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Vitamin K antagonists: Difference between revisions
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(Created page with "<section begin="clinical biochemistry" />The '''vitamin K antagonists''' (VKAs) are a group of anticoagulants. Most vitamin K antagonists are '''''coumarins''''', so the terms are often used interchangeably. However, there exist some VKAs which are not coumarins. The most commonly used VKA by far is '''warfarin''' (Marevan®, Coumadin®). These drugs are administered orally. <section end="clinical biochemistry" /> '''Dicumarol''' is another VKA, but du...") |
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The problem with coumarins is that people respond differently to the same dose. This is because polymorphisms in the gene for ''vitamin K epoxide reductase'' change the affinity of the VKAs to the enzyme and differences in vitamin K content of diet. | The problem with coumarins is that people respond differently to the same dose. This is because polymorphisms in the gene for ''vitamin K epoxide reductase'' change the affinity of the VKAs to the enzyme and differences in vitamin K content of diet. | ||
To monitor the anticoagulant effect of warfarin, the international normalised ratio (INR) is used. INR is a standardised form of prothrombin time which is normalised so that the result is similar between different laboratory methods and equipments. The prothrombin time is first measured and then normalised by a specific equation and factor. | To monitor the anticoagulant effect of warfarin, the [[international normalised ratio]] (INR) is used. INR is a standardised form of prothrombin time which is normalised so that the result is similar between different laboratory methods and equipments. The prothrombin time is first measured and then normalised by a specific equation and factor. | ||
It’s important to start with a low dose and continuously test the INR of the patient to make sure that they’re not receiving too much (and therefore bleed too easily) or too little (and therefore have suboptimal anticoagulant effect). The dose should always be adjusted so that the INR of the patient is between 2 and 3 (between 2,5 – 3,5 in case of mechanical heart valves). INR should be measured often, initially daily but later more and more rarely (but still regularly).<section end="clinical biochemistry" /> | It’s important to start with a low dose and continuously test the INR of the patient to make sure that they’re not receiving too much (and therefore bleed too easily) or too little (and therefore have suboptimal anticoagulant effect). The dose should always be adjusted so that the INR of the patient is between 2 and 3 (between 2,5 – 3,5 in case of mechanical heart valves). INR should be measured often, initially daily but later more and more rarely (but still regularly).<section end="clinical biochemistry" /> | ||
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== Reversal == | == Reversal == | ||
The anticoagulant effect of VKA antagonists can be rapidly reversed by replacement, by administering prothrombin complex concentrate or fresh frozen plasma. Vitamin K administration also antagonises the effect but this occurs much more slowly. | The anticoagulant effect of VKA antagonists can be rapidly reversed by replacement, by administering prothrombin complex concentrate or fresh frozen plasma. Vitamin K administration also antagonises the effect but this occurs much more slowly. | ||
<noinclude>[[Category:Pharmacology]]</noinclude> | <noinclude> | ||
[[Category:Pharmacology]] | |||
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