A Brief Synopsis of "Updated Guidelines on Outpatient Anticoagulation" from AFP

 A brief synopsis of "Updated Guidelines on Outpatient Anticoagulation"
PATRICIA WIGLE, PharmD, BCPS, and BRADLEY HEIN, PharmD, University of Cincinnati James L. Winkle ,College of Pharmacy, Cincinnati, Ohio, HANNA E. BLOOMFIELD, MD, MPH, University of Minnesota and Minneapolis VA Medical Center, Minneapolis, Minnesota, MATTHEW TUBB, MD, PhD, The Christ Hospital/University of Cincinnati Family Medicine Residency Program, Cincinnati, Ohio, MICHAEL DOHERTY, PharmD, BCACP, University of Cincinnati James L. Winkle College of Pharmacy, Cincinnati, Ohio

http://www.aafp.org/afp/2013/0415/p556.pdf
Am Fam Physician. 2013 Apr 15;87(8):556-566.

This is a very detailed article (see how many authors!)  that i reviewed and I suggest reading it for more information
     For many decades, warfarin was the only option for anticoagulation, besides aspirin.  Recently, newer medications have come on the market.
     Warfarin is an anticoagulant which inhibits vitamin K dependent clotting factors II, VII, IX, and X. Due to the half life of these clotting factors, warfarin can take several days to take effect. In the beginning stages of using this drug, there is a paradoxical increase in clotting risk due to the decrease in protein C and S. Heparin or LMWH is used at the onset of warfarin therapy due to this hypercoagulable state. It is continued until the INR is in therapeutic range for 24 hours. Heparin is eventually stopped and warfarin is used because warfarin is an oral medication and heparin is not.
     Warfarin can be started at 5-10 mg per day and then adjusted, depending on the INR. If it is elevated, but less than 4.5, the dosage can be lowered or held. With levels 4.5 to 10, one or two doses should be held, then resumed at a lower dosage once the INR is therapeutic.  If the INR is greater than 10, the patient may need vitamin K, in addition to holding the medication, to reverse the effects of warfarin. There are many drug and food interactions that can affect the effects of warfarin.  Amiodarone and rifampin, for example, can alter the INR long after the medication has been discontinued. Diet should be maintained while using warfarin  without and drastic changes, such as becoming a vegan.
     Unfractionated heparin works by inactivating factor IIa and Xa by binding to antithrombin. It also prevents the growth of clots. There is a risk of bleeding with this drug as well as an increased risk in HIT.
     The two LMWHs are lovenox and fragmin. It is given subcutaneously. Anti-factor Xa monitoring is not needed. Bleeding and HIT can be an issue, although less likely than unfractionated heparin.
     Fondaparinux is a synthetic analogue of heparin. It had no effect on thrombin formation and only works on factor Xa. It is given subcutaneously as well and does not need to be monitored.
     There are times when anticoagulation needs to be stopped. According to this article, if the patient is to have surgery, warfarin can be stopped 5 days before the procedure and restarted one to two days after. If there is only a low risk of bleeding, perioperative bridging may not be indicated. Otherwise it may be necessary to bridge the patient with LMWH or unfractionated heparin during the perioperative period.
     The biggest issue with warfarin is getting the dosage right, and the constant need for adjusting it. The advent of newer meds is very appealing, due to its ease of prescribing and lack of need for monitoring. Dabigatran is an anticoagulant that is effective in preventing embolism and stroke for patients with nonvalvular atrial fibrillation. Rivaroxaban is effective in prevention of DVT in patients having hip or knee replacement surgery, in treatment of DVT and PE, and prevention of embolism in nonvalvular atrial fibrillation.