Gefitinib-phenytoin interaction is not correlated with the C-erythromycin breath test in healthy male volunteers

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.

Rifampin Drug-Drug-Interaction Studies: Reflections on the Nitrosamine Impurities Issue

Clinical development of new drugs may require dedicated drug-drug interaction (DDI) studies, such as to evaluate the effect of cytochrome P450 3A induction on the pharmacokinetics of investigational drugs. However, as a result of N-nitrosamine impurity findings in marketed rifampin formulations, the application of rifampin in DDI studies has been halted. This mini-review considers the root cause and impact of the nitrosamine impurity as well as alternative options for the continued conduct of DDIs.

A Prospective Study of Medication Surveillance of a Pediatric Tertiary Care Hospital in Lahore, Pakistan

PURPOSE

Several studies have shown that polypharmacy is the main cause of drug interactions, and the prevalence and the level of the severity varied with the duration of stay in the hospital, sex and race of the patients. The aims of this investigation were to identify the drug-drug interactions in hospitalized pediatric patients associated with polypharmacy, and to categorize the drug interactions in pharmacokinetic or pharmacodynamic interactions according to their level of severity.

METHODS

A cross-sectional, prospective analytical study was performed at a pediatric tertiary care hospital in Lahore, Pakistan for the duration of 4 months, which included prescription orders for 300 patients. Data were collected from patient medical files about previous and current medication history. Drug interactions were analyzed using interaction checker on Medscape and categorized according to the severity levels.

RESULTS

Out of 300 patients, the occurrence of drug interactions was found in 157 (52.3%) patients, while in 143 (47.7%), no interaction was found. Among these interactions, 50.7% were pharmacodynamic interactions, and 49.30% were pharmacokinetic interactions. Eighty-one percent of prescription orders with drug interactions contained more than three drugs, and 11.9% of interactions were severe. The majority of interactions were of amikacin-vancomycin, piroxicam-captopril and captopril-ciprofloxacin.

CONCLUSION

Most of the interactions were moderate among patients with multiple drug prescriptions. The drug interactions can be minimized by providing special patient monitoring and adequate management with prior knowledge of these drug interaction.

Pharmacokinetic properties and bioequivalence of gefitinib 250 mg in healthy Korean male subjects

Gefitinib is an anti-cancer drug used to treat non-small cell lung cancer. The objective of this study was to compare the pharmacokinetics and evaluate the bioequivalence of 2 orally administered gefitinib 250 mg tablets in healthy Korean subjects. A randomized, open-label, single-dose, crossover bioequivalence study was conducted. A total of 50 healthy male volunteers were randomized into 2 sequence groups. During each treatment, the subjects received the test or reference formulation of 250 mg gefitinib with a washout period of 21 days. The plasma samples were collected at pre-dose and up to 144 hours post-dose, and plasma drug concentrations were measured using validated liquid chromatography-tandem mass spectrometry. Pharmacokinetic parameters were calculated, and the formulations were considered as bioequivalent if the 90% confidence intervals (CIs) of the geometric mean ratios were within the bioequivalence limits of 0.8 to 1.25. Forty-one subjects completed the study and were included in the pharmacokinetic analysis. The 90% CIs of the geometric mean ratios of the test formulation to the reference formulation were 0.8115 to 0.9993 for maximum plasma concentration and 0.9119 to 1.0411 for area under the plasma concentration versus time curve from dosing to the last measurable concentration. There were no serious or unexpected adverse events during the study. In healthy Korean adult subjects, the test and reference formulations of gefitinib 250 mg had similar pharmacokinetic parameters and similar plasma concentration-time profiles. The test formulation of gefitinib met the regulatory criteria for assuming bioequivalence. Both formulations were safe and well-tolerated.

The Pharmacokinetics of Gefitinib in a Chinese Cancer Population Group: A Virtual Clinical Trials Population Study

Gefitinib, a selective inhibitor of the epidermal growth factor receptor (EGFR) tyrosine kinase, is used to treat non-small-cell lung cancer (NSCLC). Lung cancer rates are high in China and are expected to increase over the next decade. CYP 2D6 intermediate metaboliser (IM) phenotypes are more prevalent in the Chinese population compared to Caucasians; the increased risk of drug-drug interactions (DDI) with chemotherapy polypharmacy may lead to different clinical pharmacokinetics outcomes for Chinese patients. This study developed and validated a virtual Chinese cancer population for the pragmatic assessment of gefitinib DDI as a victim drug in Chinese and Caucasian cancer populations. When assessing the impact of 2D6 phenotypes on bupropion mediated CYP 2D6 DDI in Chinese cancer population, we found that AUC increased by at least 60% in extensive metabolizers (EM) and 30% in IM. As a result, fmCYP2D6 was reduced by 15% in IM in the presence of bupropion, translating into > 70% of EM subjects and > 48% of IM subjects with trough concentrations at steady state (Ctrough,ss) below the gefitinib target trough level. The PBPK model predicted that a 500 mg once daily dose in both EM and IM subjects successfully reduced the percent of subjects below the Ctrough,ss. Such changes in Ctrough,ss warrant further investigation and highlight the ability of pharmacokinetic modelling to investigate populations that may be difficult to recruit for traditional clinical studies.

Inhibition and induction of CYP enzymes in humans: an update

The cytochrome P450 (CYP) enzyme family is the most important enzyme system catalyzing the phase 1 metabolism of pharmaceuticals and other xenobiotics such as herbal remedies and toxic compounds in the environment. The inhibition and induction of CYPs are major mechanisms causing pharmacokinetic drug–drug interactions. This review presents a comprehensive update on the inhibitors and inducers of the specific CYP enzymes in humans. The focus is on the more recent human in vitro and in vivo findings since the publication of our previous review on this topic in 2008. In addition to the general presentation of inhibitory drugs and inducers of human CYP enzymes by drugs, herbal remedies, and toxic compounds, an in-depth view on tyrosine-kinase inhibitors and antiretroviral HIV medications as victims and perpetrators of drug–drug interactions is provided as examples of the current trends in the field. Also, a concise overview of the mechanisms of CYP induction is presented to aid the understanding of the induction phenomena.

Optimising Seniors' Metabolism of Medications and Avoiding Adverse Drug Events Using Data on How Metabolism by Their P450 Enzymes Varies with Ancestry and Drug-Drug and Drug-Drug-Gene Interactions

Many individuals ≥65 have multiple illnesses and polypharmacy. Primary care physicians prescribe >70% of their medications and renew specialists’ prescriptions. Seventy-five percent of all medications are metabolised by P450 cytochrome enzymes. This article provides unique detailed tables how to avoid adverse drug events and optimise prescribing based on two key databases. DrugBank is a detailed database of 13,000 medications and both the P450 and other complex pathways that metabolise them. The Flockhart Tables are detailed lists of the P450 enzymes and also include all the medications which inhibit or induce metabolism by P450 cytochrome enzymes, which can result in undertreatment, overtreatment, or potentially toxic levels. Humans have used medications for a few decades and these enzymes have not been subject to evolutionary pressure. Thus, there is enormous variation in enzymatic functioning and by ancestry. Differences for ancestry groups in genetic metabolism based on a worldwide meta-analysis are discussed and this article provides advice how to prescribe for individuals of different ancestry. Prescribing advice from two key organisations, the Dutch Pharmacogenetics Working Group and the Clinical Pharmacogenetics Implementation Consortium is summarised. Currently, detailed pharmacogenomic advice is only available in some specialist clinics in major hospitals. However, this article provides detailed pharmacogenomic advice for primary care and other physicians and also physicians working in rural and remote areas worldwide. Physicians could quickly search the tables for the medications they intend to prescribe.

Long-term safety of icotinib in patients with non-small cell lung cancer: a retrospective, real-world study

Background

Lung cancer is a global health problem with a high mortality, and the development of target therapy has led to a revolution in the treatment of lung cancer in recent years. Favorable efficacy and safety of icotinib have been demonstrated in patients with non-small cell lung cancer (NSCLC). Currently, minimal data are available to describe the long-term safety of icotinib in NSCLC patients.

Methods

We reviewed the safety data from 1,321 advanced NSCLC patients who were treated with icotinib. The primary endpoint was the long-term safety, defined as any adverse drug reactions (ADRs) occurred after 6 months of icotinib administration.

Results

Fewer ADRs were noticed over 6 month administration of icotinib than within 6 months in overall population (24.3% vs. 65.4%), and elderly patients (23.6% vs. 66.9%). The majority of ADRs were grade 1–2 in severity over 6 month exposure of icotinib in overall population as well as elderly patients. In overall population, the most common ADRs of icotinib during long-term use were rash (16.4%) and diarrhea (5.3%), while the incidences were 31.8% and 13.2% in the induction period, respectively. In elderly population, the most common ADRs of icotinib during long-term use were rash (15.7%) and diarrhea (4.7%), while the incidences were 27.8% and 14.9% in the induction period, respectively, and more inching was observed in the induction period as compared with long term use (6.3% vs. 0.3%).

Conclusions

There was an evidence of decreased frequency of icotinib-induced ADRs over time, and icotinib was well-tolerated in elderly NSCLC patients.

Comparative review of drug-drug interactions with epidermal growth factor receptor tyrosine kinase inhibitors for the treatment of non-small-cell lung cancer

The development of small-molecule tyrosine kinase inhibitors (TKIs) that target the epidermal growth factor receptor (EGFR) has revolutionized the management of non-small-cell lung cancer (NSCLC). Because these drugs are commonly used in combination with other types of medication, the risk of clinically significant drug–drug interactions (DDIs) is an important consideration, especially for patients using multiple drugs for coexisting medical conditions. Clinicians need to be aware of the potential for clinically important DDIs when considering therapeutic options for individual patients. In this article, we describe the main mechanisms underlying DDIs with the EGFR-TKIs that are currently approved for the treatment of NSCLC, and, specifically, the potential for interactions mediated via effects on gastrointestinal pH, cytochrome P450-dependent metabolism, uridine diphosphate-glucuronosyltransferase, and transporter proteins. We review evidence of such DDIs with the currently approved EGFR-TKIs (gefitinib, erlotinib, afatinib, osimertinib, and icotinib) and discuss several information sources that are available online to aid clinical decision-making. We conclude by summarizing the most clinically relevant DDIs with these EFGR-TKIs and provide recommendations for managing, minimizing, or avoiding DDIs with the different agents.

Drug-Drug Interactions, Safety, and Pharmacokinetics of EGFR Tyrosine Kinase Inhibitors for the Treatment of Non-Small Cell Lung Cancer

Inhibitors of the epidermal growth factor receptor (EGFR) are important treatment options for non-small cell lung cancer (NSCLC) patients with activating EGFR mutations. Erlotinib, gefitinib, afatinib, and osimertinib are approved for use in NSCLC patients, and several other agents are in clinical development. The objectives of this article are to review the pharmacokinetic and known drug interaction data for EGFR tyrosine kinase inhibitors (TKIs) available for use in NSCLC patients, as well as adverse events (AEs) commonly observed with EGFR-TKI treatment, and to discuss relevant management strategies. The importance of this information for patient care is explored from the perspective of advanced practitioners. Pharmacokinetic, drug-interaction, and safety data are included for EGFR inhibitors approved for NSCLC (erlotinib, gefitinib, afatinib, and osimertinib). Relevant dose modifications and AE management strategies are also reviewed. The interdisciplinary health-care team plays an essential role in patient education, care planning, and medication administration. As such, it is essential that advanced practitioners understand the safety profiles and the potential for drug interactions with EGFR TKIs to ensure patients achieve the maximum benefit from these agents.

Pharmacogenetics of drug-drug interaction and drug-drug-gene interaction: a systematic review on CYP2C9, CYP2C19 and CYP2D6

Currently, most guidelines on drug-drug interaction (DDI) neither consider the potential effect of genetic polymorphism in the strength of the interaction nor do they account for the complex interaction caused by the combination of DDI and drug-gene interaction (DGI) where there are multiple biotransformation pathways, which is referred to as drug-drug-gene interaction (DDGI). In this systematic review, we report the impact of pharmacogenetics on DDI and DDGI in which three major drug-metabolizing enzymes - CYP2C9, CYP2C19 and CYP2D6 - are central. We observed that several DDI and DDGI are highly gene-dependent, leading to a different magnitude of interaction. Precision drug therapy should take pharmacogenetics into account when drug interactions in clinical practice are expected.

Observation of hepatotoxicity during long-term gefitinib administration in patients with non-small-cell lung cancer

To observe drug-induced hepatotoxicity by long-term gefitinib administration in the treatment of non-small-cell lung cancer. The data of 101 patients with locally advanced or metastatic non-small-cell lung cancer, for which gefitinib had been used orally for 3 months or longer, were retrospectively analyzed. The median duration of gefitinib administration was 14 months (3–60 months). Forty patients (39.6%) developed abnormal hepatic function, among whom 30 patients (29.7%) had grade I hepatotoxicity, six patients (5.9%) had grade II, and four patients (4.0%) had grade III, respectively. The median time from starting gefitinib oral therapy to developing liver dysfunction was 4 months (1–23 months) for the entire cohort. The incidence of hepatotoxicity in the group with a duration of more than 14 months was much higher than that in the group with a duration of less than 14 months (52.0 vs. 27.5%, P=0.012). In thirty-two patients (32/40), abnormal liver function resolved with hepatoprotective treatment, whereas eight patients (8/40) had persistent grade I hepatotoxicity until the last follow-up. Our study showed that long-term gefitinib-induced hepatotoxicity was a common adverse event, especially for the cohort with a duration of longer than 14 months. In most patients with hepatotoxicity, normal liver function was restored and discontinuation of gefitinib was not necessary.

Effects of polymorphisms in CYP2D6 and ABC transporters and side effects induced by gefitinib on the pharmacokinetics of the gefitinib metabolite, O-desmethyl gefitinib

We investigated the effects of polymorphisms in CYP2D6, ABCB1, and ABCG2 and the side effects induced by gefitinib on the pharmacokinetics of O-desmethyl gefitinib, the active metabolite of gefitinib. On day 14 after beginning therapy with gefitinib, plasma concentrations of gefitinib and O-desmethyl gefitinib were measured. Patients were grouped into three groups according to their combination of CYP2D6 alleles: homozygous extensive metabolisers (EMs; *1/*1, *1/*2, and *2/*2; n = 13), heterozygous EMs (*1/*5, *2/*5, *1/*10, and *2/*10; n = 18), and intermediate metabolisers (IMs; *5/*10 and *10/*10; n = 5). The median AUC0-24 of O-desmethyl gefitinib in CYP2D6 IMs was 1460 ng h/mL, whereas that in homozygous EMs was 12,523 ng h/mL (P = 0.021 in univariate analysis). The median AUC ratio of O-desmethyl gefitinib to gefitinib differed among homozygous EMs, heterozygous EMs, and IMs at a ratio of 1.41:0.86:0.24 (P = 0.030). On the other hand, there were no significant differences in the AUC0-24 of O-desmethyl gefitinib between ABCB1 and ABCG2 genotypes. In a multivariate analysis, CYP2D6 homozygous EMs (P = 0.012) were predictive for a higher AUC0-24 of O-desmethyl gefitinib. The side effects of diarrhoea, skin rash, and hepatotoxicity induced by gefitinib were unrelated to the AUC0-24 of O-desmethyl gefitinib. CYP2D6 polymorphisms were associated with the formation of O-desmethyl gefitinib from gefitinib. In CYP2D6 homozygous EMs, the plasma concentrations of O-desmethyl gefitinib were higher over 24 h after taking gefitinib than those of the parent compound; however, side effects induced by gefitinib were unrelated to O-desmethyl gefitinib exposure.

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.

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.

Polymorphisms of CYP2D6 gene and gefitinib-induced hepatotoxicity

INTRODUCTION

Gefitinib induces severe hepatotoxicity in approximately a quarter of Japanese patients with epidermal growth factor receptor (EGFR) mutation-positive non-small-cell lung cancer (NSCLC). Gefitinib is metabolized by cytochrome P450 (CYP) enzymes--including CYP3A4/5, CYP1A1, and CYP2D6--in the liver. We hypothesized that polymorphisms of the CYP2D6 gene may account for gefitinib-induced hepatotoxicity.

PATIENTS AND METHODS

Polymorphisms of the CYP2D6 gene were analyzed in 55 patients with NSCLC who experienced grade ≥ 2 transaminase elevation from gefitinib. The distribution of the CYP2D6 genotype was compared with that of the healthy Japanese population. The correlations between the nonfunctional allele *5 or the reduced-function allele *10 and hepatotoxicity-related clinical factors were also examined.

RESULTS

The distribution of the CYP2D6 genotype in the study participants was not different from that of the general Japanese population, reported previously. Existence of allele *5 or *10 did not correlate with clinical factors such as onset of hepatotoxicity within 2 months, grade ≥ 3 serum transaminase elevation, and tolerability to dose reduction or rechallenge of gefitinib. However, in 7 patients taking CYP3A4-inhibitory drugs, rechallenge of gefitinib again caused hepatotoxicity in 4 patients with allele *5 or *10 but not in 3 patients with normal alleles (P = .029). Moreover, switching to erlotinib did not cause hepatotoxicity in any of 17 patients with allele *5 or *10 but did in 3 of 8 patients without these alleles (P = .024).

CONCLUSION

Reduced function of CYP2D6 may partly account for gefitinib-induced hepatotoxicity when CYP3A4 is inhibited. Erlotinib could be safely used in patients with decreased CYP2D6 activity even after they experienced gefitinib-induced hepatotoxicity.

OATP1B1 polymorphism as a determinant of erythromycin disposition

Previous studies have demonstrated that the pharmacokinetic profile of erythromycin, a probe for CYP3A4 activity, is affected by inhibitors or inducers of hepatic solute carriers. We hypothesized that these interactions are mediated by OATP1B1 (gene symbol, SLCO1B1), a polypeptide expressed on the basolateral surface of hepatocytes. Using stably transfected Flp-In T-Rex293 cells, erythromycin was found to be a substrate for OATP1B1*1A (wild type) with a Michaelis-Menten constant of ~13 µmol/l, and that its transport was reduced by ~50% in cells expressing OATP1B1*5 (V174A). Deficiency of the ortholog transporter Oatp1b2 in mice was associated with a 52% decrease in the metabolic rate of erythromycin (P = 0.000043). In line with these observations, in humans the c.521T>C variant in SLCO1B1 (rs4149056), encoding OATP1B1*5, was associated with a decline in erythromycin metabolism (P = 0.0072). These results suggest that impairment of OATP1B1 function can alter erythromycin metabolism, independent of changes in CYP3A4 activity.

Pharmacokinetic interaction between ivabradine and phenytoin in healthy subjects

BACKGROUND

Phenytoin is an inductor of the main metabolizing enzyme of ivabradine and it could influence its pharmacokinetics. Changes in ivabradine pharmacokinetics could have clinical significance regarding the safety of the treatment.

OBJECTIVE

The study objective was evaluation of the pharmacokinetic interaction between ivabradine and phenytoin in healthy subjects.

METHODS

A single dose of ivabradine 10 mg was administered alone or in combination with phenytoin 150 mg to 18 healthy subjects in a two-treatment study design, separated by 5 days in which the phenytoin alone was administered at a dose of 150 mg twice daily. Plasma concentrations of ivabradine were determined during a 12-hour period following drug administration, using a high-throughput liquid chromatography coupled with mass spectrometry analytical method. Pharmacokinetic parameters of ivabradine administered in each treatment were calculated using non-compartmental analysis and compared to determine if the differences were statistically significant.

RESULTS

In the two treatment periods, the mean ± SD peak plasma concentrations (C(max)) were 18.6 ± 8.0 ng/mL (ivabradine alone) and 6.5 ± 3.1 ng/mL (ivabradine after pre-treatment with phenytoin). The mean ± SD times taken to reach C(max) (t(max)) were 1.2 ± 0.7 h and 0.8 ± 0.6 h, respectively, and the total areas under the plasma concentration-time curve from time zero to infinity (AUC(∞)) were 62.3 ± 18.7 ng · h/mL and 19.2 ± 17.0 ng · h/mL, respectively. Statistically significant differences were observed for the C(max) and AUC(∞) of ivabradine when administered alone or with phenytoin, whereas for t(max) and the half-life the differences were non-significant.

CONCLUSION

This study showed that phenytoin has an important effect on the pharmacokinetics of ivabradine in healthy subjects, reducing its bioavailability by approximately 70%.