Idiosyncratic Adverse Drug Reactions Research Articles

Use of Structural Alerts for Reactive Metabolites in the Application SpotRM.

Reactive metabolite (RM) formation is widely accepted as playing a crucial role in causing idiosyncratic adverse drug reactions (IADRs), where the liver is most affected. An important goal of drug design is to avoid selection of drug candidates giving rise to RMs and therefore risk causing problems later on involving IADRs. The simplest, initial approach is to avoid test structures that have substructures known or strongly suspected to be associated with IADRs. However, as is evident from the many case reports of IADRs, in most cases a clear association with any (bio)chemical mechanism is lacking, which makes it hard to establish any structure-toxicity relationship. Separate studies of RM formation, in vitro and in vivo, have led to likely evidence and to establishing many structural alerts (SAs) that can be used for fast selection/deselection of planned test compounds. As a background to a discussion of the concept, 25 kinase inhibitor drugs with known problems of hepatotoxicity were probed against a set of SAs contained in the application SpotRM. A clear majority of the probed drugs show liabilities as evident by being flagged by more than one of the fairly established types of SAs. At the same time, no clear SAs were found in three drugs, which is discussed in the broader context of usefulness and selection tactics of SAs in drug design.

Advancing Adverse Drug Reaction Prediction with Deep Chemical Language Model for Drug Safety Evaluation.

The accurate prediction of adverse drug reactions (ADRs) is essential for comprehensive drug safety evaluation. Pre-trained deep chemical language models have emerged as powerful tools capable of automatically learning molecular structural features from large-scale datasets, showing promising capabilities for the downstream prediction of molecular properties. However, the performance of pre-trained chemical language models in predicting ADRs, especially idiosyncratic ADRs induced by marketed drugs, remains largely unexplored. In this study, we propose MoLFormer-XL, a pre-trained model for encoding molecular features from canonical SMILES, in conjunction with a CNN-based model to predict drug-induced QT interval prolongation (DIQT), drug-induced teratogenicity (DIT), and drug-induced rhabdomyolysis (DIR). Our results demonstrate that the proposed model outperforms conventional models applied in previous studies for predicting DIQT, DIT, and DIR. Notably, an analysis of the learned linear attention maps highlights amines, alcohol, ethers, and aromatic halogen compounds as strongly associated with the three types of ADRs. These findings hold promise for enhancing drug discovery pipelines and reducing the drug attrition rate due to safety concerns.

De-risking idiosyncratic adverse drug reactions and toxicities in drug discovery utilizing a qualitative in-vitro high-throughput reactive metabolite trapping method

De-risking idiosyncratic adverse drug reactions and toxicities in drug discovery utilizing a qualitative in-vitro high-throughput reactive metabolite trapping method

Relevance of Pharmacogenomics to the Safe Use of Antimicrobials.

There has been widespread implementation of pharmacogenomic testing to inform drug prescribing in medical specialties such as oncology and cardiology. Progress in using pharmacogenomic tests when prescribing antimicrobials has been more limited, though a relatively large number of pharmacogenomic studies on aspects such as idiosyncratic adverse drug reactions have now been performed for this drug class. Currently, there are recommendations in place from either National Regulatory Agencies and/or specialist Pharmacogenomics Advisory Groups concerning genotyping for specific variants in MT-RNR1 and CYP2C19 before prescribing aminoglycosides and voriconazole, respectively. Numerous additional pharmacogenomic associations have been reported concerning antimicrobial-related idiosyncratic adverse drug reactions, particularly involving specific HLA alleles, but, to date, the cost-effectiveness of genotyping prior to prescription has not been confirmed. Polygenic risk score determination has been investigated to a more limited extent but currently suffers from important limitations. Despite limited progress to date, the future widespread adoption of preemptive genotyping and genome sequencing may provide pharmacogenomic data to prescribers that can be used to inform prescribing and increase the safe use of antimicrobials.

Piperazine ring toxicity in three novel anti-breast cancer drugs: an in silico and in vitro metabolic bioactivation approach using olaparib as a case study.

The metabolic activation of small-molecule drugs into electrophilic reactive metabolites is widely recognized as an indicator of idiosyncratic adverse drug reactions (IADRs). Three novel anti-breast cancer drugs containing piperazine rings, ribociclib (Kisqali®, RCB), abemaciclib (Verzenio®, ABC), and olaparib (Lynparza®, OLP), were selected to study the effect of different chemical environment on the piperazine ring activation using in silico and in vitro metabolic experiments. ABC and RCB were previously studied and we noticed the piperazine ring in ABC could be strongly bioactivated generating more reactive intermediates than piperazine ring in RCB. OLP was further used as a case study to show the power of in silico software to predict the piperazine ring activation that was approved using in vitro experiments. Initially, predictions of susceptible sites in the metabolism and reactivity pathways were performed using the StarDrop P450 model and XenoSite reactivity tool, respectively. Later, in vitro OLP metabolites were characterized based on rat liver microsomes (RLMs) using KCN (trapping agent) using LC-MS/MS. The main goal of the current study was to answer the question of whether the presence of a piperazine ring in the chemical structure should be always considered a structural alert. Piperazine ring in RBC and ABC was bioactivated through a metabolic sequence that involves the hydroxylation of α-carbon to the tertiary nitrogen atoms of the piperazine ring. In the case of OLP, no cyano adduct was formed due to the presence of two carbonyl groups attached to the two nitrogen atoms of the piperazine ring (neutral amide groups). From the results, piperazine ring in certain cases should not be considered as a structural alert as in the case of OLP due to the presence of two electron withdrawing group that stops the proposed toxicity. Also blocking the bioactive center (α-carbon) using steric hindrances such as methyl group, also the isosteric replacement of α-carbon hydrogen with fluoro atom can aid in reducing the toxic side effects of ABC and RCB. These experiments were done in vitro through incubation with RLMs in the presence of KCN. Also, the results are supported by data generated from in silico software. In the future, drug discovery studies using this concept could be undertaken, allowing for the development of new drugs with reasonable safety profiles. Overall, in vitro RLMs incubations and in silico experiments were able to predict successfully that the piperazine ring should not always be considered a structural alert.

Dual roles of drug or its metabolite-protein conjugate: Cutting-edge strategy of drug discovery using shotgun proteomics.

Many drugs can bind directlyto proteins or be bioactivated by metabolizing enzymes to form reactive metabolites (RMs) that rapidly bind to proteins to form drug-protein conjugates or metabolite-protein conjugates (DMPCs). The close relationship between DMPCs and idiosyncratic adverse drug reactions (IADRs) has been recognized; drug discovery teams tend to avoid covalent interactions in drug discovery projects. Covalent interactions in DMPCs can provide high potency and long action duration and conquer the intractable targets, inspiring drug design, and development. This forms the dual role feature of DMPCs. Understanding the functional implications of DMPCs in IADR control and therapeutic applications requires precise identification of these conjugates from complex biological samples. While classical biochemical methods have contributed significantly to DMPC detection in the past decades, the low abundance and low coverage of DMPCs have become a bottleneck in this field. An emerging transformation towardshotgun proteomics is on the rise. The evolving shotgun proteomics techniques offer improved reproducibility, throughput, specificity, operability, and standardization. Here, we review recent progress in the systematic discovery of DMPCs using shotgun proteomics. Furthermore, the applications of shotgun proteomics supporting drug development, toxicity mechanism investigation, and drug repurposing processes are also reviewed and prospected.

Molecular Fingerprinting by Single Cell Clone Analysis in Adverse Drug Reaction (ADR) Assessment.

Causality assessment for idiosyncratic ADRs mainly relies on epidemiology, signal detection and less often on proven or plausible mechanistic evidence of the drug at a cellular or organ level. Distinct clones of cells can exist within organs of individual patients, some conferring susceptibility to well-recognised Adverse Drug Reactions (ADRs). Recent advances in molecular biology have allowed the development of single-cell clonal techniques, including single-cell RNA sequencing (scRNA-seq) to molecularly fingerprint ADRs and distinguish between distinct clones of cells within organs in individuals, which may confer differing susceptibilities to ADRs. ScRNA- seq permits molecular fingerprinting of some serious ADRs, mainly in the skin, through the identification of Directly Expressed Genes (DEG) of interest within specific clones. Overexpressed DEGs provide an opportunity for targeted treatment strategies to be developed. scRN A-seq could be applied to a number of other ADRs involving tissues that can be biopsied/sampled (including skin, liver, kidney, blood, stem cells) as well as providing a molecular basis for rapid screening of potential therapeutic candidates, which may not otherwise be predictable from a class of toxicity/organ involvement. A framework for putative assessment for ADRs using scRNA-seq is proposed as well as speculating on potential regulatory implications for pharmacovigilance and drug development. Molecular fingerprinting of ADRs using scRNA-seq may allow better targeting for enhanced pharmacovigilance and risk minimisation measures for medicines with appropriate benefit-risk profiles, although cost-effectiveness and other factors, such as frequency/severity of individual ADRs and population differences, will still be relevant.

Pharmacogenetics of the cytochromes P450: Selected pharmacological and toxicological aspects.

With the availability of detailed genomic data on all 57 human cytochrome P450 genes, it is clear that there is substantial variability in gene product activity with functionally significant polymorphisms reported across almost all isoforms. This article is concerned mainly with 13 P450 isoforms of particular relevance to xenobiotic metabolism. After brief review of the extent of polymorphism in each, the relevance of selected P450 isoforms to both adverse drug reaction and disease susceptibility is considered in detail. Bleeding due to warfarin and other coumarin anticoagulants is considered as an example of a type A reaction with idiosyncratic adverse drug reactions affecting the liver and skin as type B. It is clear that CYP2C9 variants contribute significantly to warfarin dose requirement and also risk of bleeding, with a minor contribution from CYP4F2. In the case of idiosyncratic adverse drug reactions, CYP2B6 variants appear relevant to both liver and skin reactions to several drugs with CYP2C9 variants also relevant to phenytoin-related skin rash. The relevance of P450 genotype to disease susceptibility is also considered but detailed genetic studies now suggest that CYP2A6 is the only P450 relevant to risk of lung cancer with alleles associated with low or absent activity clearly protective against disease. Other cytochrome P450 genotypes are generally not predictors for risk of cancer or other complex disease development.

HLA-associated adverse drug reactions - scoping review.

Alleles of the human leukocyte antigen (HLA) system have been associated with the occurrence of idiosyncratic adverse drug reactions (ADRs). Accordingly, it is assumed that pre‐emptive testing for the presence of certain HLA alleles (HLA‐typing) could prevent these ADRs in carriers. In order to perceive the current evidence for HLA‐associated ADRs, we conducted a scoping review according to the Preferred Reporting Items for Systematic Reviews and Meta‐Analyses (PRISMA). The literature search on PubMed and on Embase was carried out on the July 8 and 9, 2020, respectively. To be included in the scoping review, the studies had to investigate an association of any HLA‐associated ADR with any small molecule approved and available on the Swiss market. We considered English and German primary literature published since 2002. A total of 149 studies were included, whereof most were retrospective, whereas one was a prospective randomized controlled trial. The majority of the studies (n = 33) described the association of HLA‐B*15:02 with carbamazepine. It was not possible to directly compare the studies, as they were too heterogeneous in terms of the ADR definition, the HLA alleles, the number of participants, and the study types. Therefore, we summarized the results in a descriptive manner. Even if an interpretation of the outcomes remains open, the descriptive overview revealed the prevailing complexity and uncertainty in the field. For the future, consistent definitions on the different phenotypes need to be established and applied and the reporting of association studies should follow a harmonized structure.

Reactive Metabolites from Thiazole-Containing Drugs: Quantum Chemical Insights into Biotransformation and Toxicity.

Drugs containing thiazole and aminothiazole groups are known to generate reactive metabolites (RMs) catalyzed by cytochrome P450s (CYPs). These RMs can covalently modify essential cellular macromolecules and lead to toxicity and induce idiosyncratic adverse drug reactions. Molecular docking and quantum chemical hybrid DFT study were carried out to explore the molecular mechanisms involved in the biotransformation of thiazole (TZ) and aminothiazole (ATZ) groups leading to RM epoxide, S-oxide, N-oxide, and oxaziridine. The energy barrier required for the epoxidation is 13.63 kcal/mol, that is lower than that of S-oxidation, N-oxidation, and oxaziridine formation (14.56, 17.90, and 20.20, kcal/mol respectively). The presence of the amino group in ATZ further facilitates all the metabolic pathways, for example, the barrier for the epoxidation reaction is reduced by ∼2.5 kcal/mol. Some of the RMs/their isomers are highly electrophilic and tend to form covalent bonds with nucleophilic amino acids, finally leading to the formation of metabolic intermediate complexes (MICs). The energy profiles of these competitive pathways have also been explored.

Case Report of Acute Liver Failure Induced By Isotretinoin Medication

Introduction: Drug induced liver injury or DILI is any injury to the liver by a medication, herb, or dietary supplement. Ranking as the first cause of acute liver failure in the USA and Europe, spectrum of clinical presentation may range from asymptomatic elevated liver function test to ALF. Approximately 20 new cases of DILI per 100,000 persons occur each year worldwide. Classified as intrinsic (with the most common cause being acetaminophen), and idiosyncratic adverse drug reaction (including mostly those related to antibiotics, NSAID drugs, and isoniazid). Isotretinoin is indicated to treat severe inflammatory acne that is refractory to antibiotics or topical agents; Although it has a high margin of safety, adverse effects include transaminasitis, like many retinoids, but unlike acitretin and etretinate, isotretinoin has not been clearly implicated in cases of clinically apparent acute liver failure. We report a case of 31 year old lady on isotretinoin therapy for her acnea since 8 month with poor follow up, presenting with acute liver failure to our emergency department. Case Presentation: 31 year old lady , NKDFA, on isotretinoin for her acne, started 8 month ago at a dose 40mg daily, is brought by her family for decrease level of consciousness and increasing jaundice since around 5 days associated with mild abdominal disconfort. Intubated for GCS of 3, laboratory tests showed prolonged INR and elevated total bilirubin, mainly direct, with elevated transaminase levels, all work up for other etiologies turned negative, and patient was diagnosed with isotretinoin inducing acute liver failure. Discussion: Hepatotoxicity manifesting by liver test abnormalities, occur in up to 15% of patients on isotretinoin. These liver test abnormalities are usually asymptomatic and resolve spontaneously even without discontinuation of therapy in most cases. Severe liver injury due to isotretinoin is exceedingly rare: The acute liver failure was only been described with etretinate and acitretin and not with isotretinoin therapy. Risk factors for DILI include older age, female sex, African American, pharmacological risk (including daily dosage, degree of lipophilicity and extent of hepatic metabolism), preexisting liver disease and Host Genetic Factors. An important association was found between the dose of oral medication and hepatotoxicity in the United States and Sweden, in addition to a positive association between higher drug lipophilicity and DILI in condition to be coupled with high dose ingestion. Our patient meets the criteria for sex and for the pharmacological characteristic of isotretinoin (which is a highly lipophilic drug and was ingested at 40mg daily). DILI may cause cholestatic or hepatocellular liver injury or mixed on the basis of the R value, In addition, studies have showed that DILI in females is more often hepatocellular and may be associated with a more severe course, which can result in the need for liver transplant, or death and all that were compatible with our case. As the disorder is rare, there are no specific biomarkers for diagnosis of idiosyncratic DILI, and diagnosis is made by exclusion. Recent advances in the diagnosis of DILI include the recognition of the importance of the establishment of clinical networks to refine causality assessment estimated by RUCAM score and also the use of expert panels in the diagnosis of DILI [3]. The calculated RUCAM score for our case is equal to 8, indicating probable drug reaction. Concerning acute liver failure, the most widely accepted definition from the American Association for the Study of Liver Diseases (AASLD) is ‘’evidence of coagulation abnormality, usually an international normalized ratio above 1.5, and any degree of mental alteration (encephalopathy) in a patient without preexisting liver disease and with an illness of less than 26 weeks’ duration’’. Based on all above, the presentation of our patient was typical for an acute liver failure induced by the drug isotretinoin. The only curative treatment of drug induced acute liver failure is liver transplantation. Conclusion: This is probably the first case reporting an acute liver failure induced by isotretinoin therapy. Strict monitoring of liver tests is highly recommended for patients receiving isotretinoin at regular intervals, with close observation and follow up, because, although rare, it may induce an acute liver failure with deleterious results. Future works must include a discovery of an early markers of DILI, for early detection and prevention in the high risk patients.

Case Report of Acute Liver Failure Induced By Isotretinoin Medication

Introduction: Drug induced liver injury or DILI is any injury to the liver by a medication, herb, or dietary supplement. Ranking as the first cause of acute liver failure in the USA and Europe, spectrum of clinical presentation may range from asymptomatic elevated liver function test to ALF. Approximately 20 new cases of DILI per 100,000 persons occur each year worldwide. Classified as intrinsic (with the most common cause being acetaminophen), and idiosyncratic adverse drug reaction (including mostly those related to antibiotics, NSAID drugs, and isoniazid).

Case Report of Acute Liver Failure Induced By Isotretinoin Medication

Introduction: Drug induced liver injury or DILI is any injury to the liver by a medication, herb, or dietary supplement. Ranking as the first cause of acute liver failure in the USA and Europe, spectrum of clinical presentation may range from asymptomatic elevated liver function test to ALF. Approximately 20 new cases of DILI per 100,000 persons occur each year worldwide. Classified as intrinsic (with the most common cause being acetaminophen), and idiosyncratic adverse drug reaction (including mostly those related to antibiotics, NSAID drugs, and isoniazid). Isotretinoin is indicated to treat severe inflammatory acne that is refractory to antibiotics or topical agents; Although it has a high margin of safety, adverse effects include transaminasitis, like many retinoids, but unlike acitretin and etretinate, isotretinoin has not been clearly implicated in cases of clinically apparent acute liver failure. We report a case of 31 year old lady on isotretinoin therapy for her acnea since 8 month with poor follow up, presenting with acute liver failure to our emergency department. Case Presentation: 31 year old lady , NKDFA, on isotretinoin for her acne, started 8 month ago at a dose 40mg daily, is brought by her family for decrease level of consciousness and increasing jaundice since around 5 days associated with mild abdominal disconfort. Intubated for GCS of 3, laboratory tests showed prolonged INR and elevated total bilirubin, mainly direct, with elevated transaminase levels, all work up for other etiologies turned negative, and patient was diagnosed with isotretinoin inducing acute liver failure. Discussion: Hepatotoxicity manifesting by liver test abnormalities, occur in up to 15% of patients on isotretinoin. These liver test abnormalities are usually asymptomatic and resolve spontaneously even without discontinuation of therapy in most cases. Severe liver injury due to isotretinoin is exceedingly rare: The acute liver failure was only been described with etretinate and acitretin and not with isotretinoin therapy. Risk factors for DILI include older age, female sex, African American, pharmacological risk (including daily dosage, degree of lipophilicity and extent of hepatic metabolism), preexisting liver disease and Host Genetic Factors. An important association was found between the dose of oral medication and hepatotoxicity in the United States and Sweden, in addition to a positive association between higher drug lipophilicity and DILI in condition to be coupled with high dose ingestion. Our patient meets the criteria for sex and for the pharmacological characteristic of isotretinoin (which is a highly lipophilic drug and was ingested at 40mg daily). DILI may cause cholestatic or hepatocellular liver injury or mixed on the basis of the R value, In addition, studies have showed that DILI in females is more often hepatocellular and may be associated with a more severe course, which can result in the need for liver transplant, or death and all that were compatible with our case. As the disorder is rare, there are no specific biomarkers for diagnosis of idiosyncratic DILI, and diagnosis is made by exclusion. Recent advances in the diagnosis of DILI include the recognition of the importance of the establishment of clinical networks to refine causality assessment estimated by RUCAM score and also the use of expert panels in the diagnosis of DILI [3]. The calculated RUCAM score for our case is equal to 8, indicating probable drug reaction. Concerning acute liver failure, the most widely accepted definition from the American Association for the Study of Liver Diseases (AASLD) is ‘’evidence of coagulation abnormality, usually an international normalized ratio above 1.5, and any degree of mental alteration (encephalopathy) in a patient without preexisting liver disease and with an illness of less than 26 weeks’ duration’’. Based on all above, the presentation of our patient was typical for an acute liver failure induced by the drug isotretinoin. The only curative treatment of drug induced acute liver failure is liver transplantation. Conclusion: This is probably the first case reporting an acute liver failure induced by isotretinoin therapy. Strict monitoring of liver tests is highly recommended for patients receiving isotretinoin at regular intervals, with close observation and follow up, because, although rare, it may induce an acute liver failure with deleterious results. Future works must include a discovery of an early markers of DILI, for early detection and prevention in the high risk patients.

Bio-activation of simeprevir in liver microsomes and characterization of its glutathione conjugates by liquid chromatography coupled to ultrahigh-resolution quadrupole time-of-flight mass spectrometry

Liquid chromatography coupled to a triple quadrupole and, alternatively, to an ultrahigh-resolution quadrupole time-of-flight (UHR-QqTOF) mass spectrometers was used to collect qualitative and quantitative information from incubations of the anti-hepatitis C drug simeprevir with human and rat liver microsomes, respectively, supplemented with NADPH and glutathione. For this, different chromatographic methods using two different chromatographic columns, Kinetex® 2.6 µm C18 (50 × 3 mm) and Atlantis T3 (100 Å, 3 µm, 4.6 mm × 150 mm), have been employed. For determination and structural characterization of the reactive metabolites, we used information obtained from high-resolution mass spectrometry, namely accurate mass data to calculate the elemental composition, accurate MS/MS fragmentation patterns for confirmation of structural proposals, and the high mass spectral resolution to eliminate false-positive peaks. In this study, the use of high-resolution mass spectrometry (HR-MS) enabled the identification of 19 simeprevir metabolites generated by O- respectively N-demethylation, oxidation, dehydrogenation, hydrolysis, and formation of glutathione conjugates. The in silico study provides insights into the sites of simeprevir most amenable to reactions involving cytochrome P450. The developed methods have been successfully applied to analyze simeprevir and its metabolites simultaneously; based on this data, potential metabolic pathways of simeprevir are discussed. In general, the obtained results demonstrate that simeprevir is susceptible to form reactive simeprevir-glutathione adducts and cyclopropansulfonamide, which may explain the implication of simeprevir in idiosyncratic adverse drug reactions (IADRs) or hepatotoxicity.

Genome-Wide Association Study of Metamizole-Induced Agranulocytosis in European Populations.

Agranulocytosis is a rare yet severe idiosyncratic adverse drug reaction to metamizole, an analgesic widely used in countries such as Switzerland and Germany. Notably, an underlying mechanism has not yet been fully elucidated and no predictive factors are known to identify at-risk patients. With the aim to identify genetic susceptibility variants to metamizole-induced agranulocytosis (MIA) and neutropenia (MIN), we conducted a retrospective multi-center collaboration including cases and controls from three European populations. Association analyses were performed using genome-wide genotyping data from a Swiss cohort (45 cases, 191 controls) followed by replication in two independent European cohorts (41 cases, 273 controls) and a joint discovery meta-analysis. No genome-wide significant associations (p < 1 × 10−7) were observed in the Swiss cohort or in the joint meta-analysis, and no candidate genes suggesting an immune-mediated mechanism were identified. In the joint meta-analysis of MIA cases across all cohorts, two candidate loci on chromosome 9 were identified, rs55898176 (OR = 4.01, 95%CI: 2.41–6.68, p = 1.01 × 10−7) and rs4427239 (OR = 5.47, 95%CI: 2.81–10.65, p = 5.75 × 10−7), of which the latter is located in the SVEP1 gene previously implicated in hematopoiesis. This first genome-wide association study for MIA identified suggestive associations with biological plausibility that may be used as a stepping-stone for post-GWAS analyses to gain further insight into the mechanism underlying MIA.

Screening Trimethoprim Primary Metabolites for Covalent Binding to Albumin.

Modification of endogenous proteins by drugs and drug metabolites are thought to be a cause of idiosyncratic adverse drug reactions (IADRs). Trimethoprim (TMP) is a commonly prescribed antibiotic that has been implicated in IADRs; however, there is no known mechanism by which this drug or its metabolites modify proteins. This study describes the results of screening trimethoprim and its primary metabolites for the ability to covalently modify human serum albumin (HSA). The first step of the screen was in vitro reactions of the compounds with HSA followed by western blotting with antisera specific to drug-modified proteins. Compounds with positive signal in the western blot were then screened using an untargeted peptide profiling method to discover modified peptides. This strategy identified two sites in HSA that are modified by incubation with a TMP metabolite, α-hydroxy trimethoprim (Cα-OH-TMP).

Ranitidine Induced Hepatotoxicity: A Review

Background: Ranitidine (RAN) is one of the common drugs associated with idiosyncratic adverse drug reactions (IADRs) in humans. It was found to be associated with severe adverse drug reactions due to the presence of contaminants such as N-Nitrosodimethylamine (NDMA) which is claimed to be carcinogenic. As a consequence, on April 1, 2020, United States Food and Drug Administration (USFDA) had decided to call off all the RAN products from the market. The exact cause of RAN associated idiosyncratic hepatotoxicity is not clear yet. Purpose: To summarize and analyze the reason behind the withdrawal of RAN products from the market and whether ranitidine will be available again in future or will FDA withdraw approvals of ranitidine National Drug Authority (NDA) and an abbreviated new drug application (ANDA)? Methods: We performed a systematic PubMed/MEDLINE search of studies investigating the reason behind the withdrawal of RAN products and explored the possible mechanism associated with RAN induced hepatotoxicity. Conclusion: RAN induced liver injury is difficult to diagnose and study because of its relative rarity and unpredictive occurrence. Recent studies suggest that most of the RAN associated idiosyncratic reactions may lead to hepatocyte damage, followed by a series of events, such as activation of specific T- and B-cells, release of proinflammatory mediators like TNFα, interleukins, various cytokines and chemokines. The exact cause of RAN associated idiosyncratic hepatotoxicity is not clear yet. More studies must be carried out on this to know about the exact reason behind RAN associated hepatotoxicity.

Recent Advances and Outlook for the Isosteric Replacement of Anilines.

Many promising drug candidates and pharmaceutical compounds fail due to idiosyncratic adverse drug reactions (IADRs), often arising from the formation of reactive metabolites. Among the "structural alerts" responsible, anilines are well-known to undergo deleterious metabolic processing, yet isosteric replacement strategies remain limited. Herein we discuss current art and potential new avenues of saturated isosteres to mitigate aniline-related toxicities.

Understanding Idiosyncratic Toxicity: Lessons Learned from Drug-Induced Liver Injury.

Idiosyncratic adverse drug reactions (IADRs) encompass a diverse group of toxicities that can vary by drug and patient. The complex and unpredictable nature of IADRs combined with the fact that they are rare makes them particularly difficult to predict, diagnose, and treat. Common clinical characteristics, the identification of human leukocyte antigen risk alleles, and drug-induced proliferation of lymphocytes isolated from patients support a role for the adaptive immune system in the pathogenesis of IADRs. Significant evidence also suggests a requirement for direct, drug-induced stress, neoantigen formation, and stimulation of an innate response, which can be influenced by properties intrinsic to both the drug and the patient. This Perspective will provide an overview of the clinical profile, mechanisms, and risk factors underlying IADRs as well as new approaches to study these reactions, focusing on idiosyncratic drug-induced liver injury.

Designing around Structural Alerts in Drug Discovery.

Cumulative research over several decades has implicated the involvement of reactive metabolites in many idiosyncratic adverse drug reactions (IADRs). Consequently, "avoidance" strategies have been inserted into drug discovery paradigms, which include the exclusion of structural alerts and possible termination of reactive metabolite-positive compounds. Several noteworthy examples where reactive metabolite-related liabilities have been resolved through structure-metabolism studies are presented herein. Considerable progress has also been made in addressing the limitations of the avoidance strategy and further refining the process of managing reactive metabolite issues in drug development. These efforts primarily stemmed from the observation that numerous drugs, which contain structural alerts and/or form reactive metabolites, are devoid of ADRs. The Perspective also dwells into an analysis of the structural alert/reactive metabolite concept with a discussion of risk mitigation tactics to support the progression of reactive metabolite-positive drug candidates.