Time course of reversal of anticoagulant effect of warfarin by intravenous and subcutaneous phytonadione.
BACKGROUND
Excessive anticoagulation increases the risk of hemorrhagic complications associated with oral anticoagulant therapy. Oral or parenteral phytonadione is used to reverse excessive anticoagulation. Intravenous (IV) phytonadione, while effective, is associated with a small risk of serious anaphylactic reactions. Subcutaneous (SC) administration is safer, but there is little information on its relative efficacy in small doses.


METHODS
Twenty-two patients with asymptomatic prolongation of prothrombin time were prospectively randomized and treated with 1 mg of phytonadione IV or 1 mg SC. Prothrombin time was measured at baseline and at 8 and 24 hours after phytonadione administration and expressed as international normalized ratio (INR).


RESULTS
Mean INR at baseline was 8.0 and 8.5 in the IV and SC groups, respectively (P = .70). At 8 hours, mean INR was 4.6 in the IV group and 8.0 in the SC group (P = .006), and at 24 hours, mean INR was 3.1 in the IV group and 5.0 in the SC group (P = .009). Mean decrease in INR 8 hours after administration of phytonadione was 3.4 in the IV group and 0.4 in the SC group (P = .02), and mean decrease in INR after 24 hours was 4.9 in the IV group and 3.4 in the SC group (P = .18).


CONCLUSIONS
For patients who are excessively anticoagulated with warfarin, small doses of SC phytonadione may not correct the INR as rapidly or as effectively as when administered IV. Higher doses must be considered for more rapid and complete reversal of anticoagulation by the SC route.
Raj
G
G
Section of General Internal Medicine, Dallas Veterans Affairs Medical Center, and Department of Medicine, University of Texas Southwestern Medical Center, 75216, USA. raj.guna@dallas.va.gov
Kumar
R
R
McKinney
W P
WP
D000925:Anticoagulants / Q000037:antagonists & inhibitors* / Q000627:therapeutic use; D000933:Antifibrinolytic Agents / Q000008:administration & dosage* / Q000627:therapeutic use; D006801:Humans; D007275:Injections, Intravenous; D007279:Injections, Subcutaneous; D011446:Prospective Studies; D011517:Prothrombin Time; D016037:Single-Blind Method; D013997:Time Factors; D010837:Vitamin K 1 / Q000008:administration & dosage* / Q000627:therapeutic use; D014859:Warfarin / Q000037:antagonists & inhibitors* / Q000627:therapeutic use
D000925:Anticoagulants; D000933:Antifibrinolytic Agents; D014859:Warfarin; D010837:Vitamin K 1