As an alternative anticoagulant other than warfarin, new oral anticoagulant (NOAC) has been used in clinical practice for a long time. Therefore, the “New” has been replaced by “Direct”, and “NOAC” has been renamed as “DOAC”. Compared with warfarin, the prescription of DOAC increases rapidly because its effectiveness and administration convenience.
On the other hand, unlike warfarin, DOAC has no effect index, and the dose reduction standard has been established when the standard dose should be reduced in view of patients’ condition.
According to the summarization till 2015 in Fushimi AF Registry1 The percentage of cases that conform to the dose reduction standard is about 63% among all patients. However, 39%‐59% cases with dose reduction received inappropriate dose reduction. Furthermore, based on the report of ORBIT‐AF II, 16% cases received dosage reduction but 57% of them were not the indicators of dosage reduction. The latter group had a larger stroke rate, and a larger bleeding rate with unknown reasons. It is also reported that compared with those whose NOAC dose was appropriately reduced, patients receiving inappropriate dose reductions were younger (median age 79 vs 84, P < .0001) and had lower ORBIT bleeding risk scores (26% ≥4% vs 45%, P < .0001)2 In view of the above results, we should carefully ponder the dose of DOAC.
In Japan, doctors usually carefully consider the prescription dose. In clinical practice, they usually consider dose reduction in case of bleeding tendency and possible bleeding.
Nevertheless, even when patients receive inappropriate dose reduction, the possibility of bleeding is not zero because of their bleeding tendency, and stroke may also happen. However, the results of ORBIT‐AF II are contradictive. For younger age and low bleeding risk groups, the dose reduction percentages were 63% in Japan and 16% in ORBIT‐AF II. There is a large difference. In addition, the younger group was composed of cases at the age of 79‐84 years old in ORBIT‐AF II. These cases are regarded as seniors in Japan. In view of the difference of basic diseases, the two results cannot be compared directly.
Currently, the dose reduction standard of DOAC is based on age, weight, kidney functions, and so on. These indexes change with time and are not fixed at all. In addition, INR, as an index of warfarin, has a racial difference. The effect of DOAC may also have a racial difference.
Furthermore, many DOAC have not only anticoagulant effect but also antithrombotic effect. The mechanism may ascribe to fibrin dissolution of platelet set but the pharmacological effect is unknown. Therefore, DOAC has many mysteries to be resolved.
It is urgent to confirm the safe standard for the usage of DOAC. Therefore, it is important to confirm related issues based on clinical results like this manuscript.
CONFLICT OF INTEREST
The authors declare no conflict of interests for this article.
REFERENCES
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