Summary.The optimal management of asymptomatic overanticoagulated patients remains unknown. We measured international normalized ratio (INR), activated partial thromboplastin time (APTT) and prothrombin fragment 1 1 2 (F1 1 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.
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