Anticoagulation Flashcards
Normal hemostasis steps
- small blood vessel injury
- vasospasm decreases blood flow
- platelets adhere and form a plug to stop bleeding
- coagulation activation–>fibrin clot
- after vessel is repaired, clot removed by fibronolysis
Virchow’s Triad
venous stasis
hypercoagulobility
vascular injury
Parenteral anticoagulants
unfractionated heparin (UFH/Heparin)
low molecular weight heparins (LMWH)
Mechanism of action of heparin
prevents the conversion of fibrinogen to fibrin, preventing further clotting
does not affect established thrombus
Indications of heparin
venous thromboembolism (DVT/PE) tx and prophylaxis
unstable angina
acute MI
coronary bypass surgery
hemodialysis
angioplasty
IV line flushes
Pharmacokinetics of heparin
Non-linear elimination of heparin: be careful with dosing because half life increases as dose increases
Adverse reactions of heparin
Hemorrhage
Heparin induced thrombocytopenia (HIT): platelets <100,000, need to discontinue heparin
Heparin associated thrombocytopenia (HAT): mild thrombocytopenia, manage by observation
Long term: osteoporosis and hyperkalemia
Antidote for heparin
protamine
Adverse Reactions
Hemorrhage
Thrombocytopenia and osteoporosis, but less than heparin
Types of oral anticoagulants
Warfarin
Dabigatran
Rivaroxaban
Apixaban
(Warfarin only one with antidote)
Mechanism of action of warfarin
Interferes with hepatic synthesis of vitamin K dependent clotting factors (Vit K antagonist)
Onset of effect 36-72 hours
Not thrombolytic
Indications to use warfarin
Venous thromboembolis (DVT/PE) treatment and prophylaxis
Prosthetic heart valves
A fib
TIA/Stroke
Acute MI
Hypercoagulable states
Peripheral arterial occlusive disease
Pharmacokinetics of warfarin
(Absorption, distribution, metabolism)
Absorption: Well absorbed in GI tract 99%
Distribution: >97% bound to plasma proteins, crosses placenta, but not breast milk
Metabolism: Half life is 1-2 days, longer in elderly with CHF exacerbation
Adverse reactions of warfarin
Hemorrhage
Skin necrosis (rare, discontinue drug and administer vitamin K)
Purple toe syndrome
CI and precautions of warfarin
Patients with addition risks of hemorrhage
Noncompliance with drug therapy or monitoring
Alcoholism
Surgery, dental work
Spinal anesthesia or injectons
Warfarin drug interactions
*Assume an interaction until proven otherwise!
metabolized by CYP450
Increase INR: sulfamethoxazole (Septra)
Increase bleeding risk, but don’t change INR: Aspirin and NSAIDs
Dietary considerations for warfarin
(food)
Make sure that vitamin K intake is consistent to stablize INR
Many supplements can affect platelet function and anticoagulation status–check
Alcohol effects on Warfarin
Acute intake: increase INR
Chronic intake: decrease INR (inc hepatic metabolism)
Cirrhosis: increase INR (can’t metabolize)
Anticoagulation recommendations for prevention of VTE
Vary depending on risk for VTE
- Heparin
- LMWH
- Fondaparinux
- Graduated compression stockings and/or intermittent pneumatic compression devices
Anticoagulation recommendations for treatment of VTE
Parenteral anticoagulant and warfarin
- Parenteral anticoagulant for 5-7 days (continuous infusion heparin OR subQ UFH, LMWH, or Fondaparinux)
- Warfarin therapy begins on day 1 after first dose of parenteral anticoagulant
- Overlap because heparin has long half life
- Must have therapeutic INR for 2 days before stopping heparin
Thrombolytics
- Not recommended for most patients because intracranial bleeding can occur
CHADS2
Congestive heart failure
Hypertension
Age >75yrs
DM
Stroke or TIA
Study of variability in hereditary factors as it relates to drug response in different populations
Pharmacogenetics definition
“Right Medicine for the Right Patient”
Warfarin Therapy and CYP2C9
CYP2C9 variants are associated with a different warfarin maintenanace dose, time to stable dose, above range INRs and bleeding events
Screening for CYP2C9 may help prescribers avoid overanticoagulating
Contraindications for Anticoagulation Therapy
Active bleeding
Hemophilia
Severe liver disease
Severe thrombocytopenia
Malignant HTN
Inability to meticulously supervise and monitor treatment
