Effect of a proton pump inhibitor on the pharmacokinetics of imatinib

Tyrosine kinase inhibitors in cancers: Treatment optimization - Part II

Real-life populations are more heterogeneous than those included in prospective clinical studies. In cancer patients, comorbidities and co-medications favor the appearance of severe adverse effects which can significantly impact quality of life and treatment effectiveness. Most of tyrosine kinase inhibitors (TKI) have been developed with flat oral dosing exposing patients to the risk of poor adherence due to side effects. Additionally, genetic or physiological factors, differences in diet, and drug-drug interactions can lead to inter-individual variability affecting treatment outcomes and increasing the risk of adverse events. Knowledge of the different factors of variability allows individualized patient management. This review examines the effects of adherence, food intake, and pharmaceutical form on the pharmacokinetics of oral TKI, as well as evaluating pharmacokinetics considerations improving TKI management. Concentration-effectiveness and concentration-toxicity data are presented for the selected TKI, and a simple therapeutic drug monitoring schema is outlined to help individualize dosing of oral TKI.

Proton pump inhibitors and cancer treatments: Emerging evidence against coadministration

BACKGROUND

Proton pump inhibitors (PPIs) are widely used in cancer patients despite accumulating data showing that they can impact the efficacy of major anticancer drugs. This is particularly important with tyrosine kinase inhibitors (TKIs) and immune checkpoint inhibitors (CPIs).

RESULTS

Most TKIs require gastric acidity for their absorption and some retrospective series demonstrated that coprescription decreases the survival benefit of some TKI use (erlotinib, gefitinib and pazopanib). Relations between microbiota, the immune system, and the efficacy of immunotherapy are now obvious, just as modifications to gut flora after PPIs use are well-known. Many retrospective articles, including articles based on individual-participant data from randomized studies, demonstrated that patients treated with CPIs have a poorer outcome (overall survival, progression-free survival and response rate) when they received PPIs concomitantly, while there was no impact of such coprescription among patients in control arms, not treated with immunotherapies. Similar data were also observed in patients treated with palbociclib.

CONCLUSION

For these interactions, it is very important to use the precautionary principle and warn patients and physicians about this. In patients who require acid suppression because of severe symptoms, using antacids or H2 blockers could be recommended.

Evaluation of Systemic Treatment Options for Gastrointestinal Stromal Tumours

Gastrointestinal stromal tumours (GIST) are the most common mesenchymal tumours of the gastrointestinal tract. Surgical treatment is recommended for the majority of localised GIST, while systemic treatment is the cornerstone of management for metastatic or unresectable disease. While a three-year regimen of imatinib is the standard of care in the adjuvant setting, there is no precise recommendation for the duration of neoadjuvant treatment, where imatinib is usually given between 4 and 12 months. Continuous treatment with imatinib at a dose of 400 mg once per day is recommended for most patients with unresectable or metastatic GIST in the first line. An exception is represented by patients with tumours harbouring the imatinib-insensitive PDGFRA D842V mutation who would be better treated with avapritinib. Targeted therapies are also recommended in the presence of NTRK rearrangements and BRAF mutations, although limited data are available. While an increase in the dose of imatinib to 800 mg is an option for the second line, sunitinib is usually considered the standard of care. Similar outcomes were reported for ripretinib in patients with tumours harbouring KIT exon 11 mutation, with significantly fewer side effects. Regorafenib and ripretinib are the standards of care in the third and fourth lines, respectively. The recent development of various systemic treatment options allows for a more personalised approach based on the molecular profile of the GIST, patient characteristics, and the profile of medications' adverse events. A multidisciplinary approach is paramount since combining systemic treatment with locoregional treatment options and supportive care is vital for long-term survival.

The status of TKI/acid-suppressant concomitant use in 44 hospitals in China: A cross-sectional descriptive study

The irrational use of tyrosine kinase inhibitors (TKIs) has attracted increasing attention, especially because of drug-drug interactions. The objective of this study was to analyze TKI prescriptions and evaluate the rationality of concomitant use of TKIs and acid-suppressants. TKI prescriptions from 2016 to 2018 were collected from hospitals in Beijing, Guangzhou, Hangzhou, and Zhengzhou for 40 d/yr. Focusing on the data in 2018, we analyzed the pharmacoeconomic indicators of TKIs and the number and proportion of different coprescriptions. The evaluation criteria for coprescriptions were based on clinical literature and package inserts. A total of 41,738 TKI prescriptions were assessed. The total dose and sales of imatinib were the highest, the medication days and defined daily doses of gefitinib were the highest, and the highest defined daily cost was sunitinib. Meanwhile, there were 17 TKIs with drug utilization indices of ≤ 1.0. The irrational combination rate of prescriptions of non-cancer-related departments was high in 3 cities, but not Hangzhou. The irrational combination rate of prescription of inpatient prescriptions was > 23% in the 4 cities. The combined use of TKIs and acid-suppressants is common in China and may have a clear or potential impact on the pharmacokinetics, pharmacodynamics, and adverse drug reactions of TKIs. Therefore, it is urgent to implement necessary interventions to stop such irrational use or if the combined use is necessary, to correct adverse consequences. The aims should be to achieve safe and effective use of TKIs and reduce unnecessary costs.

Applications, Challenges, and Outlook for PBPK Modeling and Simulation: A Regulatory, Industrial and Academic Perspective

Several regulatory guidances on the use of physiologically based pharmacokinetic (PBPK) analyses and physiologically based biopharmaceutics model(s) (PBBM(s)) have been issued. Workshops are routinely held, demonstrating substantial interest in applying these modeling approaches to address scientific questions in drug development. PBPK models and PBBMs have remarkably contributed to model-informed drug development (MIDD) such as anticipating clinical PK outcomes affected by extrinsic and intrinsic factors in general and specific populations. In this review, we proposed practical considerations for a "base" PBPK model construction and development, summarized current status, challenges including model validation and gaps in system models, and future perspectives in PBPK evaluation to assess a) drug metabolizing enzyme(s)- or drug transporter(s)- mediated drug-drug interactions b) dosing regimen prediction, sampling timepoint selection and dose validation in pediatric patients from newborns to adolescents, c) drug exposure in patients with renal and/or and hepatic organ impairment, d) maternal-fetal drug disposition during pregnancy, and e) pH-mediated drug-drug interactions in patients treated with proton pump inhibitors/acid-reducing agents (PPIs/ARAs) intended for gastric protection. Since PBPK can simulate outcomes in clinical studies with enrollment challenges or ethical issues, the impact of PBPK models on waivers and how to strengthen study waiver is discussed.

Proton Pump Inhibitors and Cancer: Current State of Play

Background: Proton pump inhibitors (PPIs) are one of the most widely used drugs worldwide and are overprescribed in patients with cancer; there is increasing evidence of their effects on cancer development and survival. The objective of this narrative review is to comprehensively identify cancer medications that have clinically meaningful drug–drug interactions (DDIs) with PPIs, including loss of efficacy or adverse effects, and to explore the association between PPIs and cancer.

Methods: A PubMed search of English language studies published from 1 January 2016, to 1 June 2021 was conducted. The search terms included “proton pump inhibitors,” “cancer,” “chemotherapy,” “immunotherapy,” “hormonotherapies,” “targeted therapies,” “tyrosine kinase inhibitors,” and “gut microbiome”. Recent and relevant clinical trials, meta-analyses, and reviews were included.

Results: PPIs may have pro-tumor activity by increasing plasma gastrin levels or anti-tumor activity by inhibiting V-ATPases. However, their impact on cancer survival remains unclear. PPIs may decrease the efficacy of some antineoplastic agents through direct DDIs (e.g., some tyrosine kinase inhibitors, capecitabine, irinotecan, methotrexate). More complex DDIs seem to exist for immunotherapies with indirect interactions through the microbiome. PPIs worsen hypomagnesemia, bone loss, iron, and vitamin B12 deficiencies but may have a protective effect on the renal system.

Discussion/Conclusions: PPIs may interact with the cancer microbiome and the efficacy of various antineoplastic agents, although only a few DDIs involving PPIs are clinically significant. Further pharmaco-epidemiological studies are warranted, but physicians should be aware of the potential consequences of PPI use, which should be dose appropriate and prescribed according to guidelines.

Controversial link between proton pump inhibitors and anticancer agents: review of the literature

Drug-drug interactions represent a topic of great interest, not only due to the risk of unexpected adverse events but also due to the possibility of altering the effectiveness of a specific treatment. Inappropriate or concomitant use of drugs can often lead to changes in the bioavailability of various compounds, resulting in pharmacokinetic alterations. A recent example is the concomitant administration of proton pump inhibitors (PPIs) and anticancer agents. PPIs are overused beyond their classic indications, resulting in a high risk of interactions with other drugs, such as anticancer agents, both PO and intravenous. However, the real clinical impact of concomitant acid suppression therapy and anticancer therapies remains controversial and is not yet fully understood. Certainly, the gut microbiota plays a key role in regulating the response of the immune system, and PPIs can significantly alter the gut microbiome, resulting in gut dysbiosis. Indeed, while the link sometimes appears to lead to negative outcomes, as in the case of immunotherapy, oral capecitabine, or tyrosine kinase inhibitors, in other cases, it seems to enhance the effectiveness of intravenous chemotherapy. In this review, I analyse the possible drug interactions between PPIs and the main classes of anticancer drugs.

Pharmacokinetic effects of proton pump inhibitors on the novel PARP inhibitor fluzoparib: a single-arm, fixed-sequence trial in male healthy volunteers

Purpose To assess the pharmacokinetic (PK) effect of proton pump inhibitors on the novel poly(adenosine diphosphate-ribose) polymerase (PARP) inhibitor fluzoparib, and observe the safety of its co-administration with omeprazole. Patients and methods Sixteen male healthy volunteers (HVs) were enrolled in a single-center, single-arm, open-label, fixed-sequence study. HVs took fluzoparib (100 mg, p.o.) after meal consumption on day-1, took omeprazole 40 mg (p.o.) under a fasting condition from day-5 to day-9, and took fluzoparib (100 mg, p.o.) after meal consumption on day-9. Blood samples were collected at predetermined timepoints for PK analyses. Safety was assessed via clinical laboratory tests. The study was registered with the Clinical Trials Registry on 30 September 2019 (NCT04108676). Results The peak plasma concentrations (Cmax) after fluzoparib administration was 2395.17 ± 418.27 ng/mL, the area under the curve (AUC) within 72 h (AUC0 - 72 h) was 26669.09 ± 7320.12 h·ng/mL, and AUC0-∞ was 26897.44 ± 7573.61 h·ng/mL. The Cmax after co-administration of fluzoparib and omeprazole was 2489.43 ± 423.72 ng·mL, AUC0 - 72 h was 30300.49 ± 8350.08 h·ng/mL, and AUC0-∞ was 30678.74 ± 8595.55 h·ng/mL. The geometric mean ratio of Cmax, AUC0 - 72 h and AUC0-∞ was 104.0% (90%CI: 94.8-114.0%), 113.6% (104.2-123.9%) and 104.1% (104.5-124.6%). The number of HVs with adverse reactions was identical (eight) for administration of fluzoparib and co-administration of fluzoparib and omeprazole. Conclusions The proton pump inhibitor omeprazole did not have a significant influence on the PK behavior of fluzoparib, and its safety profile was good upon co-administration with omeprazole. (NCT04108676, 30 September 2019).

Treatment of Metastatic Gastrointestinal Stromal Tumors (GIST): A Focus on Older Patients

Gastrointestinal stromal tumors (GIST) originating in the Cajal cells are the most common mesenchymal neoplasms of the gastrointestinal tract. The median age of patients with this diagnosis is 65 years, and over 20% of cases affect people over the age of 70 years. The effectiveness and tolerability of systemic treatment with tyrosine kinase inhibitors in older patients with GIST seem to be similar to that in younger patients, but some studies have shown that treatment of older patients is suboptimal. Disability, frailty, comorbidities, and concomitant medications may influence treatment decisions, and toxicities also more often lead to treatment discontinuation. The known safety profile and oral administration route of the tyrosine kinase inhibitors used in GIST may allow maximization of treatment and the best efficacy, especially in older patients. This review summarizes the efficacy data for the systemic treatment of GIST, including data for older patients and from real-world experiences, if available and significant. The reported safety data and general rules for toxicity management, including appropriate patient selection and the need for careful monitoring during treatment, are also discussed.

A Minimal Information Model for Potential Drug-Drug Interactions

Despite the significant health impacts of adverse events associated with drug-drug interactions, no standard models exist for managing and sharing evidence describing potential interactions between medications. Minimal information models have been used in other communities to establish community consensus around simple models capable of communicating useful information. This paper reports on a new minimal information model for describing potential drug-drug interactions. A task force of the Semantic Web in Health Care and Life Sciences Community Group of the World-Wide Web consortium engaged informaticians and drug-drug interaction experts in in-depth examination of recent literature and specific potential interactions. A consensus set of information items was identified, along with example descriptions of selected potential drug-drug interactions (PDDIs). User profiles and use cases were developed to demonstrate the applicability of the model. Ten core information items were identified: drugs involved, clinical consequences, seriousness, operational classification statement, recommended action, mechanism of interaction, contextual information/modifying factors, evidence about a suspected drug-drug interaction, frequency of exposure, and frequency of harm to exposed persons. Eight best practice recommendations suggest how PDDI knowledge artifact creators can best use the 10 information items when synthesizing drug interaction evidence into artifacts intended to aid clinicians. This model has been included in a proposed implementation guide developed by the HL7 Clinical Decision Support Workgroup and in PDDIs published in the CDS Connect repository. The complete description of the model can be found at https://w3id.org/hclscg/pddi.

Proton Pump Inhibitors and Oncologic Treatment Efficacy: A Practical Review of the Literature for Oncologists

Proton pump inhibitors (PPIs) are the most commonly used anti-acid drugs worldwide, including among cancer patients. However, drug-drug interactions between PPIs and other agents may lead to decreased drug absorption with possible reduced therapeutic benefit, or even increased toxicity. Unfortunately, only scarce data exist regarding the safety of concomitant PPI use with anti-cancer agents. We aim at reviewing current evidence on this possible interaction by dividing anti-cancer agents by class. Until further data is available, we encourage healthcare providers to limit unnecessary PPI overuse.

Impact of Use of Gastric-Acid Suppressants and Oral Anti-Cancer Agents on Survival Outcomes: A Systematic Review and Meta-Analysis

We performed a systematic review and meta-analysis to evaluate the role of gastric acid suppressant use on outcomes of tyrosine kinase inhibitors (TKIs) and oral chemotherapy. We identified all research evaluating the effect of GAS (gastric acid suppressants) use on patients receiving oral chemotherapy or TKIs for solid tumors. The pooled hazard ratios (HRs) and 95% confidence interval (95%CI) for overall survival (OS) and progression-free survival (PFS) were calculated with a fixed-effects or a random effects model. The study population included n = 16 retrospective studies and 372,418 patients. The series concerned gastrointestinal tract tumors (n = 5 studies), renal cell carcinomas (RCC, n = 3 studies), non-small cell lung cancers (NSCLC, n = 5 studies), and soft tissue sarcomas or mixed histologies solid tumors in n = 3 studies. The pooled HRs for OS and PFS were 1.31 (95%CI: 1.20-1.43; p < 0.01) and 1.3 (95%CI 1.07-1.57; p < 0.01) for GAS and no GAS users, respectively. Only studies of EGFR (epidermal growth factor receptor) mutated NSCLC patients receiving TKIs and those with colorectal cancer receiving oral chemotherapy showed a significant correlation between GAS and poor survival. Our study supports the evidence of a possible negative impact of concomitant GAS therapy on survival outcomes of patients receiving oral anti-cancer drugs.

[Proton pump inhibitors and cancers: A hazardous association?]

Proton pump inhibitors, a major progress in gastro-enterology, are globally among the most widely prescribed drugs. But, due to their strong gastric acid inhibition, they can be responsible for side effects, particularly in cancer patients. They are involved in renal function impairment, bone fractures, digestive bacterial overgrowth, particularlyclostridium difficile infections, anemia and hypomagnesemia. Long term use can increase the risks of gastric, pancreatic and liver cancers. They decrease absorption of weak bases drugs, particularly tyrosine kinase inhibitors and capecitabine and are responsible for a poorer prognosis if taken concomitantly with erlotinib, gefitinib and pazopanib. Modification of cyclin dependent kinases is also possible as well as decrease of efficacy of immune check point inhibitors (microbiome modifications). Absoption and efficacy of capecitabine seem also poorer with negative prognosis effect on treatment of gastric and colon cancer. Their long term use, particularly in cancer patients, should probably be avoided.

Pivotal Considerations for Optimal Deployment of Healthy Volunteers in Oncology Drug Development

Oncology drug development is among the most challenging of any therapeutic area, with first-in-human trials expected to deliver information on both safety and activity. Until recently, therapeutic approaches in oncology focused on cytotoxic chemotherapy agents, ruling out even the possibility of enrolling normal healthy volunteers (NHVs) in clinical trials due to safety considerations. The emergence of noncytotoxic modalities, including molecularly targeted agents with more favorable safety profiles, however, has led to increasing numbers of clinical pharmacology studies of these agents being conducted in NHVs. Beyond rapid enrollment and cost savings, there are other advantages of conducting specific types of studies in NHVs with the goal of more appropriate dosing decisions in certain subsets of the intended patient populations, allowing for enrollment of such patients in therapeutic trials from which they might otherwise have been excluded. Nevertheless, the decision must be carefully weighed against potential disadvantages, and although the considerations surrounding conduct of clinical trials using NHVs are generally well-defined in most other therapeutic areas, they are less well-defined in oncology.

The effect of gastrectomy on regorafenib exposure and progression-free survival in patients with advanced gastrointestinal stromal tumours

Aims

We investigated whether major gastrectomy influences the plasma exposure of regorafenib and treatment outcome.

Methods

Efficacy and pharmacokinetic data from 133 gastrointestinal stromal tumour patients included in a phase III trial were analysed. Patients were subdivided into 2 groups according to the extent of the gastrectomy (no/nonsignificant gastrectomy and major gastrectomy). Progression‐free survival (PFS) on regorafenib was measured and regorafenib and its pharmacological active metabolites plasma exposure were measured.

Results

A total of 133 patient were included, of whom 27 underwent major gastrectomy. In patients with no/nonsignificant gastrectomy the median PFS was 145 (interquartile range 43–281) days. The PFS in patients with a major gastrectomy was 172 (interquartile range 57–280) days. Regorafenib pharmacokinetic samples were collected in 80 patients of which 19 patients with a major gastrectomy and 61 patients with no/nonsignificant gastric surgery. The average ± standard deviation total concentration of regorafenib including the metabolites M‐2 and M‐5 was 6.9 ± 1.53 μmol/L and 6.7 ± 1.56 μmol/L in patient with major gastrectomy and no/nonsignificant gastrectomy respectively.

Conclusion

Our study shows that major gastrectomy did not influence plasma exposure of regorafenib and metabolites. In addition, no difference in PFS between the subgroups was seen.

Clinically relevant drug interactions with multikinase inhibitors: a review

Multikinase inhibitors (MKIs), including the tyrosine kinase inhibitors (TKIs), have rapidly become an established factor in daily (hemato)-oncology practice. Although the oral route of administration offers improved flexibility and convenience for the patient, challenges arise in the use of MKIs. As MKIs are prescribed extensively, patients are at increased risk for (severe) drug–drug interactions (DDIs). As a result of these DDIs, plasma pharmacokinetics of MKIs may vary significantly, thereby leading to high interpatient variability and subsequent risk for increased toxicity or a diminished therapeutic outcome. Most clinically relevant DDIs with MKIs concern altered absorption and metabolism. The absorption of MKIs may be decreased by concomitant use of gastric acid-suppressive agents (e.g. proton pump inhibitors) as many kinase inhibitors show pH-dependent solubility. In addition, DDIs concerning drug (uptake and efflux) transporters may be of significant clinical relevance during MKI therapy. Furthermore, since many MKIs are substrates for cytochrome P450 isoenzymes (CYPs), induction or inhibition with strong CYP inhibitors or inducers may lead to significant alterations in MKI exposure. In conclusion, DDIs are of major concern during MKI therapy and need to be monitored closely in clinical practice. Based on the current knowledge and available literature, practical recommendations for management of these DDIs in clinical practice are presented in this review.

Crenolanib is a type I tyrosine kinase inhibitor that inhibits mutant KIT D816 isoforms prevalent in systemic mastocytosis and core binding factor leukemia

Activating D816 mutations of the class III receptor tyrosine kinase KIT are associated with the majority of patients with systemic mastocytosis (SM), but also core binding factor (CBF) AML, making KIT mutations attractive therapeutic targets for the treatment of these cancers.

Crenolanib is a potent and selective inhibitor of wild-type as well as mutant isoforms of the class III receptor tyrosine kinases FLT3 and PDGFRα/β. Notably, crenolanib inhibits constitutively active mutant-FLT3 isoforms resulting from amino acid substitutions of aspartic acid at codon 835, which is homologous to codon 816 in the KIT gene - suggesting sensitivity against mutant-KIT D816 isoforms as well.

Here we demonstrate that crenolanib targets KIT D816 in SM and CBF AML models: crenolanib inhibits cellular proliferation and initiates apoptosis of mastocytosis cell lines expressing these mutations. Target-specificity was confirmed using an isogenic cell model. In addition, we demonstrate that KIT D816 mutations are targetable with clinically achievable doses of crenolanib. Further, a rationale to combine cladribine (2-CDA), the therapeutic standard in SM, with crenolanib is provided.

In conclusion, we demonstrate that crenolanib is an inhibitor of mutant-KIT D816 isoforms at clinically achievable concentrations, and thus may be a potential treatment for SM and CBF AML as a monotherapy or in combination approaches.

Managing Drug Interactions in Cancer Therapy: A Guide for the Advanced Practitioner

Mrs. P is a 30-year-old woman who presented to our bone marrow transplant program with myelodysplastic syndrome (MDS). She received a haploidentical allogeneic stem cell transplant with a conditioning regimen consisting of busulfan and cyclophosphamide. This treatment was followed by post-transplant immunosuppression for graft-versus-host disease (GVHD) with cyclophosphamide, mycophenolate mofetil (MMF), and tacrolimus (see Table 1 for medication list). Tacrolimus levels were monitored twice a week with adjustment to a goal range of between 5 and 10 ng/mL. We initiated tacrolimus at a dose of 0.03 mg/kg by mouth twice daily (rounded to 2 mg by mouth twice daily). Drug interactions were assessed by the clinical pharmacist prior to admission, routinely with medication changes, and then upon discharge.

Drug-drug interactions with imatinib: An observational study

Many patients treated with imatinib, used in cancer treatment, are using several other drugs that could interact with imatinib. Our aim was to study all the drug-drug interactions (DDIs) observed in patients treated with imatinib.We performed 2 observational studies, between the 1st January 2012 and the 31st August 2015 in the Midi-Pyrénées area (South Western France), using the French health insurance reimbursement database and then the French Pharmacovigilance Database (FPVD).A total of 544 patients received at least 1 reimbursement for imatinib. Among them, 486 (89.3%) had at least 1 drug that could potentially interact with imatinib. Paracetamol was the most frequent drug involved (77.4%). Proton pump inhibitors, dexamethasone and levothyroxine, were found in >10% of patients. In the FPVD, among a total of 25 reports of ADRs with imatinib recorded in the Midi-Pyrénées area, 10 (40%) had potential DDIs with imatinib. Imatinib was most frequently prescribed by hospital physicians and drugs interacting with imatinib, by general practitioners.Our study showed that at least 40% of the patients treated with imatinib were at risk of DDIs and that all prescribers must be cautious with DDIs in patients treated with imatinib. During imatinib treatment, we particularly recommend to limit the dose of paracetamol at 1300 mg per day, to avoid the use of dexamethasone, and to double the dose of levothyroxine.

Effect of food and acid-reducing agents on the absorption of oral targeted therapies in solid tumors

Oral targeted therapies represent an increasingly important group of drugs within modern oncology. With the shift from intravenously to orally administered drugs, drug absorption is a newly introduced factor in drug disposition. The process of absorption can have a large effect on inter- and intrasubject variability in drug exposure and thereby potentially treatment benefit or the severity of toxicities. The intake of oral targeted therapies with food and concomitant use of acid-reducing agents (ARAs) can significantly affect drug absorption. The size and direction of the effect of food and ARAs on drug absorption varies among drugs as a result of different chemical characteristics. Therefore, an awareness and understanding of these effects for each drug is essential to optimize patient outcomes.

Population Pharmacokinetic Analysis of the Oral Absorption Process and Explaining Intra-Subject Variability in Plasma Exposures of Imatinib in Healthy Volunteers

BACKGROUND AND OBJECTIVE

Imatinib mesylate is presently the first-line treatment for chronic myeloid leukemia (CML). The aim of this study was to investigate the absorption and distribution kinetics of imatinib in healthy Iranian volunteers using nonlinear mixed effects modeling (NLMEM) to assess the overall, intra- and inter-subject variabilities in pharmacokinetic parameters after oral administration.

METHODS

This analysis was based on data from 24 healthy subjects who participated in a bioequivalence study after administering a single dose of 200 mg of each formulation. Imatinib concentrations were quantified using a validated liquid chromatography method. To simultaneously describe the imatinib pharmacokinetic profiles obtained with both formulations, a population pharmacokinetic model was applied to data using SAEM algorithm implemented in MONOLIX, whilst simulations were used by numerical solving of ordinary differential equations to calculate secondary parameters in individuals for bioequivalence studies.

RESULTS

According to goodness-of-fit criteria, a two-compartment open model with sequential zero- then first-order absorption and first-order elimination was used as the structural pharmacokinetic model. Inter-individual variability (IIV) was considered for all parameters. Typical population estimates (% IIV) were fraction of the drug absorbed with a zero-order kinetic (Fr) of 0.153 (47.9 %) in period (Tk0) of 0.714 h (47.4 %), first-order absorption rate constant (k a) of 0.94 h(-1)(31.2 %), oral clearance of 19 L/h (27.9 %), central volume of distribution (V c/F) of 139 L (21.5 %), apparent peripheral volume of distribution (V p/F) of 130 L (29.7 %) and the apparent inter-compartment clearance (Q/F) of 29.6 L/h (41.8 %). Body mass index (BMI) was the only covariate found to significantly affect V p /F. The coefficient of variation for intra-individual plasma exposure (AUC0-∞) was 27.8 %.

CONCLUSIONS

Analyses using NLMEM for imatinib exhibited absorption complexities such as two input rates and medium to high intra-individual variability in drug exposure.

Variability in bioavailability of small molecular tyrosine kinase inhibitors

Small molecular tyrosine kinase inhibitors (smTKIs) are in the centre of the very quickly expanding area of personalized chemotherapy and oral applicability thereof. The number of drugs in this class is rapidly growing, with twenty current approvals by both the European Medicines Agency (EMA) and the Food and Drug Administration (FDA). The drugs are, however, generally characterized by a poor oral, and thus variable, bioavailability. This results in significant variation in plasma levels and exposure. The cause is a complex interplay of factors, including poor aqueous solubility, issued permeability, membrane transport and enzymatic metabolism. Additionally, food and drug-drug interactions can play a significant role. The issues related with an impaired bioavailability generally receive little attention. To the best of our knowledge, this article is the first to provide an overview of the factors that determine the bioavailability of the smTKIs.

Drug-drug interactions with tyrosine-kinase inhibitors: a clinical perspective

In the past decade, many tyrosine-kinase inhibitors have been introduced in oncology and haemato-oncology. Because this new class of drugs is extensively used, serious drug-drug interactions are an increasing risk. In this Review, we give a comprehensive overview of known or suspected drug-drug interactions between tyrosine-kinase inhibitors and other drugs. We discuss all haemato-oncological and oncological tyrosine-kinase inhibitors that had been approved by Aug 1, 2013, by the US Food and Drug Administration or the European Medicines Agency. Various clinically relevant drug interactions with tyrosine-kinase inhibitors have been identified. Most interactions concern altered bioavailability due to altered stomach pH, metabolism by cytochrome P450 isoenzymes, and prolongation of the QTc interval. To guarantee the safe use of tyrosine-kinase inhibitors, a drugs review for each patient is needed. This Review provides specific recommendations to guide haemato-oncologists, oncologists, and clinical pharmacists, through the process of managing drug-drug interactions during treatment with tyrosine-kinase inhibitors in daily clinical practice.

Effect of gastrointestinal resection on sunitinib exposure in patients with GIST

Background

GIST patients often undergo GI-surgery. Previous studies have shown that imatinib and nilotinib exposures were decreased in GIST patients with prior major gastrectomy. We investigated whether major gastrectomy influences the exposure to sunitinib and its active metabolite SU12662.

Methods

Pharmacokinetic data from 305 GIST patients included in 4 phase I-III trials were analyzed. Patients were subdivided into 6 groups according to their prior GI-surgery. Apparent clearance (CL/F) and dose-corrected steady-state plasma exposures (AUC_24,ss) of sunitinib and SU12662 were estimated using a population PK approach. ANCOVA was performed to test for differences in AUC_24,ss and CL/F between each surgery subgroup and controls.

Results

Major gastrectomy did not influence sunitinib or SU12662 exposure. The geometric mean of sunitinib and SU12662 AUC_24,ss was decreased by 21% and 28% in patients with both gastrectomy and small bowel resection (n = 8) compared to controls (n = 63) for sunitinib (931 ng*hr/mL (95%-CI; 676–1283) versus 1177 ng*hr/mL (95%-CI; 1097–1263); p < 0.05) and SU12662 (354 ng*hr/mL (95%-CI; 174–720) versus 492 ng*hr/mL (95%-CI; 435–555); p < 0.05). No significant differences in exposure were observed in each of the other subgroups versus controls.

Conclusion

In contrast to previous results for imatinib and nilotinib, gastrectomy alone does not influence sunitinib or SU12662 exposure. This should be taken into account for the treatment of gastrectomized GIST patients with TKIs. In patients who had undergone both gastrectomy and small bowel resection, sunitinib and SU12662 exposures are significantly, although clinically not relevantly, decreased.

Clinical efficacy of generic imatinib

Background

Generic imatinib has recently been approved for chronic myeloid leukemia in Canada and the European Union (EU). There are anecdotal concerns of reduced efficacy related to generic vs. brand name imatinib.

Methods

MEDLINE and EMBASE were searched. Generic imatinib product monographs approved by Health Canada and the European Medicines Agency (EMA) were reviewed. Medical information of Novartis, Teva and Apotex were contacted.

Results

Several issues have been raised. First, generic imatinib approved outside Canada and the European Union has been associated with reduced efficacy in small case reports and contradictory findings with two case series. However, the clinical bioequivalence of these generic products has not been clearly established. Secondly, use of generic imatinib in other populations has been questioned. However, imatinib absorption is not significantly different in pediatric chronic myeloid leukemia or patients with gastrointestinal tumours compared to adults with chronic myeloid leukemia. Although reduced absorption was reported after gastric bypass and gastrectomy, imatinib absorption occurs mostly in the ileum, duodenum, colon and jejunum. Change in gastric acidity has also been shown to not affecting imatinib absorption. Finally, beta-crystal form of brand name imatinib is more stable than the alpha-crystal form of generic imatinib at room temperature. However, the EMA found both crystal forms to be highly soluble and polymorphism would not significantly influence the performance of generic imatinib.

Conclusion

Overall, anecdotal concerns appear to be unfounded for generic imatinib approved in Canada and the EU. There is no evidence that these generic imatinib products are less effective than brand name imatinib.

A clinical study to examine the potential effect of lansoprazole on the pharmacokinetics of bosutinib when administered concomitantly to healthy subjects

BACKGROUND

Bosutinib is an orally bioavailable, dual Src and Abl tyrosine kinase inhibitor approved in the USA for the treatment of Philadelphia chromosome-positive chronic myeloid leukemia following development of resistance or intolerance to prior therapy. In vitro studies demonstrated that bosutinib displays pH-dependent aqueous solubility, suggesting that concomitant administration of agents that alter gastric pH could affect bosutinib absorption.

OBJECTIVES

The objectives of this study were to evaluate the effect of lansoprazole, a gastric proton pump inhibitor, on the pharmacokinetics and safety of bosutinib.

METHODS

This open-label, non-randomized, phase I study involved inpatients and outpatients at a single site. The study participants were healthy men or women of non-childbearing potential aged 18-50 years. Each subject received bosutinib 400 mg on Day 1, lansoprazole 60 mg on Day 14, and bosutinib 400 mg co-administered with lansoprazole 60 mg on Day 15 under fasting conditions. The main outcome measure was the effect of multiple doses of lansoprazole on the pharmacokinetic profile of a single oral dose of bosutinib.

RESULTS

A total of 24 healthy male subjects were enrolled. Co-administration with lansoprazole decreased the mean maximum plasma concentration (C(max)) of bosutinib from 70.2 to 42.9 ng/mL, and the total area under the plasma concentration-time curve (AUC) from 1,940 to 1,470 ng·h/mL. Log-transformed bosutinib pharmacokinetic parameters indicated significant between-treatment differences; the least squares geometric mean ratio for C(max) was 54 % (95 % CI 42-70) and for AUC was 74 % (95 % CI 60-90). Mean apparent total body clearance from plasma after oral administration increased from 237 to 330 L/h, and the median time to reach Cmax increased from 5 to 6 h, although this change may be related to decreased bosutinib absorption when combined with lansoprazole. When co-administered with lansoprazole, bosutinib maintained an acceptable safety profile, which was primarily characterized by diarrhea (33 %), headache (21 %), and nausea (13 %). One subject experienced serious adverse events of diverticulitis, gastritis, and duodenitis after co-administration; however, no participant withdrew because of toxicity.

CONCLUSIONS

This study demonstrated that bosutinib absorption may be reduced when co-administered with lansoprazole or other proton pump inhibitors. Caution should be used with such drug combinations, as subtherapeutic exposure of bosutinib may limit its clinical antitumor activity; short-acting antacids are recommended instead.

Prevalence of acid-reducing agents (ARA) in cancer populations and ARA drug-drug interaction potential for molecular targeted agents in clinical development

Acid-reducing agents (ARAs) are the most commonly prescribed medications in North America and Western Europe. There are currently no data describing the prevalence of their use among cancer patients. However, this is a paramount question due to the potential for significant drug-drug interactions (DDIs) between ARAs, most commonly proton pump inhibitors (PPIs), and orally administered cancer therapeutics that display pH-dependent solubility, which may lead to decreased drug absorption and decreased therapeutic benefit. Of recently approved orally administered cancer therapeutics, >50% are characterized as having pH-dependent solubility, but there are currently no data describing the potential for this ARA-DDI liability among targeted agents currently in clinical development. The objectives of this study were to (1) determine the prevalence of ARA use among different cancer populations and (2) investigate the prevalence of orally administered cancer therapeutics currently in development that may be liable for an ARA-DDI. To address the question of ARA use among cancer patients, a retrospective cross-sectional analysis was performed using two large healthcare databases: Thomson Reuters MarketScan (N = 1,776,443) and the U.S. Department of Veterans Affairs (VA, N = 1,171,833). Among all cancer patients, the total prevalence proportion of ARA use (no. of cancer patients receiving an ARA/total no. of cancer patients) was 20% and 33% for the MarketScan and VA databases, respectively. PPIs were the most commonly prescribed agent, comprising 79% and 65% of all cancer patients receiving a prescription for an ARA (no. of cancer patients receiving a PPI /no. of cancer patients receiving an ARA) for the MarketScan and VA databases, respectively. To estimate the ARA-DDI liability of orally administered molecular targeted cancer therapeutics currently in development, two publicly available databases, (1) Kinase SARfari and (2) canSAR, were examined. For those orally administered clinical candidates that had available structures, the pKa's and corresponding relative solubilities were calculated for a normal fasting pH of 1.2 and an "ARA-hypochlorhydric" pH of 4. Taking calculated pKa's and relative solubilities into consideration, clinical candidates were classified based on their risk for an ARA-DDI. More than one-quarter (28%) of the molecules investigated are at high risk for an ARA-DDI, and of those high risk molecules, nearly three-quarters (73%) are being clinically evaluated for at least one of five cancer types with the highest prevalence of ARA use (gastrointestinal, pancreatic, lung, glioblastoma multiforme, gastrointestinal stromal tumor (GIST)). These data strongly suggest that with the clinical development of ARA-DDI-susceptible cancer therapeutics will come continued challenges for drug-development scientists, oncologists, and regulatory agencies in ensuring that patients achieve safe and efficacious exposures of their cancer therapeutics and thus optimal patient outcomes.

Drug interactions with solid tumour-targeted therapies

Drug interactions are an on-going concern in the treatment of cancer, especially when targeted therapies, such as tyrosine kinase inhibitors (TKI) or mammalian target of rapamycin (mTOR) inhibitors, are being used. The emergence of elderly patients and/or patients with both cancer and other chronic co-morbidities leads to polypharmacy. Therefore, the risk of drug-drug interactions (DDI) becomes a clinically relevant issue, all the more so as TKIs and mTOR inhibitors are essentially metabolised by cytochrome P450 enzymes. These DDIs can result in variability in anticancer drug exposure, thus favouring the selection of resistant cellular clones or the occurrence of toxicity. This review provides a comprehensive overview of DDIs that involve targeted therapies approved by the FDA for the treatment of solid tumours for more than 3 years (sorafenib, sunitinib, erlotinib, gefitinib, imatinib, lapatinib, everolimus, temsirolimus) and medicinal herb or drugs. This review also provides some guidelines to help oncologists and pharmacists in their clinical practice.

Contribution of ABCC4-mediated gastric transport to the absorption and efficacy of dasatinib

PURPOSE

Several oral multikinase inhibitors are known to interact in vitro with the human ATP-binding cassette transporter ABCC4 (MRP4), but the in vivo relevance of this interaction remains poorly understood. We hypothesized that host ABCC4 activity may influence the pharmacokinetic profile of dasatinib and subsequently affect its antitumor properties.

EXPERIMENTAL DESIGN

Transport of dasatinib was studied in cells transfected with human ABCC4 or the ortholog mouse transporter, Abcc4. Pharmacokinetic studies were done in wild-type and Abcc4-null mice. The influence of Abcc4 deficiency on dasatinib efficacy was evaluated in a model of Ph(+) acute lymphoblastic leukemia by injection of luciferase-positive, p185(BCR-ABL)-expressing Arf(-/-) pre-B cells.

RESULTS

Dasatinib accumulation was significantly changed in cells overexpressing ABCC4 or Abcc4 compared with control cells (P < 0.001). Deficiency of Abcc4 in vivo was associated with a 1.75-fold decrease in systemic exposure to oral dasatinib, but had no influence on the pharmacokinetics of intravenous dasatinib. Abcc4 was found to be highly expressed in the stomach, and dasatinib efflux from isolated mouse stomachs ex vivo was impaired by Abcc4 deficiency (P < 0.01), without any detectable changes in gastric pH. Abcc4-null mice receiving dasatinib had an increase in leukemic burden, based on bioluminescence imaging, and decreased overall survival compared with wild-type mice (P = 0.048).

CONCLUSIONS

This study suggests that Abcc4 in the stomach facilitates the oral absorption of dasatinib, and it possibly plays a similar role for other orally administered substrates, such as acetylsalicylic acid. This phenomenon also provides a mechanistic explanation for the malabsorption of certain drugs following gastric resection.

Interactions between oral antineoplastic agents and concomitant medication: a systematic review

INTRODUCTION

In recent years, the number of oral antitumoral agents has considerably increased. Oral administration increases the risk of interactions, because most oral anticancer drugs are taken on a daily basis. Interactions can increase exposure to antitumoral agents or cause treatment failure. Many antitumoral drugs undergo enzymatic metabolism by cytochrome P450. As some act as inducers or inhibitors of one or more isoenzymes, they can lead to decreases or increases in plasma concentrations of concomitant drugs. Hence, cytostatic drugs can act not only as victims but also as perpetrators. P-glycoprotein, an efflux transporter, can also be involved in pharmacokinetic interactions.

AREAS COVERED

A Medline search was performed to summarize the available evidence of the most clinically relevant interactions between oral chemotherapy agents and other drugs. The search covered the period from 1966 until August 2012 for each antitumoral drug using the medical subject headings 'Drug Interactions' OR 'Pharmacokinetics'. While the present review is not exhaustive, it aims to increase clinicians' awareness of potential drug-drug interactions.

EXPERT OPINION

As cancer patients are often polymedicated and treated by different physicians, the risk of drug interactions between antitumoral agents and other medications is high. More clinical interaction studies are encouraged to ensure appropriate antineoplastic pharmacokinetics in clinical practice.

Drug absorption interactions between oral targeted anticancer agents and PPIs: is pH-dependent solubility the Achilles heel of targeted therapy?

A majority of the novel orally administered, molecularly targeted anticancer therapies are weak bases that exhibit pH-dependent solubility, and suppression of gastric acidity with acid-reducing agents could impair their absorption. In addition, a majority of cancer patients frequently take acid-reducing agents to alleviate symptoms of gastroesophageal reflux disease, thereby raising the potential for a common but underappreciated drug-drug interaction (DDI) that could decrease the exposure of anticancer medication and result in subsequent failure of therapy. This article is a review of the available clinical literature describing the extent of the interaction between 15 orally administered, small-molecule targeted anticancer therapies and acid-reducing agents. The currently available clinical data suggest that the magnitude of this DDI is largest for compounds whose in vitro solubility varies over the pH range 1-4. This range represents the normal physiological gastric acidity (pH ~1) and gastric acidity while on an acid-reducing agent (pH ~4).

Concurrent use of proton pump inhibitors or H2 blockers did not adversely affect nilotinib efficacy in patients with chronic myeloid leukemia

PURPOSE

The impact of proton pump inhibitors (PPIs) and histamine H2 receptor antagonists (H2 blockers) on the efficacy of nilotinib was evaluated.

METHODS

Retrospective analyses were performed in patients with newly diagnosed Philadelphia chromosome-positive (Ph+) chronic myeloid leukemia in chronic phase (CML-CP; N = 492) and in patients with imatinib-resistant or imatinib-intolerant Ph+ CML-CP (N = 256) treated with nilotinib.

RESULTS

In the newly diagnosed population, 87 (17.7 %) and 49 (10.0 %) patients received PPIs and H2 blockers, respectively. Major molecular response at 12 months was achieved by 59 (49.6 %) patients who received at least one PPI or H2 blocker (n = 119) and 153 (41.0 %) patients who did not receive any comedication (n = 373; P = 0.13). PPIs and H2 blockers were used by 77 (30.1 %) and 17 (6.6 %) patients with imatinib-resistant or imatinib-intolerant CML-CP, respectively. Major cytogenetic response by 12 months was achieved by 55 (64.0 %) patients who received at least one PPI or H2 blocker (n = 86) versus 98 (57.6 %) patients who did not receive any comedication (n = 170; P = 0.40); 39 (45.3 %) versus 65 (38.2 %), respectively, achieved complete cytogenetic response by 12 months (P = 0.34). Similar findings were observed in patients who received comedication for >50 % of the time on nilotinib therapy. Nilotinib steady-state trough concentration was not affected by the presence of PPIs or H2 blockers.

CONCLUSIONS

Concurrent use of PPIs or H2 blockers did not affect the pharmacokinetics and efficacy of nilotinib in patients with Ph+ CML-CP.

Rationalization and prediction of in vivo metabolite exposures: the role of metabolite kinetics, clearance predictions and in vitro parameters

IMPORTANCE OF THE FIELD

Due to growing concerns over toxic or active metabolites, significant efforts have been focused on qualitative identification of potential in vivo metabolites from in vitro data. However, limited tools are available to quantitatively predict their human exposures.

AREAS COVERED IN THIS REVIEW

Theory of clearance predictions and metabolite kinetics is reviewed together with supporting experimental data. In vitro and in vivo data of known circulating metabolites and their parent drugs were collected and the predictions of in vivo exposures of the metabolites were evaluated.

WHAT THE READER WILL GAIN

The theory and data reviewed will be useful in early identification of human metabolites that will circulate at significant levels in vivo and help in designing in vivo studies that focus on characterization of metabolites. It will also assist in rationalization of metabolite-to-parent ratios used as markers of specific enzyme activity.

TAKE HOME MESSAGE

The relative importance of a metabolite in comparison to the parent compound as well as other metabolites in vivo can only be predicted using the metabolite's in vitro formation and elimination clearances, and the in vivo disposition of a metabolite can only be rationalized when the elimination pathways of that metabolite are known.

Effect of omeprazole on the pharmacokinetics and toxicities of irinotecan in cancer patients: a prospective cross-over drug-drug interaction study

BACKGROUND

Omeprazole is one of the most prescribed medications worldwide and within the class of proton pump inhibitors, it is most frequently associated with drug interactions. In vitro studies have shown that omeprazole can alter the function of metabolic enzymes and transporters that are involved in the metabolism of irinotecan, such as uridine diphosphate glucuronosyltransferase subfamily 1A1 (UGT1A1), cytochrome P-450 enzymes subfamily 3A (CYP3A) and ATP-binding cassette drug-transporter G2 (ABCG2). In this open-label cross-over study we investigated the effects of omeprazole on the pharmacokinetics and toxicities of irinotecan.

METHODS

Fourteen patients were treated with single agent irinotecan (600mg i.v., 90min) followed 3weeks later by a second cycle with concurrent use of omeprazole 40mg once daily, which was started 2weeks prior to the second cycle. Plasma samples were obtained up to 55h after infusion and analysed for irinotecan and its metabolites 7-ethyl-10-hydroxycampothecin (SN-38), SN-38-glucuronide (SN-38G), 7-ethyl-10-[4-(1-piperidino)-1-amino]-carbonyloxycamptothecin (NPC) and 7-ethyl-10-[4-N-(5-aminopentanoic acid)-1-piperidino]-carbonyloxycamptothecin (APC) by high-performance liquid chromatography (HPLC). Non-compartmental modelling was performed. Toxicities were monitored during both cycles. Paired statistical tests were performed with SPSS.

RESULTS

The exposure to irinotecan and its metabolites was not significantly different between both cycles. Neither were there significant differences in the absolute nadir and percentage decrease of WBC and ANC, nor on the incidence and severity of neutropenia, febrile neutropenia, diarrhoea, nausea and vomiting when irinotecan was combined with omeprazole.

CONCLUSION

Omeprazole 40mg did not alter the pharmacokinetics and toxicities of irinotecan. This widely used drug can, therefore, be safely administered during a 3-weekly single agent irinotecan schedule.

Drug interactions in childhood cancer

Children with cancer are increasingly benefiting from new treatment strategies and advances in supportive care, as shown by improvements in both survival and quality-of-life. However, the continuous emergence of new cancer drugs and supportive-care drugs has increased the possibility of harmful drug interactions; health-care providers need to be very cautious when combining drugs. We discuss the most common interactions between chemotherapeutic drugs and supportive-care drugs-such as anticonvulsants, antiemetics, uric-acid-lowering compounds, acid suppressants, antimicrobials, and pain-management medications in paediatric patients. We also review the interactions between chemotherapy drugs and food and herbal supplements, and provide recommendations to avoid unwanted and potentially fatal interactions in children with cancer. Because of the constant release of new drugs, health-care providers need to check the most recent references before making recommendations about drug interactions.