Genetic warfarin dosing: tables versus algorithms

Warfarin therapeutic monitoring: is 70% time in the therapeutic range the best we can do?

WHAT IS KNOWN AND OBJECTIVE

Warfarin, an oral anticoagulant, which has been in clinical use for over sixty years, remains a challenge for clinicians to utilize, given the multiplicity of items which can limit its efficacy. Our objective is to review the evidence and comment on whether INR control can be better than has been currently reported in various studies.

COMMENT

The duration of time a patient's international normalized ratio (INR) is maintained within the therapeutic range (time in the therapeutic range, TTR) for his or her particular indication for the drug impacts the effectiveness and safety of warfarin therapy. Maintaining a therapeutic INR while on warfarin is difficult, and numerous studies employing various strategies confirm the challenge, but not the impossibility of achieving a TTR above 70%.

WHAT IS NEW AND CONCLUSION

Maintaining a therapeutic INR requires a dedicated multi-faceted approach. With diligence, skill and various therapeutic strategies, a TTR >70% can be achieved.

Clinical Pharmacogenetics Implementation Consortium Guidelines for CYP2C9 and VKORC1 genotypes and warfarin dosing

Warfarin is a widely used anticoagulant with a narrow therapeutic index and large interpatient variability in the dose required to achieve target anticoagulation. Common genetic variants in the cytochrome P450-2C9 (CYP2C9) and vitamin K-epoxide reductase complex (VKORC1) enzymes, in addition to known nongenetic factors, account for ~50% of warfarin dose variability. The purpose of this article is to assist in the interpretation and use of CYP2C9 and VKORC1 genotype data for estimating therapeutic warfarin dose to achieve an INR of 2-3, should genotype results be available to the clinician. The Clinical Pharmacogenetics Implementation Consortium (CPIC) of the National Institutes of Health Pharmacogenomics Research Network develops peer-reviewed gene-drug guidelines that are published and updated periodically on http://www.pharmgkb.org based on new developments in the field.(1).

Pharmacogenetics: past, present and future

The subject area of pharmacogenetics, also known as pharmacogenomics, has a long history. Research in this area has led to fundamental discoveries, which have helped our understanding of the reasons why individuals differ in the way they handle drugs, and ultimately in the way they respond to drugs, either in terms of efficacy or toxicity. However, not much of this knowledge has been translated into clinical practice, most drug-gene associations that have some evidence of clinical validity have not progressed to clinical settings. Advances in genomics since 2000, including the ready availability of data on the variability of the human genome, have provided us with unprecedented opportunities to understand variability in drug responses, and the opportunity to incorporate this into patient care. This is only likely to occur with a systematic approach that evaluates and overcomes the different translational gaps in taking a biomarker from discovery to clinical practice. In this article, I explore the history of pharmacogenetics, appraise the current state of research in this area, and finish off with suggestions for progressing in the field in the future.