Severe Pustular Eruption Associated with Imatinib and Voriconazole in a Patient with Chronic Myeloid Leukemia

Clinical pharmacokinetics and drug-drug interactions of tyrosine-kinase inhibitors in chronic myeloid leukemia: A clinical perspective

In the past decade, numerous tyrosine kinase inhibitors (TKIs) have been introduced in the treatment of chronic myeloid leukemia. Given the significant interpatient variability in TKIs pharmacokinetics, potential drug-drug interactions (DDIs) can greatly impact patient therapy. This review aims to discuss the pharmacokinetic characteristics of TKIs, specifically focusing on their absorption, distribution, metabolism, and excretion profiles. Additionally, it provides a comprehensive overview of the utilization of TKIs in special populations such as the elderly, children, and patients with liver or kidney dysfunction. We also highlight known or suspected DDIs between TKIs and other drugs, highlighting various clinically relevant interactions. Moreover, specific recommendations are provided to guide haemato-oncologists, oncologists, and clinical pharmacists in managing DDIs during TKI treatment in daily clinical practice.

Overview of Drug-Drug Interactions Between Ritonavir-Boosted Nirmatrelvir (Paxlovid) and Targeted Therapy and Supportive Care for Lung Cancer

Introduction

Oral administration of ritonavir-boosted nirmatrelvir (Paxlovid) was found to be promising in the treatment of coronavirus disease 2019. The active antiviral component nirmatrelvir in Paxlovid is co-formulated with ritonavir, a strong cytochrome P450 (CYP) 3A4 inhibitor. Many oral targeted therapies indicated for lung cancer are known substrates of CYP 3A4, and concurrent use with Paxlovid may lead to potential drug-drug interaction (DDI). The purpose of this review is to evaluate the potential DDI between targeted therapies and supportive care for lung cancer and ritonavir-boosted nirmatrelvir.

Methods

Drug database search in PubMed and the Food and Drug Administration was conducted to identify pharmacokinetic data on oral tyrosine kinase inhibitors (TKIs) used in NSCLC, both Food and Drug Administration approved and those in development. Metabolism pathways for various TKIs are extracted, and the impact of TKI area under the curves and maximum concentration by strong CYP 3A4 inducers and inhibitors is summarized. The most common toxicities and supportive care medications for the TKI were identified.

Results

Among EGFR and exon 20 insertion inhibitors, afatinib is least likely to be affected by CYP 3A4, followed by dacomitinib and osimertinib. Among ALK inhibitors, alectinib is the least susceptible to CYP 3A4. ROS1 inhibitors are affected by CYP 3A4 inhibition with the exception of crizotinib. Among MET inhibitors, capmatinib is substantially affected by CYP 3A4 inhibition. Drug exposure of RET inhibitors is expected to increase with CYP 3A4 inhibition, with selpercatinib being the least affected. Certain supportive care medications for lung cancer TKI may have relevant DDIs.

Conclusions

The clinical impact of the DDI between lung cancer TKI and ritonavir-boosted nirmatrelvir varies largely on the basis of the susceptibility of CYP 3A4 inhibition caused by the antiviral. Close monitoring and medication adjustments (i.e., dose changes or alternative coronavirus disease 2019 therapy) can be used to overcome DDI to ensure patient safety.

Potentially life‑threatening severe cutaneous adverse reactions associated with tyrosine kinase inhibitors (Review)

Tyrosine kinase inhibitors (TKIs) have emerged as a new frontier of cancer therapy. These agents include inhibitors of epidermal growth factor receptor (EGFR), human epidermal growth factor receptor 2 (HER2), BRAF, mitogen‑activated protein kinase kinase (also referred to as MEK), bcr‑abl, c‑KIT, platelet‑derived growth factor (PDGFR), fibroblast growth factor receptor (FGFR), anaplastic lymphoma kinase (ALK) and vascular endothelial growth factor (VEGF). Along with the evolving applications of TKIs, there has been an increased recognition of the breadth of potential cutaneous toxicities to these agents. In this review, we provide an overview of potentially life‑threatening severe cutaneous adverse reactions (SCARs) that may occur during therapy with TKIs. These toxicities include Stevens‑Johnson Syndrome (SJS), toxic epidermal necrolysis (TEN), drug reaction with eosinophilia and systemic symptoms (DRESS), and acute generalized exanthematous pustulosis (AGEP).

Small-Molecule Protein Kinases Inhibitors and the Risk of Fungal Infections

Purpose of Review

This review discusses fungal infections associated with licenced small-molecule protein kinase inhibitors. For each major drug class, the mechanism of action and targeted pathways and the impact on host defence against fungi are described.

Recent Findings

Protein kinase inhibitors are successfully used in the treatment of malignancies and immune-mediated diseases, targeting signalling pathways for a broad spectrum of cytokines and growth-stimuli. These agents predispose to fungal infections by the suppression of integral components of the adaptive and innate immune response.

Summary

The greatest risk of fungal infections is seen with bruton tyrosine kinase inhibitors, e.g. ibrutinib. Infections are also reported with agents that target mTOR, Janus kinase and break point cluster (Bcr) gene–Abelson (Abl) tyrosine kinase (BCR-ABL). The type of fungal infection fits mechanistically with the specific pathway targeted. Infections are often disseminated and present soon after the initiation of therapy. The pharmacokinetic profile, possibility of off-target kinase inhibition, and underlying disease pathology contribute to infection risk.

Drug-drug interaction study of imatinib and voriconazole in vitro and in vivo

Background: In clinical practice, common problem polypharmacy could result in the increased risks of drug-drug interactions (DDIs). Co-administered imatinib (IMA) and voriconazole (VOR) as one treatment protocol in cancer patients with fungal infections are common.Purpose: The aim of the present study was to assess the potential DDIs associated with the concurrent use of IMA and VOR in rat liver microsomes (RLMs) and in rats.Methods and results: The concentration levels of IMA, VOR, and their metabolites N-desmethyl IMA (CGP74588) and N-oxide voriconazole (N-oxide VOR) were determined by ultra performance liquid chromatography-tandem mass spectrometry. In vitro study of RLMs, VOR inhibited the IMA metabolism with the half-maximal inhibitory concentration (IC₅₀) of 105.20 μM, while IC₅₀ for IMA against VOR was 61.30 μM. After co-administered IMA and VOR in rats, the C _max of IMA was increased significantly, while the AUC_0→t, AUC_0→∞, and C _max of CGP74588 were decreased significantly. In addition, similar results were also found that the main pharmacokinetic parameters (AUC_0→t, AUC_0→∞, MRT_0→∞, T _max, and C _max) of VOR were increased significantly, while the AUC_0→t, AUC_0→∞, and C _max of N-oxide VOR were decreased significantly. Incorporation of all the results indicated that both drugs had a inhibitory effect on each other's metabolism in vitro and in vivo.Conclusion: Thus, it is of great value to monitor the concomitant use of IMA and VOR in the clinic to reduce the risks of unexpected clinical outcomes.

The impact of azole antifungal drugs on imatinib metabolism in human liver microsomes

1. Imatinib is widely used for the treatment of hematologic malignancies. It is common that imatinib is clinically co-prescribed with azole antifungal agents since these patients are more prone to invasive antifungal infection. The present study was to investigate the effects of azole antifungal drugs, including ketoconazole, fluconazole, voriconazole, itraconazole and posaconazole on imatinib metabolism. 2. The main metabolites, 1-OH midazolam and N-desmethyl imatinib, were determined in the absence and in the presence of various levels of ketoconazole, fluconazole, voriconazole, itraconazole and posaconazole. The relevant assay was also performed to screen mechanism-based inhibitors (MBI). 3.   The inhibition ability of 1-OH midazolam formation from midazolam based on IC₅₀ values was ketoconazole (0.09 µM)>itraconazole (0.31 µM)> posaconazole (0.68 µM)>voriconazole (2.10 µM) > fluconazole (8.90 µM). Similarly, the rank order of inhibitory effects on formation of N-desmethyl imatinib from imatinib was ketoconazole (4.58 µM)>itraconazole (17.45 µM)> posaconazole (31.02 µM)> voriconazole (367.9 µM) >fluconazole (1.11 mM). Posaconazole and itraconazole displayed evidence of MBI. Additionally, imatinib was also shown as a MBI of CYP3A with IC₅₀ value of 5.40 µM against the midazolam. 4. The significant difference in IC₅₀ values of midazolam and imatinib inhibited by azole antifungal agents was observed. The role of CYP2C8 in imatinib metabolism and imatinib autoinhibits CYP3A activity may explain this difference. Our findings suggest that the azole antifungal agents might have limited impacts on imatinib exposure by CYP3A activity.

Metabolism-related pharmacokinetic drug-drug interactions with tyrosine kinase inhibitors: current understanding, challenges and recommendations

Drug-drug interactions (DDIs) occur when a patient's response to the drug is modified by administration or co-exposure to another drug. The main cytochrome P450 (CYP) enzyme, CYP3A4, is implicated in the metabolism of almost all of the tyrosine kinase inhibitors (TKIs). Therefore, there is a substantial potential for interaction between TKIs and other drugs that modulate the activity of this metabolic pathway. Cancer patients are susceptible to DDIs as they receive many medications, either for supportive care or for treatment of toxicity. Differences in DDI outcomes are generally negligible because of the wide therapeutic window of common drugs. However for anticancer agents, serious clinical consequences may occur from small changes in drug metabolism and pharmacokinetics. Therefore, the objective of this review is to highlight the current understanding of DDIs among TKIs, with a focus on metabolism, as well as to identify challenges in the prediction of DDIs and provide recommendations.

Consensus guidelines for optimising antifungal drug delivery and monitoring to avoid toxicity and improve outcomes in patients with haematological malignancy, 2014

Antifungal agents may be associated with significant toxicity or drug interactions leading to sub-therapeutic antifungal drug concentrations and poorer clinical outcomes for patients with haematological malignancy. These risks may be minimised by clinical assessment, laboratory monitoring, avoidance of particular drug combinations and dose modification. Specific measures, such as the optimal timing of oral drug administration in relation to meals, use of pre-hydration and electrolyte supplementation may also be required. Therapeutic drug monitoring (TDM) of antifungal agents is warranted, especially where non-compliance, non-linear pharmacokinetics, inadequate absorption, a narrow therapeutic window, suspected drug interaction or unexpected toxicity are encountered. Recommended indications for voriconazole and posaconazole TDM in the clinical management of haematology patients are provided. With emerging knowledge regarding the impact of pharmacogenomics upon metabolism of azole agents (particularly voriconazole), potential applications of pharmacogenomic evaluation to clinical practice are proposed.

Cutaneous adverse effects of targeted therapies: Part I: Inhibitors of the cellular membrane

There has been a rapid emergence of numerous targeted agents in the oncology community in the last decade. This exciting paradigm shift in drug development lends promise for the future of individualized medicine. Given the pace of development and clinical deployment of targeted agents with novel mechanisms of action, dermatology providers may not be familiar with the full spectrum of associated skin-related toxicities. Cutaneous adverse effects are among the most frequently observed toxicities with many targeted agents, and their intensity can be dose-limiting or lead to therapy discontinuation. In light of the often life-saving nature of emerging oncotherapeutics, it is critical that dermatologists both understand the mechanisms and recognize clinical signs and symptoms of such toxicities in order to provide effective clinical management. Part I of this continuing medical education article will review in detail the potential skin-related adverse sequelae, the frequency of occurrence, and the implications associated with on- and off-target cutaneous toxicities of inhibitors acting at the cell membrane level, chiefly inhibitors of epidermal growth factor receptor, KIT, and BCR-ABL, angiogenesis, and multikinase inhibitors.

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.

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.

Adverse skin effects of imatinib, a tyrosine kinase inhibitor

Imatinib mesylate is a tyrosine kinase inhibitor that targets the BCR-ABL, c-kit, and PDGF (platelet-derived growth factor) receptors. Imatinib is mainly indicated for chronic myeloid leukemia and gastrointestinal stromal tumors but is also prescribed by dermatologists for dermatofibrosarcoma protuberans, systemic sclerosis, and systemic mastocytosis, among other conditions. Most adverse effects are mild or moderate and therapy is generally well tolerated. Adverse skin effects are very common and include nonspecific manifestations such as edema and maculopapular rashes or eruptions of diverse types (lichenoid or psoriasiform lesions, acute generalized exanthematic pustulosis, Stevens-Johnson syndrome, and more). Identifying and properly treating these reactions can help optimize adherence to treatment and improve the prognosis of the underlying disease.

Imatinib, dasatinib and nilotinib: a review of adverse cutaneous reactions with emphasis on our clinical experience

In the last years, several tyrosine kinase inhibitors (TKIs) have been developed and approved for human cancer treatment. Imatinib mesylate was the first of this novel family of drugs that target cancer-specific molecules and signalling pathways. The appearance of imatinib resistances led to the introduction of second-generation TKIs with higher potency and selectivity, such as dasatinib and nilotinib. However, the range of activity of these agents is not simply directed at tumour cells. Patients and their clinicians are indeed frequently confronted with the cutaneous side-effects associated with the employ of these drugs, which represent the most common non-hematological adverse reactions. For this reason, a systematic dermatological survey of patients receiving these therapies is highly important, and an early and appropriate dermatological treatment is required. In this review, we analyse the clinical and pathological characteristics of the most commonly reported adverse skin events associated with first- and second-generation tyrosine kinase inhibitors, with a particular emphasis on our clinical experience.

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.

Grading dermatologic adverse events of cancer treatments: the Common Terminology Criteria for Adverse Events Version 4.0

Dermatologic adverse events to cancer therapies have become more prevalent and may to lead to dose modifications or discontinuation of life-saving or prolonging treatments. This has resulted in a new collaboration between oncologists and dermatologists, which requires accurate cataloging and grading of side effects. The Common Terminology Criteria for Adverse Events Version 4.0 is a descriptive terminology and grading system that can be used for uniform reporting of adverse events. A proper understanding of this standardized classification system is essential for dermatologists to properly communicate with all physicians caring for patients with cancer.

Adverse cutaneous reactions secondary to tyrosine kinase inhibitors including imatinib mesylate, nilotinib, and dasatinib

Imatinib mesylate is the first of a novel group of drugs that specifically target protein tyrosine kinases, which are central to the pathogenesis of human cancer. It has been approved for the treatment of chronic myeloid leukemia and gastrointestinal stromal tumor and has been found efficacious in other neoplastic diseases. Nilotinib and dasatinib, a second-generation of tyrosine kinase inhibitors (TKIs), were developed in response to findings of emerging imatinib resistance or intolerance to the drug. Cutaneous reactions are the most common nonhematologic side effect of these drugs, and their management is challenging especially in the absence of alternative anticancer agents. The present review focuses on the clinical characteristics and the hypothesized molecular pathogenesis of these first- and second-generation TKIs' cutaneous side effects, and approaches to their treatment. The wide range of adverse effects clarifies the difficulty in designing a truly antitumoral TKI.

Drug interactions with the tyrosine kinase inhibitors imatinib, dasatinib, and nilotinib

Several cancer treatments are shifting from traditional, time-limited, nonspecific cytotoxic chemotherapy cycles to continuous oral treatment with specific protein-targeted therapies. In this line, imatinib mesylate, a selective tyrosine kinases inhibitor (TKI), has excellent efficacy in the treatment of chronic myeloid leukemia. It has opened the way to the development of additional TKIs against chronic myeloid leukemia, including nilotinib and dasatinib. TKIs are prescribed for prolonged periods, often in patients with comorbidities. Therefore, they are regularly co-administered along with treatments at risk of drug-drug interactions. This aspect has been partially addressed so far, calling for a comprehensive review of the published data. We review here the available evidence and pharmacologic mechanisms of interactions between imatinib, dasatinib, and nilotinib and widely prescribed co-medications, including known inhibitors or inducers of cytochromes P450 or drug transporters. Information is mostly available for imatinib mesylate, well introduced in clinical practice. Several pharmacokinetic aspects yet remain insufficiently investigated for these drugs. Regular updates will be mandatory and so is the prospective reporting of unexpected clinical observations.

Principal long-term adverse effects of imatinib in patients with chronic myeloid leukemia in chronic phase

Imatinib mesylate (IM), an original Abl tyrosine kinase inhibitor, entered the clinics in 1998 for the treatment of patients with chronic myeloid leukemia (CML). The drug is universally considered the treatment of choice for most, if not all, patients with CML. Importantly, lessons learned from patients with CML have been applied successfully for the treatment of patients with other disorders where IM has since been found to be active by virtue of its ability to target other kinases, such as c-kit in patients with gastrointestinal stromal tumors. IM is associated with mild to moderate toxicity, mostly reversible by dose reduction or discontinuation of the drug. Most adverse effects occur within the first 2 years of starting therapy; however, late effects, many being unique, are now being recognized. In this report, we assess the toxicity associated with IM, with an emphasis on the long-term adverse effects.

Safety of triazole antifungal drugs in patients with cancer

Triazole drugs are widely used in cancer patients for prophylaxis and treatment of life-threatening invasive fungal infections. Fluconazole, available for over two decades, is safe and effective in patients with cancer; however, the excellent safety profile of fluconazole may not be applicable to the newer triazoles. Itraconazole, voriconazole and posaconazole are associated with adverse events, and drug interactions frequently occur, particularly in cancer patients, since the triazoles and many drugs used in cancer chemotherapy are metabolized via a common metabolic pathway, the hepatic cytochrome P450 system. Close monitoring for drug interactions is needed when triazoles are used with anti-neoplastic drugs and dosage modification of the triazole or its discontinuation may be required. Monitoring of triazole serum concentrations is becoming an important aspect of management to minimize toxicity and ensure efficacy.

Pneumonia caused by Candida krusei and Candida glabrata in a patient with chronic myeloid leukemia receiving imatinib mesylate treatment

In this report we describe a patient suffering from chronic myeloid leukemia (CML), who was treated for 4.5 years with imatinib and developed pneumonia caused by two Candida species, i.e., C. krusei and C. glabrata. The patient was in complete hematologic remission and molecular analyses did not display the presence of TLR2-R752Q, TLR4-D299G and TLR4-T399I polymorphisms that may predispose individuals to fungal infections. This case report indicates that in some patients, as previously observed, the long-term administration of targeted therapy might affect immunity and predispose patients to opportunistic and life-threatening fungal infections.

Imatinib metabolite profiling in parallel to imatinib quantification in plasma of treated patients using liquid chromatography-mass spectrometry

Besides affecting the systemic bioavailability of the parent drug, drug metabolizing enzymes (DMEs) may produce bioactive and/or toxic metabolites of clinical interest. We have investigated the capability to analyze simultaneously the parent drug and newly identified metabolites in patients' plasma by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). The anticancer drug, imatinib, was chosen as a model drug because it has opened a new area in cancer therapy and is given orally and chronically. In addition, resistance and rare but sometimes severe side effects have been reported with this therapy. The quantification of imatinib and the profiling of its metabolites in plasma were established following three steps: (1) set-up of a generic sample extraction and LC-MS/MS conditions, (2) metabolite identification by LC-MS/MS using either in vitro incubations performed with human liver microsomes (HLMs) or patient plasma samples, (3) the simultaneous determination of plasma levels of imatinib and 14 metabolites in the plasma samples of 38 patients. Partial or cross method validation has been done and revealed that precise determinations of metabolite levels can be performed whereas pure standards are not available. Preliminary results indicate that the disposition of imatinib and its metabolites is related to interindividual variables and that outlier metabolite profiles can be revealed. This article underscores that, in addition to usual therapeutic drug monitoring (TDM), LC-MS/MS methods can simultaneously record a complete drug metabolic profile enabling various correlation studies of clinical interest.

Relationship of imatinib-free plasma levels and target genotype with efficacy and tolerability

Imatinib has revolutionised the treatment of chronic myeloid leukaemia (CML) and gastrointestinal stromal tumours (GIST). Using a nonlinear mixed effects population model, individual estimates of pharmacokinetic parameters were derived and used to estimate imatinib exposure (area under the curve, AUC) in 58 patients. Plasma-free concentration was deduced from a model incorporating plasma levels of alpha₁-acid glycoprotein. Associations between AUC (or clearance) and response or incidence of side effects were explored by logistic regression analysis. Influence of KIT genotype was also assessed in GIST patients. Both total (in GIST) and free drug exposure (in CML and GIST) correlated with the occurrence and number of side effects (e.g. odds ratio 2.7±0.6 for a two-fold free AUC increase in GIST; P<0.001). Higher free AUC also predicted a higher probability of therapeutic response in GIST (odds ratio 2.6±1.1; P=0.026) when taking into account tumour KIT genotype (strongest association in patients harbouring exon 9 mutation or wild-type KIT, known to decrease tumour sensitivity towards imatinib). In CML, no straightforward concentration–response relationships were obtained. Our findings represent additional arguments to further evaluate the usefulness of individualising imatinib prescription based on a therapeutic drug monitoring programme, possibly associated with target genotype profiling of patients.

Chemotherapeutic agents and the skin: An update

Chemotherapeutic agents give rise to numerous well described adverse effects that may affect the skin, hair, mucous membranes, or nails. The mucocutaneous effects of longstanding agents have been extensively studied and reviewed. Over the last 2 decades, a number of new molecular entities for the treatment of cancer have been approved by the United States Food and Drug Administration (FDA). This article reviews the cutaneous toxicity patterns of these agents. It also reviews one drug that has not received FDA approval but is in use outside the United States and is important dermatologically. Particular emphasis is placed on the novel signal transduction inhibitors as well as on newer literature pertaining to previously described reactions.

LEARNING OBJECTIVES

At the completion of this learning activity, participants should able to list the newer chemotherapeutic agents that possess significant mucocutaneous side effects and describe the range of reactions that are seen with each drug. In addition, they should be able to formulate appropriate management strategies for these reactions.

Population pharmacokinetics of imatinib and the role of alpha-acid glycoprotein

AIMS

The aims of this observational study were to assess the variability in imatinib pharmacokinetics and to explore the relationship between its disposition and various biological covariates, especially plasma alpha1-acid glycoprotein concentrations.

METHODS

A population pharmacokinetic analysis was performed using NONMEM based on 321 plasma samples from 59 patients with either chronic myeloid leukaemia or gastrointestinal stromal tumours. The influence of covariates on oral clearance and volume of distribution was examined. Furthermore, the in vivo intracellular pharmacokinetics of imatinib was explored in five patients.

RESULTS

A one-compartment model with first-order absorption appropriately described the data, giving a mean (+/-SEM) oral clearance of 14.3 l h-1 (+/-1.0) and a volume of distribution of 347 l (+/-62). Oral clearance was influenced by body weight, age, sex and disease diagnosis. A large proportion of the interindividual variability (36% of clearance and 63% of volume of distribution) remained unexplained by these demographic covariates. Plasma alpha1-acid glycoprotein concentrations had a marked influence on total imatinib concentrations. Moreover, we observed an intra/extracellular ratio of 8, suggesting substantial uptake of the drug into the target cells.

CONCLUSION

Because of the high pharmacokinetic variability of imatinib and the reported relationships between its plasma concentration and efficacy and toxicity, the usefulness of therapeutic drug monitoring as an aid to optimizing therapy should be further investigated. Ideally, such an approach should take account of either circulating alpha1-acid glycoprotein concentrations or free imatinib concentrations.

Population pharmacokinetics of imatinib and the role of alpha-acid glycoprotein

AIMS

The aims of this observational study were to assess the variability in imatinib pharmacokinetics and to explore the relationship between its disposition and various biological covariates, especially plasma alpha1-acid glycoprotein concentrations.

METHODS

A population pharmacokinetic analysis was performed using NONMEM based on 321 plasma samples from 59 patients with either chronic myeloid leukaemia or gastrointestinal stromal tumours. The influence of covariates on oral clearance and volume of distribution was examined. Furthermore, the in vivo intracellular pharmacokinetics of imatinib was explored in five patients.

RESULTS

A one-compartment model with first-order absorption appropriately described the data, giving a mean (+/-SEM) oral clearance of 14.3 l h-1 (+/-1.0) and a volume of distribution of 347 l (+/-62). Oral clearance was influenced by body weight, age, sex and disease diagnosis. A large proportion of the interindividual variability (36% of clearance and 63% of volume of distribution) remained unexplained by these demographic covariates. Plasma alpha1-acid glycoprotein concentrations had a marked influence on total imatinib concentrations. Moreover, we observed an intra/extracellular ratio of 8, suggesting substantial uptake of the drug into the target cells.

CONCLUSION

Because of the high pharmacokinetic variability of imatinib and the reported relationships between its plasma concentration and efficacy and toxicity, the usefulness of therapeutic drug monitoring as an aid to optimizing therapy should be further investigated. Ideally, such an approach should take account of either circulating alpha1-acid glycoprotein concentrations or free imatinib concentrations.

Emerging Safety Issues with Imatinib and Other Abl Tyrosine Kinase Inhibitors

Imatinib and other Abl tyrosine kinase inhibitors (TKIs), such as dasatinib and nilotinib, have significantly improved the outcome of patients with chronic myeloid leukemia. Imatinib and dasatinib are currently Food and Drug Administration (FDA) approved, and nilotinib is expected to gain FDA approval soon. In addition, several other Abl TKIs are being evaluated in various clinical trials. Imatinib has also shown efficacy in the therapy of gastrointestinal stromal tumors, Philadelphia chromosome-positive acute lymphocytic leukemia and hypereosinophilic syndrome. Because of their efficacy, more patients will receive Abl TKIs for a longer period of time. Imatinib was FDA approved after a short follow-up because of its exceptional efficacy and safety profile. The most common adverse events reported included fluid retention, fatigue, diarrhea, and muscle cramps. With longer follow-up, issues related to the long-term use of imatinib have been discussed. Our aim is to review the emerging safety issues of Abl TKIs after a longer follow-up.

Drug-induced changes in P450 enzyme expression at the gene expression level: a new dimension to the analysis of drug-drug interactions

Drug-drug interactions (DDIs) caused by direct chemical inhibition of key drug-metabolizing cytochrome P450 enzymes by a co-administered drug have been well documented and well understood. However, many other well-documented DDIs cannot be so readily explained. Recent investigations into drug and other xenobiotic-mediated expression changes of P450 genes have broadened our understanding of drug metabolism and DDI. In order to gain additional information on DDI, we have integrated existing information on drugs that are substrates, inhibitors, or inducers of important drug-metabolizing P450s with new data on drug-mediated expression changes of the same set of cytochrome P450s from a large-scale microarray gene expression database of drug-treated rat tissues. Existing information on substrates and inhibitors has been updated and reorganized into drug-cytochrome P450 matrices in order to facilitate comparative analysis of new information on inducers and suppressors. When examined at the gene expression level, a total of 119 currently marketed drugs from 265 examined were found to be cytochrome P450 inducers, and 83 were found to be suppressors. The value of this new information is illustrated with a more detailed examination of the DDI between PPARalpha agonists and HMG-CoA reductase inhibitors. This paper proposes that the well-documented, but poorly understood, increase in incidence of rhabdomyolysis when a PPARalpha agonist is co-administered with a HMG-CoA reductase inhibitor is at least in part the result of PPARalpha-induced general suppression of drug metabolism enzymes in liver. The authors believe this type of information will provide insights to other poorly understood DDI questions and stimulate further laboratory and clinical investigations on xenobiotic-mediated induction and suppression of drug metabolism.