Orthopaedic Jobs

Warfarin (Coumadin)


- Action:
      - inhibits Vit K dependent production of clotting factors
      - mainly inhibits prothrombin (II) and VII but also IX and X
      - 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

The use of novel oral anticoagulants for thromboprophylaxis after elective major orthopedic surgery.

Prevention of venous thromboembolic disease after total hip and knee arthroplasty.



Original Text by Clifford R. Wheeless, III, MD.

Last updated by Data Trace Staff on Tuesday, September 20, 2016 5:27 am