Warfarin

Many indications. 1/100 population now taking warfarin. Monitored by 402 INR (International Normalized Ratio) which is a standardised PT ratio. Target INR typically 2.5. Over anticoagulation common. More likely with target INR >2.5 and when other drugs, particularly antibiotics, are prescribed. Avoided by lowest possible target INR, testing within 5-7d of any change in other drug therapy and patient awareness of change in bleeding tendency.

Over anticoagulation due to warfarin increasingly treated with small doses of vitamin K. For example INR >8.0 give 1-2.5mg vitamin K PO.

Note: severe overanticoagulation complicated by major bleeding should be reversed by emergency administration of factor concentrate containing vitamin K-dependent factors, e.g. beriplex. Recombinant factor VIIa may be considered if beriplex or similar concentrate is unavailable. Alternatively FFP can be given but reversal is often incomplete and massive volumes of FFP have to be given.

BCSH Guidelines on oral anticoagulation. Br J Haematol 101, 374-387 (1998). ^ www.bcshguidelines.com/pdf/bjh715.pdf

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