Genetics of warfarin dosing--one polymorphism at a time

Personalised Medicine: The Odyssey from Hope to Practice

In this endeavour, inspired by the Odyssey, we aim to embark with the reader on a journey on a ship from Troy to Ithaca, coursing through the history of the momentous events and achievements that paved the way for personalised medicine. We will set sail amidst important genetic discoveries, beginning with the discovery of the first human genome, and voyage through the projects that contributed to the progress of pharmacogenomic studies. Concurrently, we will propose methods to overcome the obstacles that are slowing the potential full implementation of accumulated knowledge into everyday practice. This journey aims to reflect on the frontiers of current genetic knowledge and the practical use of this knowledge in preventive, diagnostic and pharmacogenomic approaches to directly impact the socio-economic aspects of public health.

Optimization of vitamin K antagonist drug dose finding by replacement of the international normalized ratio by a bidirectional factor: validation of a new algorithm

ESSENTIALS: We developed a new algorithm to optimize vitamin K antagonist dose finding. Validation was by comparing actual dosing to algorithm predictions. Predicted and actual dosing of well performing centers were highly associated. The method is promising and should be tested in a randomized trial.

SUMMARY

BACKGROUND

Oral vitamin K antagonists (VKAs) have a narrow therapeutic window and thus require frequent monitoring of its intensity by the international normalized ratio (INR). Improvement of VKA dosing defined as more time in therapeutic range (TTR) can reduce thrombotic disease and bleeding. Computerized decision support programs (CDSs) are used to optimize VKA dosing, but the effects are heterogeneous. CDSs significantly improve the proportion of time in the therapeutic INR range for initiation therapy but not the quality of anticoagulant management in an outpatient setting. One of the major problems of VKA dose finding is that the INR is a ratio and does not present linearity. We developed a new dose-finding algorithm, based on a novel bidirectional factor (BF). This BF is linear transformation of the nonlinear INR.

METHODS

We compared the outcomes of the new algorithm, called BF-N, with dose finding performed at three highly ranked Dutch anticoagulation centers, using both acenocoumarol and phenprocoumon.

RESULTS

The outcomes of the BF-N algorithm showed a linear correlation with VKA doses of the three centers (y = 1.001x, r(2) 0.999 for acenocoumarol and y = 0.999x, r(2) 0.999 for phenprocoumon), with a standard deviation of 3.83%. The rate of automated dosage proposals increased to 100%.

CONCLUSION

The BF-N algorithm performs well in real-life settings and increases the rate of automated dosage proposals. The algorithm can be easily built into existing CDSs. Experienced staff remains necessary for complicated situations. The new algorithm needs to be evaluated in a prospective trial.

Genotype-Guided Dosing of Coumarin Anticoagulants

Background:

Coumarin anticoagulants (acenocoumarol, phenprocoumon, and warfarin) are generally used for the prevention of stroke in patients with atrial fibrillation or for the therapy and prevention of venous thromboembolism. However, the safe use of coumarin anticoagulants is restricted by a narrow therapeutic window and large interindividual dosing variations. Some studies found that the effectiveness and safety of coumarin anticoagulants therapy were increased by pharmacogenetic-guided dosing algorithms, while others found no significant effect of genotype-guided therapy.

Methods:

Four electronic databases were searched from January 1, 2000, to March 1, 2014, for randomized controlled trials of patients who received coumarin anticoagulants according to genotype-guided dosing algorithms. The primary outcome was the percentage of time that the international normalized ratio (INR) was within the normal range (2.0-3.0). Secondary outcomes included major bleeding events, thromboembolic events, and INR ≥4 events.

Results:

Eight studies satisfied the inclusion and exclusion criteria. Genotype-guided dosing of coumarin anticoagulants improved the percentage of time within the therapeutic INR range (95% confidence interval [CI], 0.02-0.28; P = .02; I2 = 70%). Subgroup analysis was performed after dividing the nongenotype-guided group into a standard-dose group (95% CI, 0.14-0.49; P = .0004; I2 = 50%) and a clinical variables-guided dosing algorithm group (95% CI, −0.07-0.15; P = .48; I2 = 34%). There is a statistically significant reduction in numbers of secondary outcomes (INR ≥4 events, major bleeding events, and thromboembolic events; 95% CI, 0.79-1.00; P = .04). Subgroup analysis of secondary outcomes showed no significant difference between genotype-guided dosing and clinical variables-guided dosing (95% CI, 0.84-1.10; P = .57; I2 = 11%), but genotype-guided dosing reduced secondary outcomes compared with standard dosing (95% CI, 0.62-0.92; P = .006; I2 = 0%).

Conclusions:

This meta-analysis showed that genotype-guided dosing increased the effectiveness and safety of coumarin therapy compared with standard dosing but did not have advantages compared with clinical variables-guided dosing.

Drug adherence in patients taking oral anticoagulation therapy

Oral anticoagulation has proven to reduce mortality and morbidity of thromboembolic events. One of the most important determinants of the effectiveness and safety of anticoagulation therapy is the adherence to the prescribed therapy. Vitamin K antagonists are characterized by under-utilization, a narrow therapeutic window and multiple food and drug interactions which contribute to a variable dose-response relationship with the risk of insufficient protection and/or increased bleeding risk. The "new" direct oral anticoagulants have demonstrated equal or superior protection and reduced bleeding risks compared to warfarin and are easier to use because of fixed dosing without monitoring of anticoagulation. Controlling of adherence to the direct oral anticoagulants is difficult. Therefore, continuous and regular medication intake represents a pre-requisite for achieving optimal protection. The present review aims to give an overview about the factors that affect drug adherence in patients taking oral anticoagulation drugs and discusses strategies to improve drug adherence.