Pharmacology and pharmacogenetics of warfarin and other coumarins when used with supplements

Meta-analysis of randomized controlled trials reveals an improved clinical outcome of using genotype plus clinical algorithm for warfarin dosing

Previous studies have raised interest in using the genotyping of CYP2C9 and VKORC1 to guide warfarin dosing. However, there is lack of solid evidence to prove that genotype plus clinical algorithm provides improved clinical outcomes than the single clinical algorithm. The results of recent reported clinical trials are paradoxical and needs to be systematically evaluated. In this study, we aim to assess whether genotype plus clinical algorithm of warfarin is superior to the single clinical algorithm through a meta-analysis of randomized controlled trials (RCTs). All relevant studies from PubMed and reference lists from Jan 1, 1995 to Jan 13, 2014 were extracted and screened. Eligible studies included randomized trials that compared clinical plus pharmacogenetic algorithms group to single clinical algorithm group using adult (≥ 18 years) patients with disease conditions that require warfarin use. We further used fix-effect models to calculate the mean difference or the risk ratios (RRs) and 95% CIs to analyze the extracted data. The statistical heterogeneity was calculated using I(2). The percentage of time within the therapeutic INR range was considered to be the primary clinical outcome. The initial search strategy identified 50 citations and 7 trials were eligible. These seven trials included 1,910 participants, including 960 patients who received genotype plus clinical algorithm of warfarin dosing and 950 patients who received clinical algorithm only. We discovered that the percentage of time within the therapeutic INR range of the genotype-guided group was improved compared with the standard group in the RCTs when the initial standard dose was fixed (95% CI 0.09-0.40; I(2) = 47.8%). However, for the studies using non-fixed initial doses, the genotype-guided group failed to exhibit statistically significant outcome compared to the standard group. No significant difference was observed in the incidences of adverse events (RR 0.94, 95% CI 0.84-1.04; I(2) = 0%, p = 0.647) and death rates (RR 1.36, 95% CI 0.46-4.05; I(2) = 10.4%, p = 0.328) between the two groups. Allocation to genotype plus clinical algorithm may be associated with a significant improvement of the percentage of time within the therapeutic INR range for patients adopting fixed dose of warfarin. The incidence of total adverse events and death rates did not differ between these two groups. Further experiments need to be conducted to confirm these findings.

Pre-treatment with puerarin affects pharmacokinetics of warfarin, but not clopidogrel, in experimental rats

The present study was designed to determine the effects of puerarin pre-treatment on the pharmacokinetics of the oral anticoagulant agent warfarin and the antiplatelet agent clopidogrel in rats. In the treatment group, rats was gavaged with warfarin or clopidogrel after repeated treatment with puerarin at intraperitoneal doses of 20, 60, or 200 mg·kg(-1) for 7 days, while rats in the control group were administrated only with the same dose warfarin or clopidogrel. Plasma samples were obtained at the prescribed times and analyzed by liquid chromatography tandem mass spectrometry (LC-MS/MS). The results showed that rats treated with puerarin at all the test doses of 20, 60 and 200 mg·kg(-1) were found to affect the pharmacokinetics of warfarin, but not clopidogrel, suggesting a potential herb-drug interaction between puerarin and warfarin.

Oral anticoagulant therapy in patients receiving haemodialysis: is it time to abandon it?

Oral anticoagulant (OAC) therapy in haemodialysis patients causes a great deal of controversy. This is because a number of pro- and anticoagulant factors play an important role in end-stage renal failure due to the nature of the disease itself. In these conditions, the pharmacokinetic and pharmacodynamic properties of the OACs used change as well. In the case of the treatment of venous thromboembolism, the only remaining option is OAC treatment according to regimens used for the general population. Prevention of HD vascular access thrombosis with the use of OACs is not very effective and can be dangerous. However, OAC treatment in patients with atrial fibrillation in dialysis population may be associated with an increase in the incidence of stroke and mortality. Doubts should be dispelled by prospective, randomised studies; at the moment, there is no justification for routine use of OACs in the above-mentioned indications. In selected cases of OAC therapy in this group of patients, it is absolutely necessary to control and monitor the applied treatment thoroughly. Indications for the use of OACs in patients with end-stage renal disease, including haemodialysis patients, should be currently limited.

Personalized echocardiography: clinical applications of advanced echocardiography and future directions

Future cardiology practice will be increasingly individualized, and thus to maintain its central role, echocardiography must keep pushing to expand the boundaries of real-time data acquisition from tissue and fluid motion, and yet still provide efficient and timely data analysis that leads to succinct, clear clinical recommendations tailored to each person in our care. In this article, recent efforts to expand echocardiography techniques into an era of increasingly personalized cardiology, including advances in color-coded tissue Doppler, 3D echocardiography and complex exercise stress echocardiography are described. The common metric for success in each of these efforts is the development of robust and institutionally supportable echocardiography protocols for specific cardiology disease populations that currently may be underdiagnosed and/or undertreated. The common result in each case should be the creation of new guidelines that can supplement the current standard protocols advocated by professional echocardiography organizations.

Pharmacogenetic predictors of adverse events and response to chemotherapy in metastatic colorectal cancer: results from North American Gastrointestinal Intergroup Trial N9741

PURPOSE

With three available chemotherapy drugs for advanced colorectal cancer (CRC), response rate (RR) and survival outcomes have improved with associated morbidity, accentuating the need for tools to select optimal individualized treatment. Pharmacogenetics identifies the likelihood of adverse events or response based on variants in genes involved in drug transport, metabolism, and cellular targets.

PATIENTS AND METHODS

Germline DNA was extracted from 520 patients on the North American Gastrointestinal Intergroup N9741 study. Three study arms were evaluated: IFL (fluorouracil [FU] + irinotecan [IRN]), FOLFOX (FU + oxaliplatin), and IROX (IRN + oxaliplatin). Information on adverse events, response, and disease-free survival was available. Thirty-four variants in 15 candidate genes for analysis based on previous associations with adverse events or outcome were assessed. Genotyping was performed using pyrosequencing.

RESULTS

All variants were polymorphic. The homozygous UGT1A1*28 allele observed in 9% of patients was associated with risk of grade 4 neutropenia in patients on IROX (55% v 15%; P = .002). Deletion in GSTM1 was associated with grade 4 neutropenia after FOLFOX (28% v 16%; P = .02). Patients with a homozygous variant genotype for GSTP1 were more likely to discontinue FOLFOX because of neurotoxicity (24% v 10%; P = .01). The presence of a CYP3A5 variant was significantly associated with RR on IFL (29% v 60%; P = .0074). Most previously published genotype-toxicity or -efficacy relationships were not validated in this study.

CONCLUSION

This study provides a platform to evaluate pharmacogenetic predictors of response or severe adverse events in advanced CRC. Pharmacogenetic studies can be conducted in multicenter trials, and our findings demonstrate that with continued research, clinical application is practical.

Role of warfarin pharmacogenetic testing in clinical practice

Chronic oral anticoagulation with warfarin is difficult to maintain within the therapeutic range and requires frequent monitoring and dose adjustments. Variations in two genes, VKORC1 and CYP2C9, have been associated with variation in warfarin metabolism among individuals. Patients with CYP2C9*2 and *3 variants have longer times to dose stabilization and are at higher risk of serious and life-threatening bleeding. VKORC1 polymorphisms significantly influence time to first therapeutic warfarin range, and variants in this gene determine low-, intermediate- and high-warfarin dose requirements. The prevalence of CYP2C9 and VKORC1 polymorphisms vary among different ethnic groups, and can account for over 30% of variance in warfarin dose. Recent studies suggest that the pharmacogenomics-guided dosing algorithm can accurately predict warfarin dosage and might reduce adverse events. We aim to review the pharmacogenetics of warfarin metabolism and the clinical role of genetic testing for warfarin therapy.

Warfarin pharmacogenetics

Significant interest in the pharmacogenetics of warfarin therapy has been triggered with the recent package insert update that highlights the potential role of pharmacogenetics in improving the safety and effectiveness of warfarin. We review the evidence of the influence of the two key genes of interest, the cytochrome P450 2C9 gene, CYP2C9, and the vitamin K epoxide reductase complex 1 gene, VKORC1, on warfarin response and discuss the implications of current knowledge for clinical practice. The influence of CYP2C9 and VKORC1 genotypes on warfarin dose requirements has been consistently demonstrated in diverse racial and ethnic patient groups in observational studies and randomized clinical trials. Dosing algorithms have been developed that incorporate clinical, demographic, and genetic information to help select a warfarin starting dose. Furthermore, CYP2C9 variant genotypes have been associated with a significantly increased risk of serious bleeding events. However, evidence to date from prospective, controlled studies has not demonstrated an added benefit of incorporating genotype-guided therapy in improving anticoagulation control or in preventing or reducing the risk of hemorrhagic or thromboembolic complications. Research efforts designed to evaluate the effectiveness of genotype-guided therapy in improving outcomes are under way. However, the routine use of CYP2C9 and VKORC1 genotyping in the general patient population who begin warfarin therapy is not supported by evidence currently available.

Management of warfarin-related intracerebral hemorrhage

Warfarin-related intracerebral hemorrhage (WICH) is a medical and neurosurgical emergency with a 1-month mortality of approximately 50%. Warfarin is commonly is used in patients with atrial fibrillation to prevent ischemic stroke and to prevent progression of deep vein thrombosis to pulmonary embolism. Owing to the ageing population, and increased incidence of atrial fibrillation with age and warfarin use, the incidence of WICH is expected to rise in the future. When WICH occurs, immediate discontinuation of warfarin with rapid warfarin reversal remains the first-line intervention, often with neurosurgical intervention. The optimal agent for rapid warfarin anticoagulation reversal remains to be defined owing to the lack of prospective randomized trials. We review current literature and prospects for future research for this devastating neurologic emergency.

Randomized Trial of Genotype-Guided Versus Standard Warfarin Dosing in Patients Initiating Oral Anticoagulation

Background— Pharmacogenetic-guided dosing of warfarin is a promising application of “personalized medicine” but has not been adequately tested in randomized trials.

Methods and Results— Consenting patients (n=206) being initiated on warfarin were randomized to pharmacogenetic-guided or standard dosing. Buccal swab DNA was genotyped for CYP2C9 *2 and CYP2C9 * 3 and VKORC1 C1173T with a rapid assay. Standard dosing followed an empirical protocol, whereas pharmacogenetic-guided dosing followed a regression equation including the 3 genetic variants and age, sex, and weight. Prothrombin time international normalized ratio (INR) was measured routinely on days 0, 3, 5, 8, 21, 60, and 90. A research pharmacist unblinded to treatment strategy managed dose adjustments. Patients were followed up for up to 3 months. Pharmacogenetic-guided predicted doses more accurately approximated stable doses ( P <0.001), resulting in smaller ( P =0.002) and fewer ( P =0.03) dosing changes and INRs ( P =0.06). However, percent out-of-range INRs (pharmacogenetic=30.7%, standard=33.1%), the primary end point, did not differ significantly between arms. Despite this, when restricted to wild-type patients (who required larger doses; P =0.001) and multiple variant carriers (who required smaller doses; P <0.001) in exploratory analyses, results (pharmacogenetic=29%, standard=39%) achieved nominal significance ( P =0.03). Multiple variant allele carriers were at increased risk of an INR of ≥4 ( P =0.03).

Conclusions— An algorithm guided by pharmacogenetic and clinical factors improved the accuracy and efficiency of warfarin dose initiation. Despite this, the primary end point of a reduction in out-of-range INRs was not achieved. In subset analyses, pharmacogenetic guidance showed promise for wild-type and multiple variant genotypes.