A clinically significant interaction between warfarin and simvastatin is unique to carriers of the CYP2C9*3 allele

Insight into Risk Factors, Pharmacogenetics/Genomics, and Management of Adverse Drug Reactions in Elderly: A Narrative Review

The European Medicine Agency (EMA) has defined Adverse Drug Reactions (ADRs) as "a noxious and unintended response to a medicine", not including poisoning, accidental, or intentional overdoses. The ADR occurrence differs based on the approach adopted for defining and detecting them, the characteristics of the population under study, and the research setting. ADRs have a significant impact on morbidity and mortality, particularly among older adults, and represent a financial burden for health services. Between 30% and 60% of ADRs might be predictable and preventable, emerging as a result of inappropriate prescription, drug chemistry inherent toxicity, cell-specific drug toxicity, age- and sex-related anomalies in drug absorption, distribution, metabolism, and elimination (ADME), and drug-drug interactions (DDIs) in combination therapies or when a patient is treated with different drugs for concomitant disorders. This is particularly important in chronic diseases which require long-term treatments. Rapid developments in pharmacogenetics/genomics have improved the understanding of ADRs accompanied by more accurate prescriptions and reduction in unnecessary costs. To alleviate the burden of ADRs, especially in the elderly, interventions focused on pharmaceutical principles, such as medication review and reconciliation, should be integrated into a broader assessment of patients' characteristics, needs, and health priorities. Digital health interventions could offer valuable solutions to assist healthcare professionals in identifying inappropriate prescriptions and promoting patient adherence to pharmacotherapies.

Drug-Drug-Gene Interactions in Cardiovascular Medicine

Cardiovascular disease remains a leading cause of both morbidity and mortality worldwide. It is widely accepted that both concomitant medications (drug-drug interactions, DDIs) and genomic factors (drug-gene interactions, DGIs) can influence cardiovascular drug-related efficacy and safety outcomes. Although thousands of DDI and DGI (aka pharmacogenomic) studies have been published to date, the literature on drug-drug-gene interactions (DDGIs, cumulative effects of DDIs and DGIs) remains scarce. Moreover, multimorbidity is common in cardiovascular disease patients and is often associated with polypharmacy, which increases the likelihood of clinically relevant drug-related interactions. These, in turn, can lead to reduced drug efficacy, medication-related harm (adverse drug reactions, longer hospitalizations, mortality) and increased healthcare costs. To examine the extent to which DDGIs and other interactions influence efficacy and safety outcomes in the field of cardiovascular medicine, we review current evidence in the field. We describe the different categories of DDIs and DGIs before illustrating how these two interact to produce DDGIs and other complex interactions. We provide examples of studies that have reported the prevalence of clinically relevant interactions and the most implicated cardiovascular medicines before outlining the challenges associated with dealing with these interactions in clinical practice. Finally, we provide recommendations on how to manage the challenges including but not limited to expanding the scope of drug information compendia, interaction databases and clinical implementation guidelines (to include clinically relevant DDGIs and other complex interactions) and work towards their harmonization; better use of electronic decision support tools; using big data and novel computational techniques; using clinically relevant endpoints, preemptive genotyping; ensuring ethnic diversity; and upskilling of clinicians in pharmacogenomics and personalized medicine.

Rates of Divergent Pharmacogenes in a Psychiatric Cohort of Inpatients with Depression-Arguments for Preemptive Testing

Background: The international drug agencies annotate pharmacogenes for many years. Pharmacogenetic testing is thus far only established in few settings, assuming that only few patients are actually affected by drug-gene interactions. Methods: 108 hospitalized patients with major depressive disorder were genotyped for CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP3A4, CYP3A5, NAT2, DPYD; VKORC1 and TMTP. Results: We found 583 (mean 5.4, median 5) divergent phenotypes (i.e., divergent from the common phenotypes considered normal, e.g., extensive metabolizer) in the 12 analyzed pharmacokinetic genes. The rate for at least one divergent phenotype was 100% in our cohort for CYP, but also for all 12 important pharmacogenes: patients had at least two divergent phenotypes. Compared to a large Danish cohort, CYP2C9 NM and IM status, CYP2C19 UM, CYP2D6 UM and DYPD (GAS 0, 1, 2) genotypes differed statistical significantly. For CYP2D6 and CYP2C19, 13% of the patients were normal metabolizers for both enzymes in our cohort, but this value was 27.3% in the Danish cohort, which is a highly significant difference (p < 0.0001). Conclusion: Divergent phenotypes in pharmacogenes are not the exception, but the rule. Patients with divergent phenotypes seem more prone for hospitalization, emphasizing the need for pre-emptive testing to avoid inefficacy and adverse drug effects in all patients.

Opioid-Related Genetic Polymorphisms of Cytochrome P450 Enzymes after Total Joint Arthroplasty: A Focus on Drug-Drug-Gene Interaction with Commonly Coprescribed Medications

Pharmacogenomic testing, together with the early detection of drug-drug-gene interactions (DDGI) before initiating opioids, can improve the selection of dosage and reduce the risk of adverse drug interactions and therapeutic failures following Total Joint Arthroplasty. The variants of CYP genes can mediate DDGI. Orthopedic surgeons should become familiar with the genetic aspect of opioid use and abuse, as well as the influence of the patient genetic makeup in opioid selection and response, and polymorphic variants in pain modulation.

Drug Interactions Affecting Oral Anticoagulant Use

Oral anticoagulants (OACs) are medications commonly used in patients with atrial fibrillation and other cardiovascular conditions. Both warfarin and direct oral anticoagulants are susceptible to drug-drug interactions (DDIs). DDIs are an important cause of adverse drug reactions and exact a large toll on the health care system. DDI for warfarin mainly involve moderate to strong inhibitors/inducers of cytochrome P450 (CYP) 2C9, which is responsible for the elimination of the more potent S-isomer of warfarin. However, inhibitor/inducers of CYP3A4 and CYP1A2 may also cause DDI with warfarin. Recognition of these precipitating agents along with increased frequency of monitoring when these agents are initiated or discontinued will minimize the impact of warfarin DDI. Direct oral anticoagulants are mainly affected by medications strongly affecting the permeability glycoprotein (P-gp), and to a lesser extent, strong CYP3A4 inhibitors/inducers. Dabigatran and edoxaban are affected by P-gp modulation. Strong inducers of CYP3A4 or P-gp should be avoided in all patients taking direct oral anticoagulant unless previously proven to be otherwise safe. Simultaneous strong CYP3A4 and P-gp inhibitors should be avoided in patients taking apixaban and rivaroxaban. Concomitant antiplatelet/anticoagulant use confers additive risk for bleeding, but their combination is unavoidable in many cases. Minimizing duration of concomitant anticoagulant/antiplatelet therapy as indicated by evidence-based clinical guidelines is the best way to reduce the risk of bleeding.

Risk of Gastrointestinal Bleeding on Treatment With Statin Alone or With Concomitant Administration of Warfarin: A Systematic Review and Meta-analysis of 5.3 Million Participants

OBJECTIVE

This study aimed to comprehensively evaluate the risk of gastrointestinal bleeding (GIB) with statin monotherapy or with concomitant warfarin use.

DATA SOURCES

PubMed, Web of Science, and EMBASE (via Scopus) were searched for observational studies that reported the risk of GIB in adults on statin therapy or with concomitant warfarin use until August 28, 2021.

STUDY SELECTION AND DATA EXTRACTION

Observational studies evaluating the risk of GIB in adults (age >18 years) on statin medication or concomitant use with warfarin were included.

DATA SYNTHESIS

In all, 14 studies with a total of 5 235 123 participants, reporting 48 677 GIB events (43 734 from statin users and 4943 from users of statin combined with warfarin), were included in the analyses. The pooled analysis revealed no difference in the risk of GIB with statin monotherapy (relative risk [RR]: 0.65; 95% CI: 0.42-1.02) or concomitant statin + warfarin use (RR: 0.97; 95% CI: 0.91-1.02). Prior use of statin was not associated with GIB risk (RR: 0.88; 95% CI: 0.63-1.22), whereas a shorter duration of statin use (<5 years) was associated with a lower risk of GIB (RR: 0.42; 95% CI: 0.18-0.97).

RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE

This analysis provides strong evidence on the association between statin use (with/without warfarin) and risk of GIB.

CONCLUSION

Statin alone or combined with warfarin was not significantly associated with either an increased or decreased risk of GIB. The GIB risk was significantly lower when statins were used for a short duration (<5 years). The putative relationship between statins and GIB in warfarin users warrant further investigation.

Risk prediction of drug-drug interaction potential of phenytoin and miconazole topical formulations

The drug-drug interaction (DDI) risk of phenytoin with several topical formulations of miconazole is still unclear. The present investigation conducted in vitro-in vivo extrapolation to predict the potential risks. Our data indicated that miconazole potently inhibited phenytoin hydroxylation in both pooled human liver microsomes (HLMs) and recombinant cytochrome P450 2C9 (CYP2C9) with the K_i values of 125 ± 7 nM and 30 ± 2 nM, respectively. Quantitative prediction of DDI risk suggests that, beside intravenous administration or swallowed tablet, combination of phenytoin and miconazole high dose oral gel or buccal tablet may also result in a clinically significant increase of phenytoin AUC (>53%) by the inhibition of miconazole against phenytoin hydroxylation, consequently a higher frequency of adverse events, while the coadministration of miconazole vaginal formulation and phenytoin will be safe.

Multimorbidity, polypharmacy, and drug-drug-gene interactions following a non-ST elevation acute coronary syndrome: analysis of a multicentre observational study

BACKGROUND

The number of patients living with co-existing diseases is growing. This study aimed to assess the extent of multimorbidity, medication use, and drug- and gene-based interactions in patients following a non-ST elevation acute coronary syndrome (NSTE-ACS).

METHODS

In 1456 patients discharged from hospital for a NSTE-ACS, comorbidities and multimorbidity (≥ 2 chronic conditions) were assessed. Of these, 698 had complete drug use recorded at discharge, and 652 (the 'interaction' cohort) had drug use and actionable genotypes available for CYP2B6, CYP2C9, CYP2C19, CYP2D6, CYP3A5, DPYD, F5, SLCO1B1, TPMT, UGT1A1, and VKORC1. The following drug interactions were investigated: pharmacokinetic drug-drug (DDIs) involving CYPs (CYPs above, plus CYP1A2, CYP2C8, CYP3A4), SLCO1B1, and P-glycoprotein; drug-gene (DGIs); drug-drug-gene (DDGIs); and drug-gene-gene (DGGIs). Interactions predicted to be 'substantial' were defined as follows: DDIs due to strong inhibitors/inducers, DGIs due to variant homozygous/compound heterozygous genotypes, and DDGIs/DGGIs where the constituent DDI/DGI(s) both influenced the victim drug in the same direction.

RESULTS

In the whole cohort, 727 (49.9%) patients had multimorbidity. Non-linear relationships between age and increasing comorbidities and decreasing coronary intervention were observed. There were 98.1% and 39.8% patients on ≥ 5 and ≥ 10 drugs, respectively (from n = 698); women received more non-cardiovascular drugs than men (median (IQR) 3 (1-5) vs 2 (1-4), p = 0.014). Overall, 98.7% patients had at least one actionable genotype. Within the interaction cohort, 882 interactions were identified in 503 patients (77.1%), of which 346 in 252 patients (38.7%) were substantial: 59.2%, 11.6%, 26.3%, and 2.9% substantial interactions were DDIs, DGIs, DDGIs, and DGGIs, respectively. CYP2C19 (49.5% of all interactions) and SLCO1B1 (18.4%) were involved in the largest number of interactions. Multimorbidity (p = 0.019) and number of drugs (p = 9.8 × 10-10) were both associated with patients having ≥ 1 substantial interaction. Multimorbidity (HR 1.76, 95% CI 1.10-2.82, p = 0.019), number of drugs (HR 1.10, 95% CI 1.04-1.16, p = 1.2 × 10-3), and age (HR 1.05, 95% CI 1.03-1.07, p = 8.9 × 10-7), but not drug interactions, were associated with increased subsequent major adverse cardiovascular events.

CONCLUSIONS

Multimorbidity, polypharmacy, and drug interactions are common after a NSTE-ACS. Replication of results is required; however, the high prevalence of DDGIs suggests integrating co-medications with genetic data will improve medicines optimisation.

Effects of acid and lactone forms of statins on S-warfarin 7-hydroxylation catalyzed by human liver microsomes and recombinant CYP2C9 variants (CYP2C9.1 and CYP2C9.3)

The inhibition of CYP2C9-mediated warfarin metabolism by acid or lactone forms of statin converted in the body and effects of CYP2C9 genetic variants on their inhibition are not fully understood. Here, the effects of acid and lactone forms of statins on S-warfarin 7-hydroxylation were investigated in vitro. S-Warfarin 7-hydroxylase activities of human liver microsomes (HLMs), recombinant CYP2C9.1 (rCYP2C9.1), and rCYP2C9.3 (Ile359Leu variant) in the presence of statins were determined by high-performance liquid chromatography. Lactone forms of atorvastatin, lovastatin, pitavastatin, pravastatin, rosuvastatin, and simvastatin inhibited the activity of HLMs more potently than the corresponding acid forms, whereas fluvastatin acid showed stronger inhibition than fluvastatin lactone. When the effects of statins on rCYP2C9 variants were examined, inhibition profiles of acid versus lactone forms of statins except for fluvastatin were similar between rCYP2C9.1 and rCYP2C9.3. However, the degrees of inhibition by atorvastatin lactone, fluvastatin acid, fluvastatin lactone, lovastatin lactone, and pitavastatin lactone (K_i values) were significantly different between these variants. These results indicated that lactone forms of statins other than fluvastatin showed more potent inhibition of CYP2C9-catalyzed S-warfarin 7-hydroxylation than the corresponding acid forms. Furthermore, our results indicated that Ile359Leu substitution in CYP2C9 affected the inhibitory potencies of statins.

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.

Drug-drug-gene interactions and adverse drug reactions

The economic and health burden caused by adverse drug reactions has increased dramatically in the last few years. This is likely to be mediated by increasing polypharmacy, which increases the likelihood for drug–drug interactions. Tools utilized by healthcare practitioners to flag potential adverse drug reactions secondary to drug–drug interactions ignore individual genetic variation, which has the potential to markedly alter the severity of these interactions. To date there have been limited published studies on impact of genetic variation on drug–drug interactions. In this review, we establish a detailed classification for pharmacokinetic drug–drug–gene interactions, and give examples from the literature that support this approach. The increasing availability of real-world drug outcome data linked to genetic bioresources is likely to enable the discovery of previously unrecognized, clinically important drug–drug–gene interactions.

The effect of simvastatin on warfarin anticoagulation: a Swedish register-based nationwide cohort study

PURPOSE

Some data indicate that simvastatin may increase the anticoagulative effect in patients treated with warfarin, but the evidence is scarce. The aim of the present study was to investigate how the anticoagulative effect of warfarin is affected by the initiation of simvastatin in a very large patient sample.

METHODS

In a retrospective cohort study, we included 5637 individuals on warfarin treatment initiating simvastatin. INR values and warfarin doses were calculated week-by-week during co-treatment. Data were obtained from two large Swedish warfarin registers and from the Swedish Prescribed Drug Register.

RESULTS

INR increased from 2.43 at baseline to 2.58, 4 weeks after simvastatin initiation, and did not stabilize until the last quarter of the year studied. Consequently, the proportion of patients with an INR above 3 increased from around 8 to 15%.

CONCLUSIONS

In conclusion, initiation of simvastatin resulted in moderately increased INR values and subsequent dose decreases in patients already on warfarin. In order to avoid the increased risk of bleeding, the initiation of simvastatin may be accompanied by closer INR monitoring.

Pharmacogenomic Next-Generation DNA Sequencing: Lessons from the Identification and Functional Characterization of Variants of Unknown Significance in CYP2C9 and CYP2C19

CYP2C9 and CYP2C19 are highly polymorphic pharmacogenes; however, clinically actionable genetic variability in drug metabolism due to these genes has been limited to a few common alleles. The identification and functional characterization of less-common open reading frame sequence variation might help to individualize therapy with drugs that are substrates for the enzymes encoded by these genes. The present study identified seven uncharacterized variants each in CYP2C9 and CYP2C19 using next-generation sequence data for 1013 subjects, and functionally characterized the encoded proteins. Constructs were created and transiently expressed in COS-1 cells for the assay of protein concentration and enzyme activities using fluorometric substrates and liquid chromatography- tandem mass spectrometry with tolbutamide (CYP2C9) and (S)-mephenytoin (CYP2C19) as prototypic substrates. The results were compared with the SIFT, Polyphen, and Provean functional prediction software programs. Cytochrome P450 oxidoreductase (CPR) activities were also determined. Positive correlations were observed between protein content and fluorometric enzyme activity for variants of CYP2C9 (P < 0.05) and CYP2C19 (P < 0.0005). However, CYP2C9 709G>C and CYP2C19 65A>G activities were much lower than predicted based on protein content. Substrate intrinsic clearance values for CYP2C9 218C>T, 343A>C, and CYP2C19 337G>A, 518C>T, 556C>T, and 557G>A were less than 25% of wild-type allozymes. CPR activity levels were similar for all variants. In summary, sequencing of CYP2C9 and CYP2C19 in 1013 subjects identified low-frequency variants that had not previously been functionally characterized. In silico predictions were not always consistent with functional assay results. These observations emphasize the need for high-throughput methods for pharmacogene variant mutagenesis and functional characterization.

Pharmacogenomics research and clinical implementation in Brazil

We searched PubMed entries and the Lattes database of Brazilian Pharmacogenetics Network investigators, for pharmacogenetic/genomic (PGx) studies in the Brazilian population, focusing on the drugs and genes included in the Clinical Pharmacogenetics Implementation Consortium (CPIC) guidelines. Warfarin was the most extensively studied drug in a PGx context: a genomewide association study targeting warfarin stable dose identified significant signals in VKORC1 and CYP2C9, several PGx dosing algorithms were developed based on these and other genes, and the implications of population admixture on extrapolation of dosing recommendations in the CPIC guidelines were examined. A study in renal transplanted patients disclosed association of CYP3A5*6 and CYP3A5*7 with tacrolimus dosing, which led to addition of these variants to CYP3A5*3 in the CPIC tacrolimus guideline. Studies verified predisposition of HIV-positive carriers of UGT1A1*28 to severe atazanavir-induced hyperbilirubinaemia, intolerance to 5-fluorouracyl in gastrointestinal cancer patients with deleterious DPYD variants, failure of HCV-infected carriers of IFNL3 rs12979860 to obtain a sustained viral response to PEG-IFN-α, and hypersensitivity reactions to abacavir in HIV-positive carriers of HLA-B*57:01. No prospective analyses of drug therapy outcomes or cost-effectiveness assessments of PGx-guided therapy were found. In conclusion, the limited adoption of PGx-informed drug prescription in Brazil reflects combination of recognized barriers to PGx implementation worldwide plus factors specific to the Brazilian population. The latter include rarity/absence of genetic variants on which international PGx guidelines are based (eg HLA-B*15.02 for phenytoin and carbamazepine) and the caveat of extrapolating to the admixed Brazilian population, guidelines based on categorical variables, such as continental ancestry (eg warfarin guidelines), "race" or ethnicity.

Complex Drug-Drug-Gene-Disease Interactions Involving Cytochromes P450: Systematic Review of Published Case Reports and Clinical Perspectives

Drug pharmacokinetics (PK) is influenced by multiple intrinsic and extrinsic factors, among which concomitant medications are responsible for drug-drug interactions (DDIs) that may have a clinical relevance, resulting in adverse drug reactions or reduced efficacy. The addition of intrinsic factors affecting cytochromes P450 (CYPs) activity and/or expression, such as genetic polymorphisms and diseases, may potentiate the impact and clinical relevance of DDIs. In addition, greater variability in drug levels and exposures has been observed when such intrinsic factors are present in addition to concomitant medications perpetrating DDIs. This variability results in poor predictability of DDIs and potentially dramatic clinical consequences. The present review illustrates the issue of complex DDIs using systematically searched published case reports of DDIs involving genetic polymorphisms, renal impairment, cirrhosis, and/or inflammation. Current knowledge on the impact of each of these factors on drug exposure and DDIs is summarized and future perspectives for the management of such complex DDIs in clinical practice are discussed, including the use of advanced Computerized Physician Order Entry (CPOE) systems, the development of model-based dose optimization strategies, and the education of healthcare professionals with respect to personalized medicine.

A narrative review of the safety concerns of deprescribing in older adults and strategies to mitigate potential harms

INTRODUCTION

As with prescribing or continuing medications, deprescribing brings with it the potential for harm as well as benefit. Uncertainty and avoidance of harm has been reported as a barrier to deprescribing in practice and may contribute to continuation of inappropriate medications.

AREAS COVERED

This narrative review covers four main safety concerns/potential harms of deprescribing in older adults: adverse drug withdrawal events, return of medical condition(s), reversal of drug-drug interactions and damage to the doctor-patient relationship. These are discussed in relation to medications in general, with some examples of medication classes used to illustrate the potential safety concerns. The majority of these harms can be minimized or even prevented by using a patient-centered, structured deprescribing process with planning, tapering and close monitoring during, and after medication withdrawal.

EXPERT OPINION

More research is needed into the safety concerns of deprescribing, however, avenues exist during drug development and post-marketing surveillance to gain knowledge on this topic. Questions remain about when it is suitable to discontinue certain medications/medication classes and there is uncertainty about the harms and benefits of both medication continuation and discontinuation in complex older adults.

Effect of Addition of a Statin to Warfarin on Thromboembolic Events in Japanese Patients With Nonvalvular Atrial Fibrillation and Diabetes Mellitus

Statins have been shown to decrease stroke risk in patients with cardiovascular risk factors but not to prevent recurrence of ischemic stroke in patients with atrial fibrillation (AF). The present subanalysis aimed to clarify the efficacy of combined use of warfarin and statins in patients with nonvalvular AF (NVAF) with coronary artery disease, diabetes mellitus (DM), or hypertension. The effects of adding statins to warfarin were compared with those of warfarin alone in patients with NVAF with the data set of J-RHYTHM Registry, a prospective, observational study with a 2-year follow-up. End points included thromboembolism, major hemorrhage, all-cause mortality, and cardiovascular mortality. Of 7,406 patients with NVAF and follow-up data, 6,404 patients received warfarin at baseline. Of these, 1,605 patients also received a statin. Patients in the warfarin plus statin group showed significantly lower all-cause mortality compared with those on warfarin alone (hazard ratio [HR] 0.57, 95% confidence interval [CI] 0.38 to 0.87, p = 0.0089), although thromboembolic event rates did not differ significantly (HR 0.73, 95% CI 0.44 to 1.20, p = 0.21). In contrast, in 1,223 patients with DM, the warfarin plus statin group showed significantly lower thromboembolic event rates than the warfarin-alone group (HR 0.33, 95% CI 0.11 to 0.96, p = 0.041). Interestingly, in patients with coronary artery disease or with hypertension, the addition of statin to warfarin did not decrease the frequency of thromboembolic events. In conclusion, in Japanese patients with NVAF with DM, a combination of warfarin and a statin could be clinically beneficial for preventing thromboembolic events.

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.

Rivaroxaban-Induced Hemorrhage Associated with ABCB1 Genetic Defect

We report a patient who presented a non-ST segment elevation myocardial infarction in the context of severe normocytic hypochromic anemia related to gastrointestinal bleeding, 3 months after switching anticoagulant from the vitamin K antagonist acenocoumarol to the direct oral anticoagulant rivaroxaban. High levels of both anti-Xa activity and rivaroxaban plasma concentrations were measured despite rivaroxaban withdrawal, suggesting reduced elimination/drug clearance. Estimated half-life was 2–3 times longer than usually reported. The patient is a homozygous carrier of ABCB1 variant alleles, which could have participated to reduced elimination of rivaroxaban. Furthermore, CYP3A4/5 phenotyping showed moderately reduced enzyme activity. Drug-drug interaction with simvastatin may have contributed to decreased rivaroxaban elimination. Although in the present case moderate acute renal failure probably played a role, more clinical data are required to elucidate the impact of ABCB1 polymorphism on rivaroxaban pharmacokinetics and bleeding complications.

The effect of carbamazepine on warfarin anticoagulation: a register-based nationwide cohort study involving the Swedish population

BACKGROUND

There are data indicating that the interaction between warfarin and carbamazepine results in decreased warfarin efficacy. However, the evidence on the magnitude of and interindividual differences in susceptibility to this interaction has remained scarce.

OBJECTIVES

To investigate the effect of carbamazepine on warfarin anticoagulation and warfarin maintenance doses by the use of data from three nationwide registries.

PATIENTS/METHODS

In a retrospective cohort study including 166 patients, warfarin doses were compared 2-4 weeks before and 10-13 weeks after initiation of cotreatment with carbamazepine. In addition, warfarin doses and International Normalized Ratio (INR) values were calculated week-by-week during cotreatment. Data on prescribed warfarin doses and INR measurements were obtained from two large Swedish warfarin registers. Data on carbamazepine use were retrieved from the Swedish Prescribed Drug Register.

RESULTS

The average warfarin doses were 49% (95% confidence interval 43-56) higher during carbamazepine treatment. The INR decreased upon carbamazepine initiation, and subtherapeutic INR levels were observed in 79% of all patients during the fifth week of cotreatment. Warfarin maintenance dose increases exceeding 50% and 100% were observed in 59% and 17% of patients, respectively.

CONCLUSIONS

Four of five warfarin-treated patients in whom cotreatment with carbamazepine was initiated experienced subtherapeutic anticoagulative effect within 3-5 weeks. The warfarin dose was subsequently increased by 49%, a change that differed widely between patients. In order to avoid thrombosis and ischemic stroke, carbamazepine initiation should be accompanied by close INR monitoring to better meet the anticipated increase in dose demand.

Co-Prescribing of Potentially Interacting Drugs during Warfarin Therapy - A Population-Based Register Study

We analysed the occurrence of co-prescribing of potentially interacting drugs during warfarin therapy in the community-dwelling population of Finland. We identified drugs having interaction potential with warfarin using the Swedish Finnish INteraction X-referencing drug-drug interaction database (SFINX) and obtained data on drug purchases from the nationwide Prescription Register. We defined warfarin users as persons purchasing warfarin in 2010 (n = 148,536) and followed them from their first prescription in 2010 until the end of the calendar year. Co-prescribing was defined as at least 1-day overlap between warfarin and interacting drug episodes. In addition, we identified persons who initiated warfarin therapy between 1 January 2007 and 30 September 2010 (n = 110,299) and followed these incident users for a 3-month period since warfarin initiation. Overall, 74.4% of warfarin users were co-prescribed interacting drugs. Co-prescribing covered 46.4% of the total person-years of warfarin exposure. Interacting drugs that should be avoided with warfarin were co-prescribed for 13.4% of warfarin users. The majority of the co-prescriptions were for drugs that are not contraindicated during warfarin therapy but require special consideration. Among incident users, 57.1% purchased potentially interacting drugs during the 3-month period after initiation, while 9.0% purchased interacting drugs that should be avoided with warfarin. To conclude, the occurrence of co-prescribing of potentially interacting drugs was high during warfarin therapy. Our findings highlight the importance of close monitoring of warfarin therapy and the need for further studies on the clinical consequences of co-prescribing of interacting drugs with warfarin.

Impact of CYP2C9 polymorphisms on the vulnerability to pharmacokinetic drug-drug interactions during acenocoumarol treatment

AIM

The objective of this study was to investigate the impact of CYP2C9 polymorphisms and drug-drug interactions on the risk of overanticoagulation in patients treated with acenocoumarol, a vitamin K antagonist.

MATERIALS & METHODS

A prospective observational study was performed on patients starting acenocoumarol (n = 115). CYP2C9 genotypes were assessed. Data on International Normalized Ratio, comedications and doses of acenocoumarol were collected during the first 35 days of therapy. Overanticoagulation was defined as the occurrence of at least one International Normalized Ratio ≥4.

RESULTS

The presence of a CYP2C9 inhibitor or a CYP2C9 polymorphisms statistically increased the risk of overanticoagulation (hazard ratio [HR]: 2.8, p < 0.001 and HR: 1.7, p = 0.04, respectively). The presence of CYP2C9 polymorphisms almost tripled the risk of overanticoagulation (HR: 2.91, p = 0.01) in the presence of a clinically significant drug-drug interaction.

CONCLUSION

These findings support the fact that CYP2C9 genotyping could be useful to identify patients requiring closer monitoring, especially when a drug-drug interaction is expected.

Vitamin K antagonists in heart disease: current status and perspectives (Section III). Position paper of the ESC Working Group on Thrombosis--Task Force on Anticoagulants in Heart Disease

Oral anticoagulants are a mainstay of cardiovascular therapy, and for over 60 years vitamin K antagonists (VKAs) were the only available agents for long-term use. VKAs interfere with the cyclic inter-conversion of vitamin K and its 2,3 epoxide, thus inhibiting γ-carboxylation of glutamate residues at the amino-termini of vitamin K-dependent proteins, including the coagulation factors (F) II (prothrombin), VII, IX and X, as well as of the anticoagulant proteins C, S and Z. The overall effect of such interference is a dose-dependent anticoagulant effect, which has been therapeutically exploited in heart disease since the early 1950s. In this position paper, we review the mechanisms of action, pharmacological properties and side effects of VKAs, which are used in the management of cardiovascular diseases, including coronary heart disease (where their use is limited), stroke prevention in atrial fibrillation, heart valves and/or chronic heart failure. Using an evidence-based approach, we describe the results of completed clinical trials, highlight areas of uncertainty, and recommend therapeutic options for specific disorders. Although VKAs are being increasingly replaced in most patients with non-valvular atrial fibrillation by the new oral anticoagulants, which target either thrombin or FXa, the VKAs remain the agents of choice for patients with atrial fibrillation in the setting of rheumatic valvular disease and for those with mechanical heart valves.

Evaluation of the pharmacokinetics and drug interactions of the two recently developed statins, rosuvastatin and pitavastatin

INTRODUCTION

Statins are the cornerstone of lipid-lowering therapy to reduce the risk of coronary heart disease. Rosuvastatin and pitavastatin are the two recently developed statins with less potential for drug interaction resulting in improved safety profiles.

AREAS COVERED

This review summarizes the pharmacokinetics and drug interactions of rosuvastatin and pitavastatin. The materials reviewed were identified by searching PubMed for publications using 'rosuvastatin', 'pitavastatin', 'statins', 'pharmacokinetics' and 'drug interaction' as the search terms.

EXPERT OPINION

Rosuvastatin and pitavastatin have favorable pharmacokinetic and safety profiles as their disposition does not depend on or is only marginally influenced by cytochrome P450 (CYP) enzymes, thus potentially reducing the risk of drug-drug interactions of these two statins with other drugs known to inhibit CYP enzymes. However, drug transporters play a significant role in the disposition of rosuvastatin and pitavastatin and drug interactions may occur through these. Genetic polymorphisms in drug transporters may also affect the pharmacokinetics, drug interactions and/or the lipid-lowering effect of these statins to a different extent.

Influence of the CYP2C9*3 allele on the pharmacological interaction between warfarin and simvastatin

A letter in response to: Andersson ML, Eliasson E, Lindh JD. A clinically significant interaction between warfarin and simvastatin is unique to carriers of the CYP2C9*3 allele. Pharmacogenomics 13(7), 757–762 (2012).

Influence of the CYP2C9*3 allele on the pharmacological interaction between warfarin and simvastatin: author reply

A letter in response to: Botton MR, Hutz MA & Suarez-Kurtz G. Influence of the CYP2C9*3 allele on the pharmacological interaction between warfarin and simvastatin. Pharmacogenomics 13(14), 1557–1559 (2012).