Bioequivalence, safety, and tolerability of imatinib tablets compared with capsules

Physiologically based pharmacokinetic modeling of imatinib and N-desmethyl imatinib for drug-drug interaction predictions

The first-generation tyrosine kinase inhibitor imatinib has revolutionized the development of targeted cancer therapy and remains among the frontline treatments, for example, against chronic myeloid leukemia. As a substrate of cytochrome P450 (CYP) 2C8, CYP3A4, and various transporters, imatinib is highly susceptible to drug-drug interactions (DDIs) when co-administered with corresponding perpetrator drugs. Additionally, imatinib and its main metabolite N-desmethyl imatinib (NDMI) act as inhibitors of CYP2C8, CYP2D6, and CYP3A4 affecting their own metabolism as well as the exposure of co-medications. This work presents the development of a parent-metabolite whole-body physiologically based pharmacokinetic (PBPK) model for imatinib and NDMI used for the investigation and prediction of different DDI scenarios centered around imatinib as both a victim and perpetrator drug. Model development was performed in PK-Sim® using a total of 60 plasma concentration-time profiles of imatinib and NDMI in healthy subjects and cancer patients. Metabolism of both compounds was integrated via CYP2C8 and CYP3A4, with imatinib additionally transported via P-glycoprotein. The subsequently developed DDI network demonstrated good predictive performance. DDIs involving imatinib and NDMI were simulated with perpetrator drugs rifampicin, ketoconazole, and gemfibrozil as well as victim drugs simvastatin and metoprolol. Overall, 12/12 predicted DDI area under the curve determined between first and last plasma concentration measurements (AUClast) ratios and 12/12 predicted DDI maximum plasma concentration (Cmax) ratios were within twofold of the respective observed ratios. Potential applications of the final model include model-informed drug development or the support of model-informed precision dosing.

A case-matched study of imatinib mesylate between different formulations on plasma trough concentration, adverse events, quality of life and outcomes in gastrointestinal stromal tumor patients

Genike, the imatinib (IM)-alpha form is widely used in the treatment of gastrointestinal stromal tumor (GIST) patients in China. We wanted to investigate whether there are differences in IM plasma concentrations, adverse events, health-related quality of life (QOL) and outcomes between patients treated with Genike and Glivec. Thirty included GIST patients receiving IM treatment were matched to either Genike or Glivec according to gastrectomy, body weight, body surface area and sex. There was no statistically significant difference in IM trough plasma levels between the two groups. There were no significant differences in very common adverse events of IM between the Genike and Glivec groups. IM was well tolerated, although it was associated with a significant change in cognitive function (P < 0.001), fatigue (P = 0.015), pain (P = 0.015), nausea/vomiting (P = 0.029), insomnia (P = 0.019), diarrhea (P = 0.003) and financial difficulties (P < 0.001). Physical functioning, financial burden and insomnia were significantly different between the two groups (P = 0.026). Until Aug. 2022, there was no significant difference in time to imatinib treatment failure (TTF) between the two groups. In conclusion, there was no difference in IM plasma concentration and adverse events between Genike and Glivec. Both Genike and Glivec could partially decrease the QOL of GIST patients. Physical functioning was worse in Genike group than in Glivec group, while the economic burden and symptoms of insomnia in Glivec patients were worse. There was no significant difference in TTF between the two groups.

Hemodialysis and imatinib: Plasma levels, efficacy and tolerability in a patient with metastatic GIST - Case report

Purpose

To study plasma levels, efficacy and tolerability of imatinib in a patient affected by metastatic GIST treated with oral Imatinib and undergoing hemodialysis.

Patients and methods

The patient suffered from metastatic GIST to the liver having a mutation of exon 9 of KIT. He was on hemodialysis and received first-line treatment with imatinib 400 mg/day.

Results

The overall mean plasma level of imatinib was 1875,4 ng/ml pre-dialysis, 1553,0 ng/ml post-dialysis and 1998,1 ng/ml post-24h. In red blood cells the overall mean level of imatinib was 619,5 ng/ml pre-dialysis, 484,9 ng/ml post-dialysis and 663,1 ng/ml post-24h. The plasma level of nor-imatinib/imatinib was 16,2% pre-dialysis, 15,6% post-dialysis and 16,4% post-24h. Comparing our findings regarding levels of imatinib in plasma and RBC, we found a statistically significant difference between pre-dialysis and post-dialysis (respectively p < 0,001 and p = 0,002), post-dialysis and post-24h (both p < 0,001), pre-dialysis and post-24h (respectively p = 0.035 and p = 0,042). Ultimately, regarding nor-imatinib/imatinib in plasma, we did not find any statistically significant difference between pre-dialysis and post-dialysis (p = 0,091), post-dialysis and post-24h (p = 0,091), pre-dialysis and post-24h (p = 0.903). Currently the patient is receiving oral imatinib 400 mg/day with radiological evidence of response.

Conclusion

In this case, hemodialysis did not affect significantly imatinib plasma levels. The statistically significant difference between pre- and post-dialysis can be explained by the fact that dialysis may likely contribute to a small portion of the normal metabolism of imatinib. The evaluation of imatinib levels in RBC and of its main metabolite in plasma also suggests that hemodialysis did not affect other aspects of the elimination of the drug.

Therapeutic drug monitoring of imatinib - how far are we in the leukemia setting?

INTRODUCTION

Tyrosine kinase inhibitors (TKIs) have revolutionized survival rates of chronic myeloid leukemia (CML) and Philadelphia chromosome positive (Ph+) acute lymphoblastic leukemia (ALL) and replaced hematopoietic stem cell transplantation (hSCT) as the key treatment option for these patients. More recently, the so-called Philadelphia chromosome-like (Ph-like) ALL has similarly benefitted from TKIs. However, many patients shift from the first generation TKI, imatinib, due to treatment-related toxicities or lack of treatment efficacy. A more personalized approach to TKI treatment could counteract these challenges and potentially be more cost-effective. Therapeutic drug monitoring (TDM) has led to higher response rates and less treatment-related toxicity in adult CML but is rarely used in ALL or in childhood CML.

AREAS COVERED

This review summarizes different antileukemic treatment indications for TKIs with focus on imatinib and its pharmacokinetic/-dynamic properties as well as opportunities and pitfalls of TDM for imatinib treatment in relation to pharmacogenetics and co-medication for pediatric and adult Ph+/Ph-like leukemias.

EXPERT OPINION

TDM of imatinib adds value to standard monitoring of ABL-class leukemia by uncovering non-adherence and potentially mitigating adverse effects. Clinically implementable pharmacokinetic/-dynamic models adjusted for relevant pharmacogenetics could improve individual dosing. Prospective trials of TDM-based treatments, including both children and adults, are needed.

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.

Prediction for Plasma Trough Concentration and Optimal Dosing of Imatinib under Multiple Clinical Situations Using Physiologically Based Pharmacokinetic Modeling

(1) Purpose: This study aimed to develop a physiologically based pharmacokinetic (PBPK) model to predict the trough concentration (C _trough) of imatinib (IMA) at steady state in patients and to explore the role of free concentration (f _up), α1-acid glycoprotein (AGP) level, and organic cation transporter 1 (OCT1) activity/expression in clinical efficacy. (2) Methods: The population PBPK model was built using physicochemical and biochemical properties, metabolizing and transporting kinetics, tissue distribution, and human physiological parameters. (3) Results: The PBPK model successfully predicted the C _trough of IMA administered alone in chronic phase (CP) and accelerated phase (AP) patients, the C _trough of IMA co-administered with six modulators, and C _trough in CP patients with hepatic impairment. Most of the ratios between predicted and observed data are within 0.70-1.30. Additionally, the recommendations for dosing adjustments for IMA have been given under multiple clinical uses. The sensitivity analysis showed that exploring the f _up and AGP level had a significant influence on the plasma C _trough of IMA. Meanwhile, the simulations also revealed that OCT1 activity and expression had a significant impact on the intracellular C _trough of IMA. (4) Conclusion: The current PBPK model can accurately predict the IMA C _trough and provide appropriate dosing adjustment recommendations in a variety of clinical situations.

The Application of Virtual Therapeutic Drug Monitoring to Assess the Pharmacokinetics of Imatinib in a Chinese Cancer Population Group

PURPOSE

Imatinib is used in gastrointestinal stromal tumours (GIST) and chronic myeloid leukaemia (CML). Oncology patients demonstrate altered physiology compared to healthy adults, e.g. reduced haematocrit, increased α-1 acid glycoprotein, decreased albumin and reduced glomerular filtration rate (GFR), which may influence imatinib pharmacokinetics. Given that Chinese cancer patients often report raised imatinib plasma concentrations and wider inter-individual variability reported in trough concentration when compared to Caucasian cancer patients, therapeutic drug monitoring (TDM) has been advocated.

METHOD

This study utilised a previously validated a Chinese cancer population and assessed the impact of imatinib virtual-TDM in Chinese and Caucasian cancer populations across a dosing range from 200-800 mg daily.

RESULTS

Staged dose titration to 800 mg daily, resulted in recapitulation to within the target therapeutic range for 50 % (Chinese) and 42.1% (Caucasian) subjects possessing plasma concentration < 550 ng/mL when dosed at 400 mg daily. For subjects with plasma concentrations >1500 ng/mL when dosed at 400 mg daily, a dose reduction to 200 mg once daily was able to recover 67 % (Chinese) and 87.4 % (Caucasian) patients to the target therapeutic range.

CONCLUSION

Virtual TDM highlights the benefit of pharmacokinetic modelling to optimising treatments in challenging oncology population groups.

Physiologically-based pharmacokinetic model predictions of inter-ethnic differences in imatinib pharmacokinetics and dosing regimens

AIMS

This study implements a physiologically-based pharmacokinetic (PBPK) modelling approach to investigate inter-ethnic differences in imatinib pharmacokinetics and dosing regimens.

METHODS

A PBPK model of imatinib was built in the Simcyp Simulator (version 17) integrating in vitro drug metabolism and clinical pharmacokinetic data. The model accounts for ethnic differences in body size and abundance of drug-metabolising enzymes and proteins involved in imatinib disposition. Utility of this model for prediction of imatinib pharmacokinetics was evaluated across different dosing regimens and ethnic groups. The impact of ethnicity on imatinib dosing was then assessed based on the established range of trough concentrations (C_ss,min ).

RESULTS

The PBPK model of imatinib demonstrated excellent predictive performance in describing pharmacokinetics and the attained C_ss,min in patients from different ethnic groups, shown by prediction differences that were within 1.25-fold of the clinically-reported values in published studies. PBPK simulation suggested a similar dose of imatinib (400-600 mg/d) to achieve the desirable range of C_ss,min (1000-3200 ng/mL) in populations of European, Japanese and Chinese ancestry. The simulation indicated that patients of African ancestry may benefit from a higher initial dose (600-800 mg/d) to achieve imatinib target concentrations, due to a higher apparent clearance (CL/F) of imatinib compared to other ethnic groups; however, the clinical data to support this are currently limited.

CONCLUSION

PBPK simulations highlighted a potential ethnic difference in the recommended initial dose of imatinib between populations of European and African ancestry, but not populations of Chinese and Japanese ancestry.

Inhibition of AKR1B10-mediated metabolism of daunorubicin as a novel off-target effect for the Bcr-Abl tyrosine kinase inhibitor dasatinib

Bcr-Abl tyrosine kinase inhibitors significantly improved Philadelphia chromosome-positive leukaemia therapy. Apart from Bcr-Abl kinase, imatinib, dasatinib, nilotinib, bosutinib and ponatinib are known to have additional off-target effects that might contribute to their antitumoural activities. In our study, we identified aldo-keto reductase 1B10 (AKR1B10) as a novel target for dasatinib. The enzyme AKR1B10 is upregulated in several cancers and influences the metabolism of chemotherapy drugs, including anthracyclines. AKR1B10 reduces anthracyclines to alcohol metabolites that show less antineoplastic properties and tend to accumulate in cardiac tissue. In our experiments, clinically achievable concentrations of dasatinib selectively inhibited AKR1B10 both in experiments with recombinant enzyme (Ki = 0.6 µM) and in a cellular model (IC₅₀ = 0.5 µM). Subsequently, the ability of dasatinib to attenuate AKR1B10-mediated daunorubicin (Daun) resistance was determined in AKR1B10-overexpressing cells. We have demonstrated that dasatinib can synergize with Daun in human cancer cells and enhance its therapeutic effectiveness. Taken together, our results provide new information on how dasatinib may act beyond targeting Bcr-Abl kinase, which may help to design new chemotherapy regimens, including those with anthracyclines.

Factors Influencing the Steady-State Plasma Concentration of Imatinib Mesylate in Patients With Gastrointestinal Stromal Tumors and Chronic Myeloid Leukemia

Imatinib mesylate (IM) is the standard treatment for advanced, metastatic gastrointestinal stromal tumors (GISTs) and chronic myeloid leukemia (CML) with a fixed daily standard dosage via the oral route. Interindividual and intraindividual variability in plasma concentrations have been closely linked to the efficacy of IM therapy. Therefore, this review identifies and describes the key factors influencing the plasma concentration of IM in patients with GISTs and CML. We used the following keywords to search the PubMed, EMBASE, Ovid, Wangfang, and CNKI databases to identify published reports: IM, plasma concentration, GISTs, CML, drug combination/interaction, pathology, and genotype/genetic polymorphism, either alone or in combination. This literature review revealed that only 10 countries have reported the mean concentrations of IM in GISTs or CML patients and the clinical outcomes in different ethnic groups and populations. There were totally 24 different gene polymorphisms, which were examined for any potential influence on the steady-state plasma concentration of IM. As a result, some genotype locus made discrepant conclusion. Herein, the more sample capacity, multicenter, long-term study was worthy to carry out. Eleven reports were enumerated on clinical drug interactions with IM, while there is not sufficient information on the pharmacokinetic parameters altered by drug combinations with IM that could help in investigating the actual drug interactions. The drug interaction with IM should be paid more attention in the future research.

Prednisolone or hydrocortisone replacement in patients with corticotrope deficiency fasting during Ramadan result in similar risks of complications and quality of life: a randomized double-blind controlled trial

PURPOSE

The aims of the study were to compare the risk of complications and the quality of life in patients with corticotrope deficiency, who fasted during Ramadan. Both hydrocortisone and prednisolone were compared as treatments.

METHODS

A randomized double-blind crossover clinical trial conducted in the department of Endocrinology of the University Hospital la Rabta in Tunis, during Ramadan 2018, on 53 patients with known corticotrope deficiency treated with hydrocortisone 20 mg per day and who were willing to fast during Ramadan. Patients were randomized into two groups; AB that received hydrocortisone twice daily for 14 days then prednisolone once daily with a placebo for 14 days and group BA that received the two treatments in the reverse order. Patients had to complete a daily follow-up sheet about their eating and sleeping habits, the occurrence of complications and blood glucose monitoring and also to respond to the AddiQoL questionnaire at the end of each treatment period.

RESULTS

Fifty patients' data were analyzed; 29 men, mean age: 42.4 ± 13.3 years, mean duration of the disease: 8.1 ± 7.6 years. The frequency of complications, mean blood glucose levels and the quality of life did not differ on hydrocortisone compared to prednisolone after adjustment for the sequence of the treatment.

CONCLUSIONS

the risks of Ramadan fasting in patients with corticotrope deficiency were the same on hydrocortisone or prednisolone.

A Multi-centric Bioequivalence Trial in Ph+ Chronic Myeloid Leukemia Patients to Assess Bioequivalence and Safety Evaluation of Generic Imatinib Mesylate 400 mg Tablets

PURPOSE

This study was designed to characterize the pharmacokinetic profile and to assess bioequivalence of the sponsor's test formulation (imatinib mesylate 400 mg tablets) with an innovator product (Gleevec 400 mg tablets, Novartis Pharmaceuticals) under fed conditions, in adult patients of Philadelphia chromosome positive chronic myeloid leukemia (Ph+ CML) stabilized on imatinib mesylate 400 mg. In addition, the aim of this study was to monitor the safety profile of investigational medicinal products (IMPs).

MATERIALS AND METHODS

A multicenter, randomized, open label, two-period, crossover, single dose bioequivalence study was designed for conduct under fed conditions in 42 adult Ph+ CML patients already stabilized on imatinib 400 mg tablets. Pharmacokinetic parameters Tmax, Cmax, and AUC0-24 were calculated using a non-compartmental model on validated WinNonlin software. Validated SAS software was used for statistical evaluation of data. The safety profile of investigational products was monitored during the course of study by applying a clinical process for recording observed untoward effects postadministration of investigational products.

RESULTS

The 90% confidence intervals for the test/reference mean ratios of the ln-transformed PK variables Cmax (99.0%) and AUC0-24 (99.2%) were within an acceptable range of 80%-125%, as per bioequivalence assumptions. Both formulations were well tolerated after oral administration of IMPs.

CONCLUSION

The test product was found to be bioequivalent and safe, and thus can be used interchangeably in clinical practice.

Clinical development of imatinib: an anticancer drug

BACKGROUND

A novel and accurate high-throughput tandem mass spectroscopic method has been developed and validated for determination of imatinib, a protein-tyrosine kinase inhibitor against chronic myeloid leukemia.

MATERIALS & METHODS

Chromatographic separation was carried on XTerra® RP18 column (150 mm × 4.6 mm, 5 µm particle size) manufactured by Waters Corporation, MA, USA. The detection was performed on a triple quadruple tandem mass spectrometer by multiple reactions monitoring mode via electrospray ionization source.

RESULTS

The selective and sensitive method was linear in the concentration range of 9.57-4513.29 ng/ml and reported no matrix effect.

CONCLUSION

The mean Cmax was found to be 10-15% lower in European subjects as compared with Indian subjects.

Paradoxical and contradictory effects of imatinib in two cell line models of hormone-refractory prostate cancer

BACKGROUND

Imatinib mesylate is a chemotherapeutic drug that inhibits the tyrosine kinase activity of c-KIT and has been successfully used to treat leukemias and some solid tumors. However, its application for treatment of hormone-refractory prostate cancer (HRPC) has shown modest effectiveness and did not follow the outcomes in cultured cells or animal models. Moreover, the molecular pathways by which imatinib induces cytotoxicity in prostate cancer cells are poorly characterized.

METHODS

Two cell line models of HRPC (DU145 and PC3) were exposed to 20 μM of imatinib for 6-72 hr. MTS assay was used to assess cell viability during the course of experiment. Gene expression analysis of c-KIT, cell-cycle and apoptosis regulators, and angiogenic factors was determined by means of real-time PCR, western blot, and/or immunocytochemistry. The enzymatic activity of the apoptosis effector, caspase-3, was determined by a colorimetric assay.

RESULTS

Imatinib significantly decreased the viability of DU145 cells but paradoxically augmented the viability of PC3 cells. DU145 cells displayed diminished expression of anti-apoptotic Bcl-2 protein and augmented levels of caspase-8 and -9, as well as, increased enzymatic activity of caspase-3 in response to imatinib. No differences existed on the expression levels of apoptosis-related proteins in PC3 cells treated with imatinib, though the activity of caspase-3 was decreased. The mRNA levels of angiogenic factor VEGF were decreased in DU145-treated cells, whereas an opposite effect was seen in PC3. In addition, it was shown that DU145 and PC3 cells present a differential expression of c-KIT protein variants.

CONCLUSION

DU145 and PC3 cells displayed a contradictory behavior in response to imatinib, which was underpinned by a distinct expression pattern (or activity) of target regulators of cell-cycle, apoptosis, and angiogenesis. The paradoxical effect of imatinib in PC3 cells may be related with the differential expression of c-KIT protein variants. Moreover, the present findings helped to understand the discrepancies in the efficacy of imatinib as therapeutic option in HRPC.

Tyrosine kinase inhibitors enhance ciprofloxacin-induced phototoxicity by inhibiting ABCG2

The tyrosine kinase inhibitor (TKI) class of anticancer agents inhibits ABCG2-mediated drug efflux. ABCG2 is an important component of the blood-retinal barrier, where it limits retinal exposure to phototoxic compounds such as fluoroquinolone antibiotics. Patients treated with TKIs would be expected to be at greater risk for retinal phototoxicity. Using an in vitro system, our results indicate that the TKIs gefitinib and imatinib abrogate the ability of ABCG2 to protect cells against ciprofloxacin-induced phototoxicity. We conclude that the concurrent administration of ABCG2 inhibitors with photoreactive fluoroquinolone antibiotics may result in retinal damage.

A long-term prospective population pharmacokinetic study on imatinib plasma concentrations in GIST patients

PURPOSE

Imatinib minimal (trough) plasma concentrations after one month of treatment have shown a significant association with clinical benefit in patients with gastrointestinal stromal tumors (GIST). Considering that a retrospective pharmacokinetic analysis has also suggested that imatinib clearance increases over time in patients with soft tissue sarcoma and GIST, the primary aim of this study was to assess systemic exposure to imatinib at multiple time points in a long-term prospective population pharmacokinetic study. As imatinib is mainly metabolized in the liver, our secondary aim was to elucidate the potential effects of the volume of liver metastases on exposure to imatinib.

EXPERIMENTAL DESIGN

Full pharmacokinetic blood sampling was conducted in 50 patients with GIST on the first day of imatinib treatment, and after one, six, and 12 months. In addition, on day 14, and monthly during imatinib treatment, trough samples were taken. Pharmacokinetic analysis was conducted using a compartmental model. Volume of liver metastases was assessed by computed tomographic (CT) imaging.

RESULTS

After 90 days of treatment, a significant decrease in imatinib systemic exposure of 29.3% compared with baseline was observed (P < 0.01). For every 100 cm(3) increase of metastatic volume, a predicted decrease of 3.8% in imatinib clearance was observed.

CONCLUSIONS

This is the first prospective pharmacokinetic study in patients with GIST, showing a significant decrease of approximately 30% in imatinib exposure after long-term treatment. This means that future "trough level - clinical benefit" analyses should be time point specific. GIST liver involvement, however, has a marginal effect on imatinib clearance.

A hemodialysis patient with primary extra-gastrointestinal stromal tumor: favorable outcome with imatinib mesylate

Extra-gastrointestinal stromal tumors (EGISTs) are rare. We describe a 69-year-old man with a 9-year history of hemodialysis. This patient was diagnosed as having peritoneal tumors measuring over 10 cm in length. Histologically, the tumors were composed of monomorphic spindle cells. The number of mitotic figures was 5 per 50 high-power fields. Immunohistochemical analysis revealed strong positivity for c-KIT and MIB-1. He was treated with imatinib mesylate with no recurrences 20 months later. We present this first case of EGIST in a hemodialysis patient in which imatinib mesylate had a favorable outcome and also discuss the rarity of this case.

Interchangeability of two 500 mg amoxicillin capsules with one 1000 mg amoxicillin tablet after a single oral administration

The aim of the study was to evaluate if two capsules (Amoxil^® capsules, 500 mg/capsule) and one tablet (Amoxicare^® tablets, 1000 mg/tablet) of amoxicillin have similar bioequivalence parameters. For this purpose a randomized, two-way, crossover, bioequivalence study was performed in 24 healthy, male volunteers, divided into two groups of 12 subjects each. One group was treated with the reference standard (Amoxil^®) and the other one with the generic tablet Amoxicare^®, with a crossover after a wash-out period of 7 days. Blood samples were collected at fixed time intervals and amoxicillin was determined by a validated HPLC method. The pharmacokinetic parameters AUC_0-8, AUC_0-∞, C_max, T_max, K_e and T_1/2 were determined for both formulations and statistically compared to evaluate the bioequivalence between the two brands of amoxicillin, using the statistical model recommended by the FDA. C_max and AUC_0-∞ were statistically analyzed using analysis of variance (ANOVA); no statistically significant difference was observed between the two formulations. The 90% confidence intervals between the mean values of C_max and AUC_0-∞ fall within the FDA specified bioequivalent limits (80-125%) suggesting that the two products are bioequivalent and the two formulations are interchangeable. Based on these findings it was concluded that the practice of interchangeability between the above formulations to achieve better patient compliance could be followed without compromising the extent of amoxicillin absorption.

Reduced exposure of imatinib after coadministration with acetaminophen in mice

Purpose:

Imatinib is an efficacious drug against chronic myeloid leukemia (CML) and gastrointestinal stromal tumor (GIST) due to selective inhibition of c-KIT and BCR-ABL kinases. It presents almost complete bioavailability, is eliminated via P450-mediated metabolism and is well tolerated. However, a few severe drug-drug interactions have been reported in cancer patients taking acetaminophen.

Materials and Methods:

Male ICR mice were given 100 mg/kg single dose of imatinib orally or imatinib 100 mg/kg (orally) coadministered with acetaminophen intraperitoneally (700 mg/kg). Mice were euthanized at predetermined time points, blood samples collected, and imatinib plasma concentration measured by HPLC.

Results:

Imatinib AUC_0-12 was 27.04 ± 0.38 mg·h/ml, C_max was 7.21 ± 0.99 mg/ml and elimination half-life was 2.3 hours. Acetaminophen affected the imatinib disposition profile: AUC_0-12 and C_max decreased 56% and 59%, respectively and a longer half-life was observed (5.6 hours).

Conclusions:

The study shows a pharmacokinetic interaction between acetaminophen and imatinib which may render further human studies necessary if both drugs are administered concurrently to cancer patients.

Clinical pharmacokinetics of tyrosine kinase inhibitors

In the recent years, eight tyrosine kinase inhibitors (TKIs) have been approved for cancer treatment and numerous are under investigation. These drugs are rationally designed to target specific tyrosine kinases that are mutated and/or over-expressed in cancer tissues. Post marketing study commitments have been made upon (accelerated) approval such as additional pharmacokinetic studies in patients with renal- or hepatic impairment, in children, additional interactions studies and studies on the relative or absolute bioavailability. Therefore, much information will emerge on the pharmacokinetic behavior of these drugs after their approval. In the present manuscript, the pharmacokinetic characteristics; absorption, distribution, metabolism and excretion (ADME), of the available TKIs are reviewed. Results from additional studies on the effect of drug transporters and drug-drug interactions have been incorporated. Overall, the TKIs reach their maximum plasma levels relatively fast; have an unknown absolute bioavailability, are extensively distributed and highly protein bound. The drugs are primarily metabolized by cytochrome P450 (CYP) 3A4 with other CYP-enzymes playing a secondary role. They are predominantly excreted with the feces and only a minor fraction is eliminated with the urine. All TKIs appear to be transported by the efflux ATP binding-cassette transports B1 and G2. Additionally these drugs can inhibit some of their own metabolizing enzymes and transporters making steady-state metabolism and drug-drug interactions both complex and unpredictable. By understanding the pharmacokinetic profile of these drugs and their similarities, factors that influence drug exposure will be better recognized and this knowledge may be used to limit sub- or supra-therapeutic drug exposure.

Differential effects of imatinib mesylate against uveal melanoma in vitro and in vivo

Uveal melanoma is refractory to chemotherapy. The receptor tyrosine kinase inhibitor, imatinib mesylate, has demonstrated antiproliferative effects against uveal melanoma cells in vitro. The effects of imatinib mesylate, alone and combined with the alklyating agent, temozolomide, were examined in vivo as well as in vitro. Proliferation and angiogenic factor production of human uveal melanoma cell lines in response to imatinib mesylate and temozolomide were examined in vitro. Tumor growth, angiogenic factor production, tumor interstitial fluid pressure, and stroma constituents in response to imatinib mesylate and temozolomide were examined in vivo in mice bearing human uveal melanoma xenografts. Imatinib mesylate in vitro antagonized the antiproliferative effects of temozolomide and increased the production of angiogenic factors. In contrast, pretreatment with imatinib mesylate in vivo could improve the antitumor activity of temozolomide. Imatinib mesylate in vivo decreased the production of angiogenic factors in the tumor stroma and tumor interstitial fluid pressure. These effects were transient. Increases in angiogenic factors, interstitial fluid pressure, and tumor infiltrating macrophages were observed with continued imatinib mesylate treatment in vivo. The antitumor effects of imatinib mesylate can vary in vivo when compared with in vitro. Imatinib mesylate can both positively and negatively modify host-tumor interactions in uveal melanoma.

Imatinib for hepatocellular cancer--focus on pharmacokinetic/pharmacodynamic modelling and liver function

The effects of imatinib are partly mediated by the inhibition of platelet-derived growth factor (PDGF), which is highly expressed in the liver. In this phase-I/II trial pharmacokinetic parameters of imatinib given for hepatocellular cancer were similar to those previously derived from CML patients. The AUC of N-desmethyl-imatinib depended on liver function; the metabolism of imatinib was otherwise comparable to other populations. During short-termed imatinib treatment (4 weeks, 400 mg/d), plasma PDGF significantly decreased. The AUC of N-desmethyl-imatinib could best be attributed to the pharmacodynamic effect of PDGF inhibition (r=-0.679 [95% CI: -0.917 to -0.0868], p=0.031).

Pharmacokinetic investigation of imatinib using accelerator mass spectrometry in patients with chronic myeloid leukemia

PURPOSE

To investigate the potential use of accelerator mass spectrometry (AMS) in the study of the clinical pharmacology of imatinib.

EXPERIMENTAL DESIGN

Six patients who were receiving imatinib (400 mg/d) as part of their ongoing treatment for chronic myeloid leukemia (CML) received a dose containing a trace quantity (13.6 kBq) of (14)C-imatinib. Blood samples were collected from patients before and at various times up to 72 h after administration of the test dose and were processed to provide samples of plasma and peripheral blood lymphocytes (PBL). Samples were analyzed by AMS, with chromatographic separation of parent compound from metabolites. In addition, plasma samples were analyzed by liquid chromatography/mass spectrometry (LCMS).

RESULTS

Analysis of the AMS data indicated that imatinib was rapidly absorbed and could be detected in plasma up to 72 h after administration. Imatinib was also detectable in PBL at 24 h after administration of the (14)C-labeled dose. Comparison of plasma concentrations determined by AMS with those derived by LCMS analysis gave similar average estimates of area under plasma concentration time curve (26 +/- 3 versus 27 +/- 11 microg/mL.h), but with some variation within each individual.

CONCLUSIONS

Using this technique, data were obtained in a small number of patients on the pharmacokinetics of a single dose of imatinib in the context of chronic dosing, which could shed light on possible pharmacologic causes of resistance to imatinib in CML.

The effect of imatinib mesylate (Glivec) on human tumor-derived cells

Imatinib mesylate is a specific inhibitor of the Bcr-Abl protein tyrosine kinase that competes with ATP for its specific binding site in the kinase domain. It has activity against platelet-derived growth factor receptor alpha and beta (PDGFR-alpha and -beta), and c-kit, the receptor for stem cell factor. We have used a standardized ATP-tumor chemosensitivity assay and immunohistochemistry to determine the cytotoxicity of imatinib mesylate in tumor-derived cells from cutaneous and uveal melanoma, and ovarian carcinoma. Imatinib mesylate was tested at concentrations ranging from 2.0 to 0.0625 micromol/l alone and in combination with a cytotoxic drug (cisplatin, doxorubicin, paclitaxel or treosulfan). Imatinib mesylate showed low inhibition (IndexSUM>300) across the range of concentrations tested in this study, with few tumors exhibiting increasing inhibition with increased drug concentration. The median IC90 values for cutaneous and uveal melanoma and ovarian carcinoma were 13.2 micromol/l (4.0-294.3 micromol/l), 12.0 micromol/l (2.0-285.4 micromol/l) and 7.71 micromol/l (6.51-11.02 micromol/l), respectively. Imatinib mesylate potentiated the effect of different cytotoxics in 9% (5/54) of cases and had a negative effect in 13% (7/54) of cases, with no effect in the remainder. No correlation of effect was noted with c-kit, platelet-derived growth factor receptor-alpha or platelet-derived growth factor receptor-beta expression, assessed by immunohistochemistry. The signaling pathways mediated by activation of c-kit or platelet-derived growth factor receptor may act as antiapoptotic survival signals in some cancers and inhibition of these pathways may potentiate the activity of some cytotoxic drugs by inhibiting the survival signal. Growth inhibition, however, may reduce the efficacy of cytotoxic drugs, which tend to target proliferating cells preferentially, and clinical effects are therefore difficult to predict.

Clinical pharmacokinetics of imatinib

Imatinib is a potent and selective inhibitor of the protein tyrosine kinase Bcr-Abl, platelet-derived growth factor receptors (PDGFRalpha and PDGFRbeta) and KIT. Imatinib is approved for the treatment of chronic myeloid leukaemia (CML) and gastrointestinal stromal tumour (GIST), which have dysregulated activity of an imatinib-sensitive kinase as the underlying pathogenetic feature. Pharmacokinetic studies of imatinib in healthy volunteers and patients with CML, GIST and other cancers show that orally administered imatinib is well absorbed, and has an absolute bioavailability of 98% irrespective of oral dosage form (solution, capsule, tablet) or dosage strength (100 mg, 400 mg). Food has no relevant impact on the rate or extent of bioavailability. The terminal elimination half-life is approximately 18 hours. Imatinib plasma concentrations predictably increase by 2- to 3-fold when reaching steady state with 400mg once-daily administration, to 2.6 +/- 0.8 microg/mL at peak and 1.2 +/- 0.8 microg/mL at trough, exceeding the 0.5 microg/mL (1 micromol/L) concentrations needed for tyrosine kinase inhibition in vitro and leading to normalisation of haematological parameters in the large majority of patients with CML irrespective of baseline white blood cell count. Imatinib is approximately 95% bound to human plasma proteins, mainly albumin and alpha1-acid glycoprotein. The drug is eliminated predominantly via the bile in the form of metabolites, one of which (CGP 74588) shows comparable pharmacological activity to the parent drug. The faecal to urinary excretion ratio is approximately 5:1. Imatinib is metabolised mainly by the cytochrome P450 (CYP) 3A4 or CYP3A5 and can competitively inhibit the metabolism of drugs that are CYP3A4 or CYP3A5 substrates. Interactions may occur between imatinib and inhibitors or inducers of these enzymes, leading to changes in the plasma concentration of imatinib as well as coadministered drugs. Hepatic and renal dysfunction, and the presence of liver metastases, may result in more variable and increased exposure to the drug, although typically not necessitating dosage adjustment. Age (range 18-70 years), race, sex and bodyweight do not appreciably impact the pharmacokinetics of imatinib.

Metabolism and disposition of imatinib mesylate in healthy volunteers

Imatinib mesylate (GLEEVEC, GLIVEC, formerly STI571) has demonstrated unprecedented efficacy as first-line therapy for treatment for all phases of chronic myelogenous leukemia and metastatic and unresectable malignant gastrointestinal stromal tumors. Disposition and biotransformation of imatinib were studied in four male healthy volunteers after a single oral dose of 239 mg of (14)C-labeled imatinib mesylate. Biological fluids were analyzed for total radioactivity, imatinib, and its main metabolite CGP74588. Metabolite patterns were determined by radio-high-performance liquid chromatography with off-line microplate solid scintillation counting and characterized by liquid chromatography-mass spectrometry. Imatinib treatment was well tolerated without serious adverse events. Absorption was rapid (t(max) 1-2 h) and complete with imatinib as the major radioactive compound in plasma. Maximum plasma concentrations were 0.921 +/- 0.095 mug/ml (mean +/- S.D., n = 4) for imatinib and 0.115 +/- 0.026 mug/ml for the pharmacologically active N-desmethyl metabolite (CGP74588). Mean plasma terminal elimination half-lives were 13.5 +/- 0.9 h for imatinib, 20.6 +/- 1.7 h for CGP74588, and 57.3 +/- 12.5 h for (14)C radioactivity. Imatinib was predominantly cleared through oxidative metabolism. Approximately 65 and 9% of total systemic exposure [AUC(0-24 h) (area under the concentration time curve) of radioactivity] corresponded to imatinib and CGP74588, respectively. The remaining proportion corresponded mainly to oxidized derivatives of imatinib and CGP74588. Imatinib and its metabolites were excreted predominantly via the biliary-fecal route. Excretion of radioactivity was slow with a mean radiocarbon recovery of 80% within 7 days (67% in feces, 13% in urine). Approximately 28 and 13% of the dose in the excreta corresponded to imatinib and CGP74588, respectively.

Pharmacokinetics of imatinib mesylate in end stage renal disease. A case study

AIM

To evaluate the pharmacokinetics of imatinib mesylate (Glivec) and its main metabolite (CGP74588) in a patient with end stage renal disease on hemodialysis and compare it with published data from subjects with normal renal function.

PATIENTS AND METHODS

Serial blood samples were collected over a 2-weeks period in a patient who was receiving daily 400 mg oral imatinib mesylate for the treatment of a gastrointestinal stromal tumor metastatic to the liver while on hemodialysis. Plasma levels of imatinib and CGP74588 were determined by a liquid chromatography-tandem mass spectrometry assay.

RESULTS

The pharmacokinetic values for imatinib and CGP74588, respectively, were: maximum concentration (3,340 and 781 ng/ml), time to maximum concentration (2 h), half-life (18.2 and 34.0 h), area under the curve (53.9 and 14.8 microg.h/ml), and trough concentration (1,540 and 508 ng/ml) for at least 24 h. All obtained values fell within the range of values of imatinib and its metabolite obtained in patients with normal renal function. Dialysis courses were not found to intervene with plasma kinetics of the study drug.

CONCLUSIONS

Our results indicate that the pharmacokinetics of imatinib and its metabolite CGP74588 do not change in patients with end stage renal disease on hemodialysis. Thus, the standard dose of imatinib can be safely administered to patients on hemodialysis, and probably with renal failure, at any stage.