A WARFARIN INDUCTION REGIMEN FOR OUTPATIENT ANTICOAGULATION IN PATIENTS WITH ATRIAL-FIBRILLATION

Currently available protocols for induction of warfarin anticoagulatio n employ initial doses of 10 mg and are best suited to in-patient use. However, with the increasing number of elderly patients with atrial f ibrillation requiring anticoagulation, there is a need for a less inte nse regimen which could be used for out-patients. We have established such a regimen and report on its prospective evaluation in 37 patients referred for out-patient initiation of warfarin, and a non-randomized comparison with 37 inpatients, with similar diagnoses, commenced on a traditional warfarin protocol. After exclusion of five patients on am iodarone, all of whom experienced supratherapeutic International Norma lized Ratio (WR) results, the new outpatient regimen, employing an ini tial 5 mg dose, resulted in a lower maximum INR during the first 21 d therapy (median 2.9 v 4.0; P = 0.0001) and fewer INRs > 4.5 (2/36 v 9/ 33) compared to the traditional 10 mg regimen. Time to reach stable an ticoagulation was similar with each regimen; however the 5 mg regimen gave a more accurate prediction of maintenance dose (correlation coeff icient for predicted versus actual maintenance dose, r = 0.985). In co mparison to a traditional 10 mg protocol, the proposed 5 mg warfarin i nduction regimen proved both safer and more reliable for initiation of prophylactic anticoagulation in patients with atrial fibrillation.