Dosage and control of oral anticoagulants: an international collaborative survey

An international survey of oral anticoagulant dosage has been carried out comparing the mean dosage prescribed in hospitals in 23 countries. In addition, participants using the Quick prothrombin time test were asked to assess the adequacy of dosage of a lyophilized test plasma which was mid-therapeutic using the British Comparative Thromboplastin (BCT). The overall mean dosage proved similar for the groups of laboratories using the Quick test and human brain thromboplastin and Thrombotest although wide differences existed between individual centres. The survey indicated that these discrepancies were due partly to the adoption of different intensities of anticoagulation. In addition, local differences in patients' response to anticoagulants were apparent, e.g. North American centres prescribed a higher mean dose with a more intense therapeutic range than Europeans. Hong Kong physicians appear to prescribe a much lower dose than the rest of the world although the intensity of their treatment is comparable, whereas South African hospitals give moderate doses of warfarin despite a conservative therapeutic range. Such geographical variation in response would invalidate standardization of anticoagulant treatment based on the mean dosage approach.