Randomized comparison of warfarin dosing quality between the Hamilton nomogram and a commercial computer system.

Hypothesis: Mean TTR of patients managed with the commercial computer system is non-inferior to management with the validated Hamilton Nomogram.

Warfarin has a variable effect and many potential food and drug interactions. To have an optimal therapeutic effect the International Normalized Ratio (INR) needs to be maintained within the therapeutic target range. The time that a patient spends within the therapeutic target range is an intermediate quality indicator for patient outcomes and should be optimized. For this purpose, we use in our anticoagulation clinic the simple two-step Hamilton nomogram, which has been validated by Kim et al. who showed that the nomogram improved INR control for warfarin maintenance compared with expertise-based dosing in our anticoagulation clinic (see references). Computer systems are also known to outperform expertise-based dosing, but no direct comparison of a computer system with a simple nomogram has been assessed. In this single-center randomized controlled clinical trial we will compare the simple two-step Hamilton nomogram with the widely used computerized dosing management system DAWN AC regarding their effect on time in therapeutic range for patients on maintenance dosing with target range 2-3.

Inclusion Criteria:

• On warfarin maintenance therapy
• INR target range 2-3
• At least 3 historical INRs on maintenance therapy
• At least 1 historical INR in the last 3 months

Exclusion Criteria:

• Participation in another study
• On multiple pill strengths