A Graphic Nomogram for Warfarin Dosage Adjustment

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Abstract
We assessed the ability of a graphic nomogram to adjust steady‐state warfarin dosages and to predict international normalized ratios (INR) after a dosage change, compared with an anticoagulation clinic pharmacist and a Bayesian regression computer program. Study subjects were 108 men and 3 women receiving warfarin anticoagulation. In all patients the median absolute errors in predicted INR values for the nomogram, computer program, and pharmacist were 0.33, 0.46, and 0.48, respectively. The nomogram was significantly more precise than both other methods (p=0.036). In a subset of 50 patients who required dosage reductions, the median absolute INR prediction errors for the nomogram, computer program, and pharmacist were 0.35, 0.54, and 0.48 respectively. The nomogram was significantly more precise than the pharmacist (p=0.005) and computer (p=0.002). The ability to provide more precise dosage reductions of warfarin may be of clinical importance in light of current recommendations for higher‐intensity warfarin therapy and maintenance of higher INR values. Prospective validation of the performance of this nomogram in a routine clinical setting is warranted.

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