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The Figure highlights additional considerations for using these agents in the clinical setting. For example, blood tests are not used to guide dosing but they can be used to assess compliance or washout if a patient comes in with a stroke. The factor Xa inhibitors do affect the INR, therefore if a patient comes in and the INR is normal, the patient has not had a recent dose of rivaroxaban or apixaban. Dabigatran affects the thrombin time (TT), the ecarin clotting time (ECT), and the activated partial thromboplastin time (APTT); if the patient comes in with a stroke or bleed and those tests are normal, then the event was not caused by a recent dose of dabigatran. If a patient has been taking an anticoagulant, a blood test can wash out the drug prior to surgery.
An important issue for physicians will be reversal of anticoagulant effect. This was covered in the first presentation, especially the fact that vitamin K can take up to 24 hours to halve the INR of warfarin when it is elevated. New antidotes for the NOACs are being developed, but they are not ready yet, and therefore at present the only remedies are fresh frozen plasma (FFP), prothrombin complex concentrates, activated charcoal, and dialysis.
Reiffel JA. Am J Med 2013; 126: 00-00.