Phytonadione Therapy in a Multiple-Drug Overdose Involving Warfarin

Duane Bates, B.Sc.(Pharm.), and Marcy Mintz, M.D.

Disclosures

Pharmacotherapy. 2000;20(10) 

In This Article

Discussion

A single dose of warfarin 0.5 mg/kg may prolong prothrombin time, and doses of 6-15 mg/kg have been fatal.[2] Our patient ingested 2.6 mg/kg of warfarin. Symptoms generally are delayed 1.5-3 days (range 1-7 days),[2] and usually involve coagulopathy with an elevated INR. Common initial symptoms include abnormal bruising, petechial rash, prolonged bleeding from minor cuts, epistaxis, gingival bleeding, hematuria, hematochezia, hemoptysis, hematemesis, and vaginal bleeding.[2] Severe hemorrhage may result in hypotension, shock, and death, and intracranial hemorrhage may result in neurologic deficits.[2]

It is recommended that for a warfarin overdose, the INR be measured once or twice/day for early detection of a coagulopathy.[2,3] It is necessary to monitor vital signs and hemoglobin levels as well as stool and urine for evidence of blood loss.[2] It is suggested that oral phytonadione 50-100 mg be given 3-4 times/day for 1-2 days.[3] The INR should be monitored, and the dosage of phytonadione adjusted accordingly. If severe bleeding occurs, it should be reversed with fresh-frozen plasma followed by intravenous vitamin K.[2,3] The minimum dose for adults is 10 mg, and some patients may require 25-50 mg.[2,3] The dose may be repeated every 6-8 hours as required.[2,3] The intravenous route is more effective than the subcutaneous route for terminating active bleeding.[1,4,5]

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