Warfarin monitoring using prothrombin time is problematic due to marked variability in the responsiveness of different thromboplastins to the anticoagulant effects of the drug.
Warfarin is a very effective antithrombotic drug, but its dosage must be monitored carefully because its metabolic clearance varies among patients and the risk of clinically important bleeding rises sharply when the upper limit of the effective range is exceeded. Warfarin therapy is usually monitored by the prothrombin time (PT).1The PT is sensitive to three of the four vitamin K-dependent procoagulant clotting factors and is obtained by adding a mixture of calcium and thromboplastin to citrated plasma. The termthromboplastindescribes a phospholipid-protein extract of tissues, usually lung, brain, or placenta, that contains both the tissue factor and the phospholipid necessary to promote the activation of factor X by factor VII.1,2The PT is a simple test, but its interpretation can be problematic because thromboplastins vary markedly in their responsiveness to the anticoagulant effects of warfarin depending on their source and method of preparation.3-9As a
Jack Hirsh (Sat,) conducted a editorial in Warfarin therapy monitoring. Warfarin was evaluated. Warfarin monitoring using prothrombin time is problematic due to marked variability in the responsiveness of different thromboplastins to the anticoagulant effects of the drug.