.6 vs. 2.1 months, respectively; P = 0.016). In a multivariate analysis, the presence of advanced portal hypertension was identified as the only significant predictor associated with prolonged progression-free survival in the albumin-bilirubin grade 2 or 3 group.

CONCLUSIONS

Advanced portal hypertension was associated with the therapeutic efficacy of lenvatinib in controlling the progression of hepatocellular carcinoma in patients with poor liver function.

Dose recommendations for anticancer drugs in patients with renal or hepatic impairment

Renal or hepatic impairment is a common comorbidity for patients with cancer either because of the disease itself, toxicity of previous anticancer treatments, or because of other factors affecting organ function, such as increased age. Because renal and hepatic function are among the main determinants of drug exposure, the pharmacokinetic profile might be altered for patients with cancer who have renal or hepatic impairment, necessitating dose adjustments. Most anticancer drugs are dosed near their maximum tolerated dose and are characterised by a narrow therapeutic index. Consequently, selecting an adequate dose for patients who have either hepatic or renal impairment, or both, is challenging and definitive recommendations on dose adjustments are scarce. In this Review, we discuss the effect of renal and hepatic impairment on the pharmacokinetics of anticancer drugs. To guide clinicians in selecting appropriate dose adjustments, information from available drug labels and from the published literature were combined to provide a practical set of recommendations for dose adjustments of 160 anticancer drugs for patients with hepatic and renal impairment.

ABCG2 C421A polymorphisms affect exposure of the epidermal growth factor receptor inhibitor gefitinib

ATP-binding castle protein G2 (ABCG2) is thought to inhibit the activities of certain gefitinib transporters, thereby affecting drug pharmacokinetics. The C421A polymorphism affects the function and expression of ABCG2 on the cell membrane. Previous studies have shown that proton-pump inhibitors (PPIs) inhibit gefitinib absorption, as well as the function of ABCG2. We evaluated the plasma concentrations of gefitinib in patients with and without the ABCG2 C421A polymorphism, who were or were not taking PPIs. In total, 61 patients with advanced epidermal-growth-factor-positive non-small-cell lung cancer were enrolled in this study. They were treated with gefitinib at a dose of 250 mg per day. Plasma gefitinib concentration and ABCG2 C421A status were determined after 2 weeks. The patients were divided into CC- and CA/AA genotype groups. We compared the trough and peak gefitinib levels and the area under the curve (AUC) values for 24-h gefitinib concentrations. We also compared these parameters among four groups distinguished according to the presence or absence of the polymorphism and PPI use. The mean trough gefitinib level and AUC value for 24-h gefitinib concentration were significantly lower in the CA/AA group compared to the CC group (mean trough level: 333.2 vs. 454.5 ng/mL, respectively, P = 0.021; AUC: 9949.9 vs. 13,085.4 ng・h/mL, respectively, P = 0.034). Among patients taking PPIs, the mean trough gefitinib level was significantly lower in the CA/AA group than the CC group (220.1 vs. 340.5 ng/mL, respectively, P = 0.033). The CA/AA-type of ABCG2 C421A polymorphism may be associated with lower gefitinib plasma concentrations.

Updated Population Pharmacokinetic Model of Cabozantinib Integrating Various Cancer Types Including Hepatocellular Carcinoma

An integrated population pharmacokinetic (PPK) model was used to evaluate the effects of liver dysfunction on the pharmacokinetics (PK) of cabozantinib in patients with hepatocellular carcinoma and to determine whether clinical dosage adjustment may be necessary in this population. An integrated PPK model previously developed in healthy volunteers and patients with various cancer types was updated with cabozantinib concentration data from hepatocellular carcinoma patients in phase 2 and 3 studies (total 2023; hepatocellular carcinoma 489 patients). Covariate effects of cancer type including hepatocellular carcinoma population and liver dysfunction per the National Cancer Institute Organ Dysfunction Working Group criteria were evaluated (normal 1425; mild liver dysfunction 558; moderate/severe liver dysfunction 15/1 patients). With hepatocellular carcinoma patients, PK parameter estimates and covariate effects were similar to the previous PPK model (2 compartments with first‐ and zero‐order absorption and first‐order elimination). Only medullary thyroid cancer had appreciable PK differences from healthy volunteers. PK parameter estimates were similar with and without addition of liver dysfunction covariates. Patients with mild liver dysfunction were predicted to have minimal differences in apparent clearance of cabozantinib relative to patients with normal liver function. Therefore, no initial cabozantinib dosage adjustment is recommended for cancer patients with mild liver dysfunction. The small sample size for patients with moderate and severe liver dysfunction limited dosing recommendations in these subpopulations. The results from this PPK analysis were different from those of the single‐dose hepatic impairment study in healthy volunteers and more reflective of exposure in cancer patients following daily cabozantinib dosing.

Presence of pleural effusion is associated with a poor prognosis in patients with epidermal growth factor receptor-mutated lung cancer receiving tyrosine kinase inhibitors as first-line treatment

AIM

This study was conducted to evaluate the effect of clinical factors on the treatment outcomes of lung cancer patients with active epidermal growth factor receptor (EGFR) mutations treated by first-line tyrosine kinase inhibitors (TKIs).

METHODS

Patients of stage IIIb or IV lung adenocarcinoma harboring mutated EGFR were enrolled between March 2010 and June 2014 and followed up until December 2015. The effects of various clinical features, such as age, sex, smoking history, EGFR mutation types, TKIs used, presence of pleural effusion, metastatic sites on progression-free survival (PFS) and overall survival (OS), were analyzed retrospectively.

RESULTS

A total of 104 patients were included in this study. Patients with pleural effusion at initial diagnosis had significantly shorter PFS and OS than those without pleural effusion (median PFS: 8.2 months vs 15.3 months, P = 0.0004; median OS: 16.3 months vs 28.2 months, P = 0.0003). Univariate analysis revealed that being male or a smoker was associated with short PFS, whereas smoking history, bony metastasis and malignant pleural effusion were associated with poor OS. Stepwise multivariate Cox regression analysis showed that the presence of pleural effusion and different TKI use were independent prognostic factors for PFS [hazard ratio [HR] = 2.50 (95% confidence interval [CI], 1.53-4.10), P = 0.0003 and HR = 0.55 (95% CI, 0.31-0.97), P = 0.0396, respectively], whereas the presence of pleural effusion and liver metastasis were associated with poor OS [HR = 2.79 (95% CI: 1.46-5.30), P = 0.0018 and HR = 2.12 (95% CI, 1.02-4.40), P = 0.0440, respectively].

CONCLUSION

The presence of pleural effusion predicts poor PFS and OS in lung adenocarcinoma patients receiving TKIs as the first-line treatment. Additional studies are warranted to elucidate the underlying mechanisms and determine novel strategies for improving the outcome of these patients.

Safety and Pharmacokinetics of Lenvatinib in Patients with Advanced Hepatocellular Carcinoma

PURPOSE

To determine the maximum tolerable dose (MTD), safety, pharmacokinetics, pharmacodynamics, and preliminary efficacy of lenvatinib in patients with advanced hepatocellular carcinoma (HCC).

EXPERIMENTAL DESIGN

This multicenter, open-label, phase I, dose-escalation study included patients aged 20 to 80 years, refractory to standard therapy, and stratified by hepatic function measured using Child-Pugh (CP) scores: CP-A (score, 5-6) and CP-B (score, 7-8). Lenvatinib was administered continually once daily for 4-week cycles. MTD was defined as the maximum dose associated with ≤ 1 dose-limiting toxicity (DLT) occurring in cycle 1 among 6 patients.

RESULTS

In total, 20 patients (9 in CP-A and 11 in CP-B) were enrolled. The MTD was 12 and 8 mg once daily in CP-A and CP-B, respectively; DLTs included proteinuria, hepatic encephalopathy, and hyperbilirubinemia. The most common grade 3 toxicities included hypertension in CP-A and hyperbilirubinemia in CP-B. Lenvatinib plasma concentration at 24 hours after administration (C24 h) for 12 mg once daily was higher in patients with HCC than in patients with other solid tumors shown in a previous phase I study, but C24 h for 25 mg once daily lenvatinib was comparable. After lenvatinib treatment, the number of circulating endothelial and c-Kit(+) cells decreased and the levels of interleukin (IL)-6, IL10, granulocyte-colony stimulating factor, and vascular endothelial growth factor increased (P < 0.05). Partial responses were observed in 3 patients and tumor shrinkage occurred in 14 patients.

CONCLUSIONS

Lenvatinib (12 mg once daily) demonstrated preliminary efficacy with manageable toxicity and is the recommended dose for phase II studies in patients with HCC and CP-A.

Investigation of the impact of hepatic impairment on the pharmacokinetics of dacomitinib

Dacomitinib (PF-00299804) is a small-molecule inhibitor of the tyrosine kinases human epidermal growth factor receptor-1 (HER1; epidermal growth factor receptor, EGFR), HER2, and HER4 currently being developed for the treatment of lung cancer with sensitizing mutations in EGFR or refractory to EGFR-directed treatment. Dacomitinib is largely metabolized by the liver through oxidative and conjugative metabolism; therefore, determination of the impact of varying degrees of hepatic impairment on the pharmacokinetics (PK) of dacomitinib was warranted to ensure patient safety. In this phase I, open-label, parallel-group study, a single dose of dacomitinib was administered to healthy volunteers and to subjects with mild or moderate liver dysfunction, as determined by Child-Pugh classification. The primary goal of this study was to evaluate the effects of mild and moderate hepatic impairment on the single-dose PK profile of dacomitinib, as well as to assess the safety and tolerability in these subjects. Plasma protein binding and impact of hepatic function on the PK of the active metabolite PF-05199265 was also investigated. Twenty-five male subjects received dacomitinib 30 mg, with 8 subjects in the healthy- and mild-impairment cohorts and 9 subjects in the moderate-impairment cohort. Compared with healthy volunteers, there was no significant change in dacomitinib exposure in subjects with mild or moderate liver dysfunction and no observed alteration in plasma protein binding. No serious treatment-related adverse events were reported in any group, and dacomitinib was well tolerated. A dose adjustment does not appear necessary when administering dacomitinib to patients with mild or moderate hepatic impairment.

Liver metastasis predicts poorer prognosis in stage IV lung adenocarcinoma patients receiving first-line gefitinib

OBJECTIVES

Gefitinib is currently used as a first-line therapy in patients of advanced non-small cell lung cancer (NSCLC) with susceptible epidermal growth factor receptor (EGFR) mutations. However, treatment outcomes of these patients vary. This study was conducted to evaluate the impact of specific metastatic sites on treatment outcomes of patients with stage IV lung adenocarcinoma with susceptible EGFR mutations receiving first-line gefitinib, focusing on the impact of liver metastasis.

MATERIALS AND METHODS

Between October 2009 and April 2014, patients of stage IV lung adenocarcinoma harboring EGFR mutation in exon 19 or 21, who received first-line gefitinib treatment, were enrolled in two hospitals and followed until December 22, 2014. The impacts of various clinical features, including sex, age, smoking history, performance status, EGFR mutation site, metastatic sites, etc., on progression-free survival (PFS) and overall survival (OS) were analyzed.

RESULTS

A total of 148 patients were eligible for analysis. Patients with liver metastasis on initial diagnosis (n=19) had shorter PFS and OS than those without liver metastasis did (median of PFS, 6.7 vs. 11.2 months, p<0.0001; median of OS, 9.2 vs. 17.5 months, p<0.0001). Multivariable Cox regression analysis showed liver metastasis was an independent poor prognostic factor for PFS (HR=2.939 [95% CI: 1.729-4.997], p<0.0001) and OS (HR=3.300 [95% CI: 1.708-6.373], p=0.0004).

CONCLUSION

Liver metastasis predicts poorer PFS and OS in stage IV lung adenocarcinoma patients with susceptible gene mutations receiving first-line gefitinib. Further study is warranted to elucidate the underlying mechanisms and find treatment modalities to improve prognosis of these patients.

Influence of hepatic impairment on lenvatinib pharmacokinetics following single-dose oral administration

This open-label, single-dose study assessed lenvatinib pharmacokinetics (PK) in subjects with normal hepatic function (n = 8) and mild, moderate, or severe hepatic impairment (n = 6 each). Subjects received 10 mg oral lenvatinib, except those with severe hepatic impairment (5 mg). Plasma and urine samples were collected over 14 days; free and total lenvatinib and its metabolites were analyzed using validated chromatography/spectrometry. PK parameters were estimated using noncompartmental analysis. There were no clinically meaningful effects of mild or moderate hepatic impairment on lenvatinib PK. Dose-normalized Cmax for free lenvatinib was 7.0, 3.7, 5.7, and 5.6 ng/mL in subjects with normal hepatic function, mild, moderate, and severe hepatic impairment, respectively. There was no consistent trend, although dose-normalized Cmax was lower for all subjects with hepatic impairment. AUCs increased 170% and t1/2 increased (37 versus 23 hours) in subjects with severe hepatic impairment. Changes in exposure based on total plasma concentrations were generally less than those based on free concentrations, suggesting changes in plasma protein binding in subjects with severe hepatic impairment. Lenvatinib was generally well tolerated. Subjects with severe hepatic impairment should begin lenvatinib treatment at a reduced dose of 14 mg versus 24 mg for subjects with normal liver function and subjects with mild or moderate hepatic impairment.

A limited sampling strategy for estimation of the area under the plasma concentration-time curve of gefitinib

PURPOSE

The aim of this study was to develop a limited sampling strategy (LSS) to estimate the area under the concentration-time curve (AUC) of gefitinib using data from 18 patients with non-small-cell lung cancer.

METHODS

On day 14 after beginning daily therapy with 250 mg of gefitinib, plasma samples were collected just before (C(0h), 24 hours after the 13th administration) and 1, 2, 4, 6, 8, 12, and 24 hours (C(nh)) after gefitinib administration and were analyzed by high-performance liquid chromatography.

RESULTS

The predicted AUC from 0 to 24 hours (AUC₀₋₂₄) from the single time point of C(12h) showed the highest correlation with the measured AUC₀₋₂₄ of gefitinib (AUC₀₋₂₄ = 20.0 · C(12h) + 1348.0; r² = 0.9623; P , 0.0001). The 95% confidence intervals of the slopes and intercepts of the formulae obtained by bootstrap analysis indicated acceptable accuracy and robustness in the prediction of AUC₀₋₂₄ using C(0h), C(1h), C(12h), and C(1h) + C(12h). The median AUC₀₋₂₄ and C(0h) of gefitinib in patients with diarrhea (n = 8) were higher than those without diarrhea (n = 10) (15,043 versus 8918 ng·h·mL⁻¹, respectively, P = 0.0164 and 542 versus 261 ng/mL, respectively, P = 0.0263). The area under the receiver operator curve was 0.813, giving the best sensitivity (75%) and specificity (90%) at a C(0h) threshold of 398 ng/mL.

CONCLUSIONS

Use of the C(12h) single time point is recommended for the gefitinib AUC₀₋₂₄ predictive equation; however, total estimation of the AUC₀₋₂₄ of gefitinib at the single point of C(0h) was also precise. C(0h) monitoring of gefitinib might be beneficial during gefitinib therapy, because of a high variability in gefitinib exposure among patients taking 250 mg. Further examination of the correlation between clinical evaluation and the gefitinib exposure is necessary.

Pharmacokinetics of the novel PAR-1 antagonist vorapaxar in patients with hepatic impairment

PURPOSE

To determine whether hepatic impairment has an effect on the pharmacokinetics (PK) of vorapaxar or M20, its main pharmacologically active metabolite.

METHODS

This was an open-label study in which a single 40-mg oral dose of vorapaxar was administered to patients with mild (n = 6), moderate (n = 6), and severe (n = 4) hepatic impairment and healthy controls (n = 16) matched for age, gender, weight, and height. Blood samples for vorapaxar and M20 assay were collected predose and at frequent intervals up to 8 weeks postdose.

RESULTS

Plasma vorapaxar and M20 PK profiles were similar between patients with impaired liver function and healthy controls. Group mean values for vorapaxar C(max) and AUC(tf) were 206-279 ng/mL and 14,200-18,200 ng·h/mL, respectively, with the lowest values observed in patients with severe impairment. Vorapaxar median T(max) and mean t(1/2) values were 1.00-1.75 h and 298-366 h, respectively. There was no apparent correlation between vorapaxar or M20 exposure or t(1/2) values and disease severity. Vorapaxar was generally well tolerated; one serious adverse event (gastrointestinal bleeding secondary to ruptured esophageal varices) was reported in a patient with severe hepatic impairment.

CONCLUSIONS

Hepatic impairment had no clinically relevant effect on the PK of vorapaxar and M20. No dose or dosage adjustment of vorapaxar will be required in patients with mild to moderate hepatic impairment. Although systemic exposure to vorapaxar does not appear to increase in patients with severe hepatic impairment, administration of vorapaxar to such patients is not recommended given their bleeding diathesis.