Oral anticoagulation: a critique of recent advances and controversies

The Outlier in All of Us: Why Implementing Pharmacogenomics Could Matter for Everyone

The field of pharmacogenomics originally emerged in the 1950s from observations that a few rare individuals had unexpected, severe reactions to drugs. As recently as just 6 years ago, prominent views on the subject had largely remained unchanged, with authors from the US Food and Drug Administration (FDA) citing the purpose of pharmacogenetics as "tailoring treatment for the outliers." It should not be surprising if this is the prevailing view--the best-studied pharmacogenomic drug examples are indeed just that, genetic explanations of extreme responses or susceptibilities among usually a very small fraction of the human population. Thiopurine methyltransferase (TPMT) deficiency as a cause of severe myelosuppression upon treatment with azathioprine or mercaptopurine is found as a heterozygous trait in only ∼ 10% of patients, and homozygous (deficiency) carriers are even more rare--occurring in fewer than 1 in 300 patients. Malignant hyperthermia resulting from inhaled anesthetics and succinylcholine is believed to have a genetic incidence of only about 1 in 2000 people.

Overcoming regulatory challenges in the development of companion diagnostics for monitoring and safety

Concurrent development and co-approval of a companion diagnostic (CDx) with a corresponding drug is ideal, but often unfeasible. Because of limited exposure to a drug in clinical trials, crucial information on safety is sometimes revealed only after approval. Therefore, a CDx for monitoring/safety is often developed after approval of a corresponding drug. However, regulatory guidance is insufficient if contemporaneous development is not possible, thereby leaving plenty of opportunities for improvement with respect to pharmacovigilance and retrospective validation of the CDx. Furthermore, global harmonization of guidance on how to incorporate new scientific information from retrospective analyses of biomarkers should lead to the establishment of more evidence for the development of CDx for approved drugs.

Novel regulatory variant detected on the VKORC1 haplotype that is associated with warfarin dose

AIM

Warfarin dose requirement is associated with VKORC1 rs9923231, and we studied whether it is a functional variant.

MATERIALS & METHODS

We selected variants in linkage disequilibrium with rs9923231 that bind transcription factors in an allele-specific way. Representative haplotypes were cloned or constructed, nuclear protein binding and transcriptional activity were evaluated.

RESULTS

rs56314408C>T and rs2032915C>T were detected in a liver enhancer in linkage disequilibrium with rs9923231. The rs56314408-rs2032915 C-C haplotype preferentially bound nuclear proteins and had higher transcriptional activity than T-T and the African-specific T-C. A motif for TFAP2A/C was disrupted by rs56314408T. No difference in transcriptional activity was detected for rs9923231G>A.

CONCLUSION

Our results supported an activating role for rs56314408C, while rs9923231G>A had no evidence of being functional.

Efficacy, safety and tolerability of rivaroxaban for the secondary prevention of stroke in patients with atrial fibrillation in clinical practice

Aim: To evaluate the efficacy, safety and tolerability of rivaroxaban for the secondary prevention of stroke in patients with atrial fibrillation in clinical practice. Methods: Patients treated with rivaroxaban for secondary prevention of stroke/transient ischemic attack attended at a cerebrovascular disease unit were consecutively included in a noninterventional and prospective study. Results: 89 patients (median age 77 years, CHADS2 = 4, HAS-BLED = 3, follow-up = 15 months) were included. Rivaroxaban was started early after the cerebrovascular event (median 5 days for stroke and 3 days for transient ischemic attack). Stroke recurrence occurred in only one patient (annual rate, 0.82%). Eight cases of clinically significant bleeding were recorded (annual rate, 6.58%), of which two were major (annual rate, 1.64%) and one intracranial (annual rate, 0.82%). Medication persistence was very good. Conclusion: Our data show that the early treatment with rivaroxaban is well tolerated, efficacious and safe for secondary prevention of real-life atrial fibrillation patients.

Pharmacogenetic Markers of Drug Efficacy and Toxicity

The action of a drug is dictated by its pharmacokinetic and pharmacodynamics properties, both of which can vary in different individuals because of environmental and genetic factors. Pharmacogenetics, the study of genetic factors determining drug response, has the potential to improve clinical outcomes through targeting therapies, individualizing dosing, preventing adverse drug reactions, and potentially rescuing previously failed therapies. Although there have been significant advances in pharmacogenetics over the last decade, only a few have been translated into clinical practice. However, with new rapid genotyping technologies, regulatory modernization, novel clinical trial designs, systems approaches, and integration of pharmacogenetic data into decision support systems, there is hope that pharmacogenetics, as an important component of the overall drive towards personalized medicine, will advance more quickly in the future. There will continue to be a need for collaboration between centers all over the world, and multisector working, capitalizing on the current data revolution.

Variation in warfarin prescribing and dosing in the UK: a national survey of anticoagulation clinics

WHAT IS KNOWN AND OBJECTIVE

Clinical practice in the initiation, prescribing, dosing and monitoring of warfarin in the UK varies, but this has not been adequately documented. The objective was to undertake a survey on current clinical practice in this area, and how it compares with national guidelines that have been developed by the British Committee for Standards in Haematology.

METHODS

A national online survey of anticoagulation clinics was performed using Survey Monkey(®) . The survey was designed to capture data for prescribing, dosing and monitoring of anticoagulation with warfarin.

RESULTS

Of 85 clinics who responded to the survey, most were run by secondary care (68%), facilitated by specialist nurses (58%) and followed standard guidelines for the management of warfarin (87%). The majority of clinics indicated their target international normalized ratio (INR) for patients with atrial fibrillation (AF) (69/73; 94·5%) was between 2·0 and 3·0, but the indicated target INR for mechanical heart valves was more variable. Initiation and loading dosing regimens were a major source of variability with uncertainty surrounding individual patient factors such as age, ethnicity and BMI.

WHAT IS NEW AND CONCLUSIONS

Current practice amongst UK anticoagulation clinics largely follows current national guidelines but better guidance on dosing, taking into account factors that determine interindividual variability in daily warfarin dose requirements would improve and standardize oral anticoagulation with warfarin.

Parsing interindividual drug variability: an emerging role for systems pharmacology

There is notable interindividual heterogeneity in drug response, affecting both drug efficacy and toxicity, resulting in patient harm and the inefficient utilization of limited healthcare resources. Pharmacogenomics is at the forefront of research to understand interindividual drug response variability, but although many genotype-drug response associations have been identified, translation of pharmacogenomic associations into clinical practice has been hampered by inconsistent findings and inadequate predictive values. These limitations are in part due to the complex interplay between drug-specific, human body and environmental factors influencing drug response and therefore pharmacogenomics, whilst intrinsically necessary, is by itself unlikely to adequately parse drug variability. The emergent, interdisciplinary and rapidly developing field of systems pharmacology, which incorporates but goes beyond pharmacogenomics, holds significant potential to further parse interindividual drug variability. Systems pharmacology broadly encompasses two distinct research efforts, pharmacologically-orientated systems biology and pharmacometrics. Pharmacologically-orientated systems biology utilizes high throughput omics technologies, including next-generation sequencing, transcriptomics and proteomics, to identify factors associated with differential drug response within the different levels of biological organization in the hierarchical human body. Increasingly complex pharmacometric models are being developed that quantitatively integrate factors associated with drug response. Although distinct, these research areas complement one another and continual development can be facilitated by iterating between dynamic experimental and computational findings. Ultimately, quantitative data-derived models of sufficient detail will be required to help realize the goal of precision medicine.