In the first move of its kind, the US Food and Drug Administration (FDA) - the agency responsible for regulating food, drugs and biological medical products - has recommended a genetic test prior to the prescription of a drug, Warfarin, in order to gauge potential patient response.
Warfarin, sold under the trade name Coumadin, is a potent blood-thinning agent used to treat patients who have suffered blood clots in their legs or lungs or are at increased risk of having a stroke. However, it is infamous for its slim therapeutic window outside of which small variations in dosing may lead to serious complications: two in every hundred patients prescribed the drug suffer haemorrhagic or thrombotic episodes. After insulin, it is the most common prescription drug cited in emergency hospital admissions.
Two genes - known as CYP2 and VKOR - have been implicated in patient response to Warfarin. Among people at any one time there can be a number of different versions of any gene - so-called 'variants' - which, whilst retaining their functionality, contain the odd single-letter code changes. Research has shown that individuals who have the variants CYP2C9 and VKORC1 are known to react in a more extreme manner to Warfarin. The variant genes alongside patient age, height, body weight, and interacting drugs could explain up to 55 per cent of the variability seen in patient response.
The genetic test proposed would be employed to identify the presence of the gene variants and then the dose of Warfarin could be altered accordingly - i.e. a lower dose given to those patients carrying the variants. 'Although genetic testing can currently identify who has these genetic variants, more studies are needed to explore the precise starting dose for these patients', said Larry Lesko, director of the FDA's clinical pharmacology office.
The FDA has not insisted that the test be done prior to the prescription of Warfarin. Instead, it has requested that genetic testing information is added to Coumadin's label. Bristol-Myers, a manufacturer of the drug, agreed to the FDA's recommendation. 'The company is committed to working with regulatory authorities as science evolves to appropriately inform physicians on the use of our medicines', said spokesman Jeff Macdonald.
The move by the FDA is seen as a much anticipated forerunner for the epoch of personalised medicine - an era where instead of a generic treatment for a disease, treatment will be based on detailed information on an individual's genotype and clinical data. A much vaunted movement, born from the field of pharmacogenetics, it has, to date, failed to produce much in the way of tangible treatment for patients.
'Today's approved labelling change is one step in our commitment to personalised medicine', said Commissioner of Food and Drugs Andrew C. von Eschenbach, M.D. He added: 'By using modern science to get the right drug in the right dose for the right patient, FDA will further enhance the safety and effectiveness of the medicines Americans depend on'.
Sources and References
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U.S. orders genetic data on blood-thinner risks
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For the First Time, FDA Recommends Gene Testing
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FDA Approves Updated Warfarin (Coumadin) Prescribing Information
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