- Action:
- inhibits
Vit K dependent production of
clotting factors
-
VII (t/2=4-6hrs),
IX (t/2=18-24hrs),
X (t/2=18-24hrs),
II (t/2=18-24)
- proteins C (t/2=6 hrs) and S (early);
- hence
PT increases in 48 hrs 2nd to decr of VII but many days of therapy needed for therapuetic levels of other the factors;
- Dose:
- usually given within 3 days of
heparin therapy;
- loading Dose: 5-15 PO/IM/IV qd for 1-5 days;
- maintenance: 2-15mgPO/IM/IV;
- supplied: 1.0, 2, 2.5, 5, 7.5, 10mg;
- Labs:
- titrate dose keeping PT = 1.2-1.5 x normal;
- initially check PT
PT & PTT qd; PT incr. in less than 48 hrs;
- expect therapuetic PT in 5-6 days; Then check PT q1-2 weeks;
- Precautions:
-
warfarin induced skin necrosis:
- be careful with patients w/ elevated platlet levels;
-
warfarin interactions and resistance:
- avoid
ASA and IM injections;
- acetaminophren may interfere with hepatic metabolism of warfarin (and thus may increase INR);
- note that
Vit K 10-50mg SC/IM or for rapid (but expensive) correction may use
FFP (2 units at a time) / check PT;
- for Prolonged Reversal of Anticoag:
Vit K 10 mg PO/SC/IV for 3 days;
References
New Anticoagulants — The Path from Discovery to Clinical Practice
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