Oral Anticoagulants Flashcards
What are the oral anticoagulants?
Warfarin (coumadin), Dabigatran (Pradaxa), Rivaroxaban (Xarelto), Apixaban (Eliquis)
Warfarin MOA
Reversibly binds and inhibits enzymes which converts inactive vit K to active vit K, decreases production of vit K-dependent clotting factors; decreases production of natural anticoagulants protein C and S
Warfarin (Coumadin) facts
racemic mixture, well absorbed (100%) highly protein bound to albumin, average T1/2: 36-42 hours
Warfarin (Coumadin) monitoring
Done with INR, responsive to depression of factors II, VII and X; initial prolongation due to factor VII, antithrombotic effect requires 5-7 days of treatment
Challenges associated with warfarin
Drug interactions, frequent monitoring, food interactions, genetic variances in metabolism, narrow therapeutic index, disease state interactions, long/variable half-life, stigmas
Factors that increase the effects of warfarin
hyperthyroidism, fever, liver disease, acute heart failure, diarrhea/vominting, genetics
Factors that decrease the effects of warfarin
hypothyroidism, fat malabsorption, genetics
Drug interactions of warfarin that increases effect
ciprofloxacin, bactrim, alcohol, citalopram, fish oil, propranolol etc
Drug interactions of warfarin that decrease effect
griseofulvin, ribavirin, rifampin, mesalamine, barbiturates, high vit K foods
Clinical uses of warfarin
prevention of stroke in patients with afib, VTE, history of stroke, VTE prophylaxis
Exception to goal 2-3 INR in pt taking warfarin
pt with mechanical valves, goal is slightly higher
What is bridge therapy
treating patients with concurrent anticoagulants to bridge the gap between when the warfarin is initiated and when it is therapeutic
What is most common drug used with bridge therapy
enoxaparin
Pros of early therapeutic INR
decreased length hospital stay, decreased cost of and exposure to using injectable anticoagulants
Cons of early therapeutic INR
risk of bleeding, increased hospital stay and cost, clouded picture of patient’s maintenance dose
Risk factors for bleeding
patient older than 75 yo, bleeding history, serious comorbid conditions, HTN, CVD
When to obtain INR
after 2-3 doses of warfarin and then daily until therapeutic INR reached, outpatient reduce initial monitoring to every few days until a therapeutic dose
Initiating warfarin
start 5-10 mg for first 1-2 days, subsequent dosing based on INR response, do not load doses
When to start doses lower than 5 mg
in patients with increased risk of bleeding, elderly, debilitated, malnourished, CHF, liver disease
Monitor using
INR, PT, PTT
what is used to reverse anticoagulation with decreased vitamin K
phytonadione
Vitamin K recommendations
INR9 5 mg PO, INR >20 or serious bleeding 10 mg IVPB, if no signs or symptoms of bleeding do not treat
Dabigatran (Pradaxa)
Oral direct thrombin inhibitor, must adjust for renal, very fast onset (6hrs) so no bridge needed, no monitoring required, no antidote for bleeding, some DI
Clinical uses of dabigatran (Pradaxa)
prevention of stroke and systemic emboli in nonvalvular Afib, treatment of VTE (requires 5-10 days of parenteral anticoagulation
