Can warfarin randomized trials be reproduced in 'real life'? Adherence to warfarin guidelines for intensity of anticoagulation in a university-based warfarin clinic.

BACKGROUND: Subjects in clinical trials may benefit from the increased attention and specific focus of the trial, thereby limiting the external validity of clinical trial results to clinical practice. Our study evaluated adherence to guidelines for intensity of anticoagulation in a large, university-based warfarin clinic to assess the generalizability of randomized clinical trials of warfarin efficacy to clinical practice.
METHODS: We reviewed anticoagulation clinic records of 480 patients observed for up to 2 years to determine the amount of time anticoagulation was within the recommended therapeutic range.
RESULTS: The most common indication for warfarin use was atrial arrhythmia (51.5%). Overall, anticoagulation was within the intended international normalized ratio (INR) target range on 57.8% of treatment days. Nontherapeutic treatment days were due more commonly to subtherapeutic INR values (27.6+/-25.7%) than supratherapeutic INR values (14.9+/-17.0%). This pattern was seen across all warfarin indications.
CONCLUSION: These data are comparable to those reported from large randomized trials and thus support the generalizability of clinical trials of long-term warfarin anticoagulation to clinical practice.