Mass balance study of [¹⁴C]eribulin in patients with advanced solid tumors

Human absorption, distribution, metabolism, and excretion studies: Conventional or microtracer?

A human absorption, distribution, metabolism, and excretion (hADME) study is an essential clinical pharmacology study for small-molecule drugs. The study provides insights into circulating drug-related materials and the drug's elimination pathways in humans, which can guide future studies on safety and drug-drug interaction of metabolites as well as organ impairment and drug-drug interaction of the parent drug. The 2 hADME study types, namely conventional and microtracer, are comprehensively compared in this manuscript. A review of literature found that conventional hADME studies were approximately 7 times that of microtracer hADME studies for small molecule and peptide drugs based on publications in 3 peer-reviewed journals from 2010 to 2024. Each study type has advantages and disadvantages. The advantages of conventional hADME studies primarily include the ease, low cost, and flexibility of radiometric sample analysis. In contrast, the advantages of microtracer hADME studies primarily include exemption from prerequisite studies and use of non-good manufacturing practice 14C-labeled materials. The disadvantages of each study type are essentially the advantages of the other. The manuscript also discusses scenarios where a microtracer hADME study may be preferable. Finally, recommendations are provided on selecting the appropriate hADME study type for an investigational drug. SIGNIFICANCE STATEMENT: The manuscript discusses 2 primary human absorption, distribution, metabolism, and excretion study types: conventional and microtracer. It covers published literature studies, the pros and cons of each type, scenarios for conducting microtracer studies, and a recommended decision tree for selecting the appropriate human absorption, distribution, metabolism, and excretion study type.

Acute-on-chronic liver failure following eribulin treatment for metastatic breast cancer: a case report

The efficacy and tolerability of eribulin mesylate, a synthetic halichondrin B analog, in patients with metastatic breast cancer (MBC) previously treated with anthracyclines and taxanes have been established. Acute-on-chronic liver failure (ACLF) is a clinical syndrome manifesting as acute and severe hepatic derangement resulting from varied insults in patients with established chronic liver disease or cirrhosis who did not previously receive eribulin. A middle-aged woman diagnosed with MBC and diffuse liver metastases who was pretreated with multi-line chemotherapy received eribulin as eighth-line chemotherapy and presented with hepatic encephalopathy, rapid bilirubin elevation, and significant coagulation dysfunction on day 4 in cycle 1. The patient was diagnosed with ACLF induced by eribulin. Therefore, ACLF may be a lethal and rare adverse event when patients with chronic liver metastases receive eribulin treatment, and clinicians' awareness should be increased for optimal prevention and prompt diagnosis and treatment.

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.

Review of Chromatographic Bioanalytical Assays for the Quantitative Determination of Marine-Derived Drugs for Cancer Treatment

The discovery of marine-derived compounds for the treatment of cancer has seen a vast increase over the last few decades. Bioanalytical assays are pivotal for the quantification of drug levels in various matrices to construct pharmacokinetic profiles and to link drug concentrations to clinical outcomes. This review outlines the different analytical methods that have been described for marine-derived drugs in cancer treatment hitherto. It focuses on the major parts of the bioanalytical technology, including sample type, sample pre-treatment, separation, detection, and quantification.

Clinical efficacy of eribulin mesylate for the treatment of metastatic soft tissue sarcoma

INTRODUCTION

Metastatic soft tissue sarcoma, a devastating disease, has a median overall survival of only 12-18 months. Treatment options remain scarce. However, eribulin mesylate, a first-in-class halichondrin B-based microtubule dynamics inhibitor, has recently been approved for the management of patients with advanced liposarcoma. Areas covered: Based on a review of the literature between 2005 and 2017, we present a summary of eribulin mesylate's mechanism of action and the studies showing its clinical efficacy in locally advanced or metastatic sarcomas. Expert commentary: Future development includes the definition of a biomarker signature related to patient outcome with eribulin. Further investigation via controlled clinical trials is needed to identify combination regimens that can optimize the efficacy of eribulin while providing an acceptable safety profile in sarcoma patients.

Phase I dose-finding study of eribulin and capecitabine for metastatic breast cancer: JBCRG-18 cape study

Background

Eribulin is a nontaxane microtubule inhibitor with activity in patients with metastatic breast cancer (MBC). We conducted a phase I dose-finding study of eribulin and capecitabine in patients with MBC pretreated with anthracycline and taxane.

Methods

Women with MBC aged ≤70 years were enrolled. A 3 + 3 dose escalation design was used: level 0 dosing, eribulin (1.4 mg/m² intravenously on days 1 and 8) plus capecitabine [825 mg/m² orally twice daily (BID)]; 2-weeks-on, 1-week-off in a 21-day cycle. If there were no dose-limiting toxicities (DLTs), level 1 capecitabine dose was 1000 mg/m² BID. The primary objective was to determine maximum tolerated dose, DLTs, and recommended dose (RD). Secondary objectives included pharmacokinetics, safety, and best overall response rate.

Results

Nine women with MBC were enrolled; six at level 0, three at level 1. One patient had grade 4 DLTs at level 0 (serum creatinine 7.65 mg/dL and uric acid 13.4 mg/dL), considered associated with study drugs. Level 1 dosing was taken as the RD. Neutropenia was the most common ≥grade 3 toxicity. Pharmacokinetic parameters of eribulin were not influenced by co-administration of capecitabine. Of three patients in level 1, one achieved partial response and one had prolonged stable disease.

Conclusion

Eribulin with capecitabine in the level 1 dosing schedule was associated with manageable toxicities and promising clinical activity. This combination is recommended for phase II investigation.

Electronic supplementary material

The online version of this article (doi:10.1007/s12282-017-0798-4) contains supplementary material, which is available to authorized users.

Eribulin shows high concentration and long retention in xenograft tumor tissues

Purpose

Eribulin, a synthetic analog of the natural product halichondrin B, is a microtubule dynamics inhibitor. In this study, we report the pharmacokinetic profiles of eribulin in mice, rats, and dogs following intravenous administrations with optimized and validated bio-analytical methods.

Methods

Eribulin was administered at 0.5 and 2 mg/kg in mice, 0.5 and 1 mg/kg in rats, and 0.08 mg/kg in dogs. Tumor and brain penetration of eribulin was also evaluated in LOX human melanoma xenograft models. Concentrations in plasma, tumor, and brain were measured by the LC–MS/MS method.

Results

The profiles of eribulin were characterized by extensive distribution, moderate clearance, and slow elimination in the three species. The pharmacokinetics are linear in mice and rats. In xenograft mice, the penetration into the brain was low, as expected, since eribulin is a P-glycoprotein substrate. In contrast to disposition in brain, the exposure of eribulin was approximately 20–30 times higher in tumor than that in plasma and half-lives were 17.8–35.9 h after both single and multiple dose regimens.

Conclusions

Eribulin was distributed rapidly and eliminated slowly in mice, rats, and dogs. The exposure of eribulin was approximately 20–30 times higher in tumor than in plasma in xenograft mice. These results might be caused by eribulin’s mechanism of action including increased perfusion in tumor by vascular remodeling effect.

Integrating mechanisms of response and resistance against the tubulin binding agent Eribulin in preclinical models of osteosarcoma

Osteosarcoma is the most frequently occurring bone cancer in children and adolescents. Unfortunately, treatment failures are common. Eribulin is a synthetic microtubule inhibitor that has demonstrated activity in preclinical osteosarcoma models. The effects of eribulin were evaluated in two human osteosarcoma cell lines as well as in eribulin-sensitive and -resistant osteosarcoma xenograft tumors of the Pediatric Preclinical Testing Program (PPTP) by characterizing cell viability, microtubule destabilization, mitotic arrest and mechanism of cell death. Eribulin demonstrated cytotoxic activity in vitro, through promotion of microtubule dynamic instability, arrest of cells in the G2/M phase, mitotic catastrophe and cell death. The microtubule-destabilizing protein stathmin-1 (STMN1) was coimmunoprecipitated with the cyclin-dependent kinase inhibitor p27 indicating that these cytoplasmic complexes can protect cells from the microtubule destabilizing effect of eribulin. Increased tumoral expression of P-glycoprotein (P-gp) and TUBB3 were also associated with lower drug sensitivity. In summary, eribulin successfully blocked cells in G2/M phase but interfered with mitochondria activity to inhibit proteins involved in apoptosis. Understanding the complex and inter-related mechanisms involved in the overall drug response to eribulin may help in the design of therapeutic strategies that enhance drug activity and improve benefits of eribulin in pediatric patients with osteosarcoma.

Regulatory aspects of human radiolabeled mass balance studies in oncology: concise review

Human radiolabeled mass balance studies are performed to obtain information about the absorption, distribution, metabolism, and excretion of a drug in development. The main goals are to determine the route of elimination and major metabolic pathways. This review provides an overview of the current regulatory guidelines concerning human radiolabeled mass balance studies and discusses scientific trends seen in the last decade with a focus on mass balance studies of anticancer drugs. This paper also provides an overview of mass balance studies of anticancer agents that were executed in the last 10 years.

Pharmacokinetics of Selected Anticancer Drugs in Elderly Cancer Patients: Focus on Breast Cancer

Background: Elderly patients receiving anticancer drugs may have an increased risk to develop treatment-related toxicities compared to their younger peers. However, a potential pharmacokinetic (PK) basis for this increased risk has not consistently been established yet. Therefore, the objective of this study was to systematically review the influence of age on the PK of anticancer agents frequently administered to elderly breast cancer patients. Methods: A literature search was performed using the PubMed electronic database, Summary of Product Characteristics (SmPC) and available drug approval reviews, as published by EMA and FDA. Publications that describe age-related PK profiles of selected anticancer drugs against breast cancer, excluding endocrine compounds, were selected and included. Results: This review presents an overview of the available data that describe the influence of increasing age on the PK of selected anticancer drugs used for the treatment of breast cancer. Conclusions: Selected published data revealed differences in the effect and magnitude of increasing age on the PK of several anticancer drugs. There may be clinically-relevant, age-related PK differences for anthracyclines and platina agents. In the majority of cases, age is not a good surrogate marker for anticancer drug PK, and the physiological state of the individual patient may better be approached by looking at organ function, Charlson Comorbidity Score or geriatric functional assessment.

Pharmacokinetics of eribulin mesylate in cancer patients with normal and impaired renal function

Purpose

To evaluate the effect of renal impairment on eribulin mesylate pharmacokinetics following a single dose in adults with advanced solid tumors.

Methods

Patients were grouped by renal function: moderate impairment (creatinine clearance [CrCl] 30–50 mL/min), severe impairment (CrCl 15–29 mL/min), or normal (CrCl ≥80 mL/min). During each 21-day cycle, eribulin mesylate doses (days 1 and 8) were administered intravenously: moderate, 1.1 mg/m² (except cycle 1 day 1, 1.4 mg/m²); severe, 0.7 mg/m²; normal, 1.4 mg/m².

Results

Nineteen patients were enrolled (normal, n = 6; moderate, n = 7; severe, n = 6). Renal impairment was associated with an increased mean dose-normalized area under the concentration–time curve (ratios for moderate/normal and severe/normal: 1.49; 90 % confidence interval [CI] 0.9, 2.45). CrCl and renal function correlated positively, with a numerically small slope (0.0184; 90 % CI −0.00254, 0.0394). A simulated dose reduction to eribulin 1.1 mg/m² in patients with moderate or severe renal impairment achieved the same exposure as 1.4 mg/m² in those with normal renal function. All groups had similar toxicity profiles, with no unexpected adverse events.

Conclusions

Renal impairment decreased eribulin clearance and increased exposure. Pharmacokinetic evaluation supports an eribulin dose reduction to 1.1 mg/m² in patients with moderate or severe renal impairment.

ClinicalTrials.gov Identifier

NCT01418677.

Eribulin in Cancer Treatment

Halichondrin B is a complex, natural, polyether macrolide derived from marine sponges. Eribulin is a structurally-simplified, synthetic, macrocyclic ketone analogue of Halichondrin B. Eribulin was approved by United States Food and Drug Administration in 2010 as a third-line therapy for metastatic breast cancer patients who have previously been treated with an anthracycline and a taxane. It has a unique microtubule dynamics inhibitory action. Phase III studies have either been completed or are currently ongoing in breast cancer, soft tissue sarcoma, and non-small cell lung cancer. Phase I and II studies in multiple cancers and various combinations are currently ongoing. This article reviews the available information on eribulin with respect to its clinical pharmacology, pharmacokinetics, pharmacodynamics, mechanism of action, metabolism, preclinical studies, and with special focus on clinical trials.

Pharmacokinetics and excretion of (14)C-lenvatinib in patients with advanced solid tumors or lymphomas

Lenvatinib is an orally available multi-targeted tyrosine kinase inhibitor with anti-angiogenic and antitumor activity. To get more insight into the disposition of lenvatinib, a mass balance study was performed in patients with advanced solid tumors. A single oral 24 mg (100 μCi) dose of (14)C-lenvatinib was administered to six patients, followed by collection of blood, plasma, urine and feces for 7 to 10 days. The collected material was analyzed for total radioactivity, unchanged lenvatinib and selected metabolites. The safety and antitumor effect of a daily oral dose of 24 mg non-labeled lenvatinib were assessed in the extension phase of the study. Peak plasma concentrations of lenvatinib and total radioactivity were reached 1.6 and 1.4 h after administration, respectively, and their terminal phase half-lifes were 34.5 and 17.8 h, respectively. Unchanged lenvatinib systemic exposure accounted for 60 % of the total radioactivity in plasma. Peak concentrations of the analyzed metabolite were over 700-fold lower than the peak plasma concentration of lenvatinib. Ten days after the initial dose, the geometric mean (± CV) recovery of administered dose was 89 % ±10 %, with 64 % ±11 % recovered in feces and 25 % ±18 % in urine. Unchanged lenvatinib in urine and feces accounted for 2.5 % ±68 % of the administered dose, indicating a major role of metabolism in the elimination of lenvatinib. In conclusion, lenvatinib is rapidly absorbed and extensively metabolized, with subsequent excretion in urine and, more predominantly, in feces. Additionally, lenvatinib showed acceptable safety and preliminary antitumor activity.

Population pharmacometric analyses of eribulin in patients with locally advanced or metastatic breast cancer previously treated with anthracyclines and taxanes

Pharmacometric investigation of eribulin was undertaken in patients with metastatic breast cancer (MBC) and other advanced solid tumors. A population pharmacokinetic (PK) model used data combined from seven phase 1 studies (advanced solid tumors; n = 129), and one phase 2 (MBC; n = 211), and one phase 3 study (MBC; n = 173). Phase 3 data were also used in a PK/pharmacodynamic (PD) model of efficacy and tumor response (sum of longest diameters of target lesions). All analyses used NONMEM 7.2. Eribulin PK, described by a dose-independent, three-compartment model with allometric relationship for body weight, was similar for all tumor types. Inter-individual variability (IIV) was 52% for both exposure and clearance. Liver function markers (albumin, alkaline phosphatase, bilirubin) significantly influenced eribulin PK (7.3% of IIV in clearance). Tumor shrinkage correlated with eribulin exposure; a 36% decrease in tumor size from baseline was modeled at week 36. No patient/disease factors significantly predicted eribulin's effect on tumor size. At week 6, a decrease in tumor size was associated with longer survival than an increase (P = .0055), suggesting survival may relate indirectly to eribulin exposure. These pharmacometric analyses provide a detailed overview of eribulin exposure-efficacy relationships to inform physicians treating patients with MBC.

Population pharmacokinetic-pharmacodynamic analysis for eribulin mesilate-associated neutropenia

AIMS

Eribulin mesilate is an inhibitor of microtubule dynamics that is approved for the treatment of late-stage metastatic breast cancer. Neutropenia is one of the major dose-limiting adverse effects of eribulin. The objective of this analysis was to develop a population pharmacokinetic-pharmacodynamic model for eribulin-associated neutropenia.

METHODS

A combined data set of 12 phase I, II and III studies for eribulin mesilate was analysed. The population pharmacokinetics of eribulin was described using a previously developed model. The relationship between eribulin pharmacokinetic and neutropenia was described using a semi-physiological lifespan model for haematological toxicity. Patient characteristics predictive of increased sensitivity to develop neutropenia were evaluated using a simulation framework.

RESULTS

Absolute neutrophil counts were available from 1579 patients. In the final covariate model, the baseline neutrophil count (ANC0) was estimated to be 4.03 × 10(9) neutrophils l(-1) [relative standard error (RSE) 1.2%], with interindividual variability (IIV, 37.3 coefficient of variation % [CV%]). The mean transition time was estimated to be 109 h (RSE 1.8%, IIV 13.9CV%), the feedback constant (γ) was estimated to be 0.216 (RSE 1.4%, IIV 12.2CV%), and the linear drug effect coefficient (SLOPE) was estimated to be 0.0451 μg l(-1) (RSE 3.2%, IIV 54CV%). Albumin, aspartate transaminase and receival of granulocyte colony-stimulating factor (G-CSF) were identified as significant covariates on SLOPE, and albumin, bilirubin, G-CSF, alkaline phosphatase and lactate dehydrogenase were identified as significant covariates on mean transition time.

CONCLUSIONS

The developed model can be applied to investigate optimal treatment strategies quantitatively across different patient groups with respect to neutropenia. Albumin was identified as the most clinically important covariate predictive of interindividual variability in the neutropenia time course.

Pharmacokinetics and excretion of 14C-bendamustine in patients with relapsed or refractory malignancy

BACKGROUND

Bendamustine is an alkylating agent with clinical activity against a variety of hematologic malignancies and solid tumors. To assess the roles of renal and hepatic drug elimination pathways in the excretion and metabolism of bendamustine, a mass balance study was performed in patients with relapsed or refractory malignancies.

METHODS

A single 60-minute intravenous dose of 120 mg/m(2), 80-95 μCi (14)C-bendamustine hydrochloride was administered to six patients, followed by collection of blood, urine, and fecal samples at specified time points up to day 8 or until the radioactivity of the 24-hour urine and fecal collections was below 1% of the administered dose (whichever was longer). Total radioactivity (TRA) was measured in all samples, and concentrations of unchanged bendamustine and its metabolites γ-hydroxy-bendamustine (M3), N-desmethyl-bendamustine (M4), and dihydroxy bendamustine (HP2) were determined in plasma and urine, using validated liquid chromatography-tandem mass spectrometry methods.

RESULTS

The mean recovery of TRA in excreta was 76% of the radiochemical dose. Approximately half of the administered dose was recovered in urine and a quarter in feces. Less than 5% of the administered dose was recovered in urine as unchanged bendamustine. Bendamustine clearance from plasma was rapid, with a half-life of ~40 minutes. Plasma concentrations of M3, M4, and HP2 were very low relative to bendamustine concentrations. Plasma levels of TRA were higher and more sustained as compared with plasma concentrations of bendamustine, M3, M4, and HP2, suggesting the presence of one or more longer-lived (14)C-bendamustine-derived compounds. Fatigue (50%) and vomiting (50%) were the most frequent treatment-related adverse events. A grade 3/4 absolute lymphocyte count decrease occurred in all patients at some point during the study.

CONCLUSION

Bendamustine is extensively metabolized, with subsequent excretion in both urine and feces. Accumulation of bendamustine is not anticipated in cancer patients with renal or hepatic impairment, because of the dose administration schedule and short half-life.

Activity of eribulin mesylate in heavily pretreated breast cancer granted access via the Cancer Drugs Fund

AIM

Eribulin mesylate is a synthetic analog of halichondrin B and is licensed for the treatment of patients with locally advanced or metastatic breast cancer that has progressed following treatment with anthracyclines and taxanes. It was not deemed to be cost effective based on a cost analysis by the National Institute for Health and Care Excellence in England and therefore it is not funded routinely by the National Health Service. The establishment of the Cancer Drugs Fund in England subsequently enabled access. As with any new chemotherapy drug that enters clinical practice for metastatic breast cancer (MBC) it is often used in heavily pretreated patients and the experience in a routine clinical setting can differ from that in a clinical study. We therefore present the experience of the first 25 cases treated at our institution via the Cancer Drugs Fund.

MATERIALS & METHODS

A total of 25 patients were treated and in the 22 assessable cases the objective response rate was 18% (four out of 22), with a clinical benefit rate of 41.0% (9 out of 22).

RESULTS

The median time-to-progression and overall survival were 4.08 months and 5.89 months, respectively. There was a significant difference in clinical benefit rate (odds ratio: 0.065; 95% CI: 0-0.529; p = 0.0055), as well as time-to-progression (hazard ratio: 9.18; 95% CI: 2.26-37.38; p = 0.002 adjusted for age at diagnosis and interval between initial MBC diagnosis and commencing eribulin) favoring those patients who had not been rechallenged. There was no significant difference in overall survival (hazard ratio: 1.16; 95% CI: 0.44-3.05; p = 0.770 adjusted for age at diagnosis and interval between initial diagnosis of MBC and commencing eribulin).

CONCLUSION

Eribulin mesylate shows clinical activity; however, there appears to be differences in terms of benefit in patients based on whether patients have been rechallenged with an anthracycline and/or a taxane. These data require confirmation in larger patient groups.

Pharmacokinetics of eribulin mesylate in patients with solid tumours receiving repeated oral rifampicin

AIM

Eribulin mesylate is a non-taxane microtubule dynamics inhibitor that was recently approved for treatment of metastatic breast cancer. The aim of this study was to determine the effect of rifampicin, a CYP3A4 inducer, on the plasma pharmacokinetics of eribulin in patients with solid tumours.

METHODS

An open-label, non-randomized phase I study was carried out. Patients received intravenous 1.4 mg m(-2) eribulin mesylate on days 1 and 15 and oral rifampicin 600 mg on days 9 to 20 of a 28 day cycle. Pharmacokinetic sampling for determination of eribulin plasma concentrations was performed up to 144 h following administration. AUC(0,∞) and C(max) for eribulin exposure without or with co-administration of rifampicin were subjected to an analysis of variance (anova) and corresponding 90% confidence intervals (CI) were calculated. Subsequently, patients were allowed to continue eribulin mesylate treatment with 1.4 mg m(-2) eribulin mesylate on days 1 and 8 of a 21 day cycle. Also the adverse event profile and anti-tumour activity were assessed.

RESULTS

Fourteen patients were included and 11 patients were evaluable for pharmacokinetic analysis. Co-administration of rifampicin had no effect on single dose exposure to eribulin (geometric least square means ratio: AUC(0,∞) = 1.10, 90% CI 0.91, 1.34 and C(max) = 0.97, 90% 0.81, 1.17). The most common treatment-related grade ≥3 adverse events were grade 3 neutropenia (4/14, 29%), leucopenia and fatigue (both 3/14, 21%).

CONCLUSIONS

These results indicate that eribulin mesylate may be safely co-administered with compounds that are CYP3A4 inducers.