What should target international normalised ratio be?

EDITOR—Factual errors require correction in English and Channer's editorial on managing atrial fibrillation in elderly patients.1 The authors state that the Boston area anticoagulation trial for atrial fibrillation and the stroke prevention in atrial fibrillation III (SPAF III) trial showed that anticoagulation to an international normalised ratio of 1.5-3.0 is safe and effective, referencing a 1994 review article to support this statement. The SPAF III trial was not published until 1996,2 so the reference is presumably to the SPAF II trial.3

The target for anticoagulation in the Boston area anticoagulation trial for atrial fibrillation was a prothrombin time ratio of 1.2-1.5 (corresponding roughly to an international normalised ratio of 2.0-3.0),4 whereas in the SPAF II trial it was a prothrombin time ratio of 1.3-1.8 (roughly an international normalised ratio of 2.0-4.5) The SPAF III trial showed that in high risk patients fixed dose warfarin (initial international normalised ratio 1.2-1.5) plus aspirin was less effective than adjusted dose warfarin (international normalised ratio 2.0-3.0). A subsequent trial of fixed dose warfarin was stopped early in the light of the results of the SPAF III trial. At stopping, there was a trend favouring adjusted dose warfarin.5

In patients with atrial fibrillation treated with warfarin, current evidence suggests that the best ratio of benefit to risk is achieved when the target …