A re-appraisal of warfarin control in the treatment of deep vein thrombosis and / or pulmonary embolism.

Abstract

Warfarin is commonly used for management of deep vein thrombosis (DVT) and pulmonary embolism (PE), controlling therapy by means of the International Normalized Ratio (INR). To identify differences in INR results between patients with thromboembolic and haemorrhagic complications and controls. Two nested case-control studies from within a controlled trial of the duration of warfarin therapy (47 thrombotic and 16 haemorrhagic complications). Patients whose thromboembolism failed to resolve during treatment or recurred during or after treatment had non-significantly lower INR levels than matched controls (geometric mean 2.2 versus 2.3, p = 0.12). Patients with haemorrhage also had not statistically significant lower INR levels than their matched controls (2.1 versus 2.3, p = 0.22). The variability of INR levels was similar in both case groups and controls. The mean percentage of INR levels in the therapeutic range 2 - 3 was almost identical in thrombotic cases and controls (56.5% versus 56.1%). Compared to the haemorrhagic group, better control was achieved in controls (61.5% versus 43.0%, p=0.01), but controls had slightly more INR values above the therapeutic range (12.1% versus 10.5%, p = 0.74) whilst haemorrhagic cases had more INR values below the therapeutic range (46.6% versus 26.4%, p = 0.03). In this study, higher INR levels were not associated with haemorrhage suggesting that, for patients being treated for DVT/PE, a modest increase in the target therapeutic range could be considered.