A Randomized and Clinical Effectiveness Trial Comparing Two Pharmacogenetic Algorithms and Standard Care for Individualizing Warfarin Dosing (CoumaGen-II)

Study Questions:

Can pharmacogenetic testing improve dosing efficiency and safety over standard care for dosing warfarin therapy?


The authors reported the results of CoumaGen-II (Randomized and Clinical Effectiveness Trial Comparing Two Pharmacogenetic Algorithms and Standard Care for Individualizing Warfarin Dosing), a randomized, blinded comparison of warfarin dosing using a one-step and three-step pharmacogenetic algorithm, and a clinical effectiveness comparison of the two pharmacogenetic algorithms with standard dosing in a parallel control group. Same-day results were obtained for genotyping of the CYP2C9 and VKORC1 genes, for incorporation into the pharmacogenetics dosing algorithms. The primary outcomes were percentage of out of range international normalized ratio (INR) test results at 1 and 3 months, and the percentage of time in therapeutic range (TTR) at 1 and 3 months. Primary analysis was done by the modified intention-to-treat method.


There were 245 subjects in the one-step algorithm group, 232 and the three-step algorithm group, for a combined total of 477 in the pharmacogenetics combined group. There were 1,866 parallel control patients. The pharmacogenetic three-step algorithm was noninferior to the one-step algorithm, but not superior for percentage of out of range INR at 1 month and 3 months, as well as for percentage of TTR of treatments. The combined pharmacogenetic cohort was superior to the parallel control group for percentage of out of range INR (31% vs. 42% at 1 month, 30% vs. 42% at 3 months; p < 0.001). The pharmacogenetics cohort was also superior to the parallel controls for the endpoint of percentage of TTR (69% vs. 58% at 1 month; 71% vs. 59% at 3 months; p < 0.001).


The authors concluded that pharmacogenetic dosing should be considered for broader clinical application, a proposal that is being tested further in three major randomized trials. The authors further opined that the simpler one-step pharmacogenetic algorithm provided equivalent results to a more complicated algorithm, and may be preferable for clinical application.


This study attempted to determine if more patient-specific information in the form of genetic testing leads to better clinical warfarin dosing. Prior small clinical trials have suggested this is not the case, as the standard approach to dose adjustment based on INR testing resulted in similar therapeutic efficacy. These studies may have been underpowered, however. The current study suggests that the pharmacogenetic algorithms tested resulted in statistically fewer out of range of INR test results, and more TTR, at 1 and 3 months. Several questions remain, however. First, is it feasible to use genetic testing in routine dosing of warfarin and existing clinical care settings, without incurring unreasonable expense? (Or for that matter, is it feasible to use an algorithm that algebraically computes 19 potential factors to determine dose?) Second, are the differences in TTR and number of out of range INR test results seen in this study clinically relevant? That is, is there any difference in bleeding or thrombotic outcomes? For the time being, it remains unclear how and when pharmacogenetic testing should be incorporated into the routine clinical care of patients receiving warfarin. The results of four large randomized trials currently underway may provide greater clarity.

Clinical Topics: Anticoagulation Management

Keywords: Antipsychotic Agents, Cardiology, Warfarin, Cardiovascular Diseases, Genetic Testing, Hemorrhage, Clozapine

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