Clopidogrel is an anti-platelet drug that is used to prevent atherosclerotic events. Patients taking anti-platelet drugs are not monitored by an INR test prior to dental extractions.
Heparin and enoxaparin, which is a low molecular weight heparin, inhibit clotting by neutralising the action of thrombin on fibrinogen and preventing the activation of prothrombin to thrombin. Patients on heparins tend to have a normal INR but their thrombin time will be increased, hence an INR is not used as a routine test for patients on these drugs.
Vitamin K is required for the synthesis of prothrombin (factor II) and factors VII, IX and X in the liver. Lack of vitamin K will cause clotting time to be increased.
Warfarin is an anti-coagulant that is monitored by regular INR tests, and patients having dental extractions must have an INR check no more than 72 hours prior to the extraction. For more information, see the National Patient Safety Agency (NPSA) website (www.npsa.nhs.uk).