Warfarin Flashcards
Advantages of DOACs
Wide therapeutic window - allows for fixed dosing without need for routine AC monitoring
Rapid onset - no initial treatment needed with IV AC
Predictable
No food interactions
More convenience for patients and providersW
Warfarin
-half life
-monitoring
-MOA
-pharmacokinetics
-CI
-colours
T1/2 - 40hrs
-loading doses needed to achieve steady state quickly
INR
If INR too high, and asymptomatic - omit dose and recheck INR
-if INR 8+ => VitK 5mg (low dose) to avoid full reversal and temporary resistance to warfarin
VKA - inhibit VitK epoxide reductase => inh synthesis of VitK dependent clotting factors (1972)
Liver metabolism - CYP2C9 (metabolises most potent enantiomer)
CI
Current significant bleed/high bleed risk
-stroke, hemorrhage
-bleeding disorders
-U75 platelets
Decompensated liver disease
Physiological
-pregnancy 1st-3rd trimester
-U48hrs postpartum
Medications
-St John’s Wort - reduced VKA
Nonadherence - cognitive impairment
White - 500mcg
Brown - 1mg
Blue - 3mg
Pink - 5mg
AC
-prophylaxis indications
-treatment
Primary/secondary prevention of thromboembolus from
-valve disease
-prosthetic/mechanical valves
-AF, flutter
Prevention after
-orthopedic surgery
-bariatric surgery
-cancer surgery
-lower limb immobilisation
-pregnant/postpartum patients at risk of VTE
Prevention for recurrent VTE
PE, DVT
Duration of treatment for
-heart valves
Mechanical - lifelong
Tissue - PO AC short duration and/or AP
DOACs not indicated for valvular heart disease/AF
VTE treatment
-provoked - 3 months
-unprovoked - 6 months
VTE prevention
-high risk surgical - continue for 28days postop
-lower limb immobilisation - for duration of immobilisation
-pregnant - antenatal and 6wks postnatal
AF
-balance of CHADSVASC and ORBIT
Type of
-PO AC
-IV AC
VKA
-warfarin
-acenocoumarol
-pheninodione
DOAC
-apixaban
-edoxaban
-rivaroxaban
-dabigatran
Heparins
-enox
-unfractionated
Fondaparinux - inh activated X
-used for unstable angina/NSTEMI where PCI not indicated
-HIT
Cautions for warfarin
Bleeding
-acquired
-Hx of GI bleeds
-risk factos
-uncontrolled HTN
Medical
-Acute IE
-Alcoholism
65+
Medications that increase bleeding risk
-AC
-NSAIDs
-SSRI
-SSNI
-AP
Warfarin adverse effects
Easy bleeds, bruises
Hemorrhage
Hematemesis
Hemarthrosis
Hematuria
Severe bruises
Severe headaches
Warfarin induced skin necrosis
Warfarin
-management
-monitoring - how
-monitoring - frequency
-target
New patients on VKA therapy => referred to AC clinic for monitoring
INR - measure how floody blood is
-capillary and peripheral samples will differ slightly
Initiation - INR, FBC, LFT, U&E, coagulation
Frequent monitoring needed if
-rapid loading
-drug interactions likely - 3-7 days after new med started or stopped
-comorbidities
-change in dose
Target generally - 2-3
-Aortic valve - 2.5-3.0
-Mitral valve - 3.0-3.5
Warfarin drug drug interactions
-increased INR
-decreased INR
-increased INR from non drugs
-decreased INR from non drugs
Increase
Antiarrythmics
ABx - pens, fluoroquinolone, macrolides, tetracyclines trimethoprim
Antidepressants - SSRI, SNRI, TCA
Antiplatelets
Azoles
CS
Statins
NSAIDs
Thyroid hormones
PPIs
Decreased
Rifampicin
AEDs
St Johns Wort
Increase INR
Alcohol
Cranberry juice
Grapefruit juice
Decrease INR
Leafy greens
Managing raised INR
Omit or reduce VKA dose
Reverse AC if clinically indicated
Investigate cause
Risk vs benefit of continuing treatment
Emergency AC reversal if major bleed
-25-50U/kg prothrombin complex
-5-10mg IV VitK
Perioperative AC use
Minor procedure - continue if INR stable
Invasive procedure - stop 5 days before
-bridging therapy with enox until INR in therapeutic range for 2 consecutive days
