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warfarin therapy

warfarin indication prevention or treatment of thromboembolism
conditions for warfarin use VTE, A fib, stroke, mechanical heart valves
usual starting dose of warfarin 5mg po qd (2.5-10mg range)
start lower dose if pt over 65y/o, abnormal liver fxn, malnourished, low vitamin K intake, recent surgery, medications inducing warfarin
subsequent warfarin dosing based on INR
normal PT 10-13seconds
INR reference 1
goal INR normally 2.0-3.0
goal INR mechanical valves 2.5-3.5
goal INR prior to surgery <1.5
INR monitoring: inpatient every 1-3 days
INR monitoring: outpatient within 3-5 days every 4 weeks once stable
warfarin monitoring BLEEDING s/sx of thrombus
warfarin adverse effects bleeding, alopecia, cold intolerance, skin necrosis, purple toe syndrome, rash, jaundice, vertebral and rib fractures
warfarin metabolism CYP3A4 and CYP2C9
warfarin in hypothyroidism increase dose
warfarin in hyperthyroidism decrease dose
hypothyroid more likely to clot
hyperthyroid more likely to bleed
warfarin inducers alcoholic grizly dic nabed (a) car (to) run phen phen
warfarin inhibitors bac met ami (and) left the sorority assholes (to) make icy flowers sometimes
platelet fxn inhibitors ASA NSAIDS, COX II inhibitors, acute alcohol
reduce GI flora synt of vitamin k antibiotics
reduce GI absorption cholestyramine, sucralfate
change protein binding leflunamide, bactrim, alcohol
APAP limit to <2g daily and short term
OTC warfarin interactions boost, one a day (vit K) alka seltzer (ASA)
how much vitamin K to change INR 1 IU? 714mcg weekly
herbals that inc. INR garlic, ginger, chondroitin, glucosamine, horse chestnut, milk thistle, saw pamento, flax seed, fish oil
herbals that dec. INR CoQ10, st. john's wort, green or herbal teas
herbals that are unpredictable on INR ginseng
if adding warfarin to regimen titrate to desired INR
adding if warfarin is already part of regimen may see large fluctuations in INR so monitor it closely
long term/short term offender use stabalize INR/monitor without dose change
when to check INR followin initiation or discontinuation of a drug 3 days following
warfarin with inducer increase warfarin dose
warfarin with inhibitor decrease warfarin dose
dietary vitamin K sources green vegetables, mayo, oils, soymilk,boost type deals
inpatient subtheraputic INR give 1 additional "booster" dose *do not change weekly maintenance dose
outpatient subtheraputic INR increase by fraction of weekly dose (10-20%) check for transient factors
inpatient supratheraputic INR hold one dose adjust daily warfarin dose
outpatient supratheraputic INR hold at least one dose decrease weekly dose (10-20%)
CHEST recommendations INR 3.0-5.0 if no bleeding, hold dose(s) decrease weekly dose by 0-10% -if transient factor no dose reduction
CHEST recommendations INR >5.0-9.0 if no bleeding, hold dose(s) decrease weekly dose by 10-20% can consider po vit.K 1mg - 2.5mg if at high risk for bleeding
CHEST recommendations INR >9.0 if no bleeding, hold dose(s) give po vit.K 2.5-5mg, reduce dose of warfarin once restarted
serious supratheraputic INR and bleed hold warfarin, IV vit.K 10mg by slow infusion supplement with frozen plasma, prothrombin complex, or recombinant factor VIIa repeat vit.K in 12 hours if persisten elevated INR
vitamin K, Phytonadione (mephyton) vit. k for clotting factors
vit.K oral route onset 6-12 hours INR theraputic in 24-48 hours
vit.K IV route onset 1-2 hours control of hemorrhage evident in 3-6 hours
vit.K IV or >5mg po leads to overcorrection and warfarin resistance lasting up to a week
never administer warfarin IM never administer warfarin IM
Created by: lex86