A prospective randomized study to determine the optimal dose of intravenous vitamin K in reversal of over‐warfarinization

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Abstract
The optimal management of asymptomatic overanticoagulated patients remains unknown. We measured international normalized ratio (INR), activated partial thromboplastin time (APTT) and prothrombin fragment 1 + 2 (F1 + 2) over 7 d in 24 asymptomatic or mildly haemorrhagic patients on warfarin with prolonged INR of > 7·0 who were randomized to receive 0·5 mg, 1 mg or 2 mg intravenous vitamin K. Of six severely overanticoagulated patients (INR > 9·5 with APTT ratio > 2), five failed to achieve an INR ≤ 4·0 on day 1, irrespective of vitamin K dose given. In the remaining 18 cases, an optimal response (INR 2–4 at day 1) was observed in 67% of those receiving 0·5 mg vitamin K, but only in 33% of those receiving 1 or 2 mg, the majority of whom developed an INR < 2·0. Our results support an optimal dose of 0·5 mg i.v. vitamin K for most overanticoagulated patients, with possibly a repeat dose in the small group of severely overanticoagulated patients.