Anticoagulation Flashcards
Who needs anticoagulation?
Atrial fibrillation Mechanical heart valves Tissue heart valves 3 months Cardiomyopathy MI (Anterior MI with LV dysfunction) Coagulopathy DVT and prophylaxis of venous thrombosis in high risk surgery Pulmonary Emboli Post op orthopedics
Virchow’s Triad
Hypercoagulable State
Endothelial Injury
Circulatory Stasis
Prothrombin Time
Needed to measure extrinsic pathway
Historically, a most reliable and “relied upon” clinical test
However:
Proliferation of thromboplastin reagents with widely varying sensitivities to reduced levels of vitamin K-dependent clotting factors has occurred
Concept of correct “intensity” of anticoagulant therapy has changed significantly (low intensity)
Problem addressed by use of INR (International Normalized Ratio)
Partial Thromboplastin Time/Activated Partial Thromboplastin Time (PTT or aPTT)
Needed to measure intrinsic pathway
PTT-Used as part of an investigation of a bleeding or thrombotic episode; to monitor unfractionated (standard) heparin anticoagulant therapy
This test measures the integrity of the intrinsic pathways of coagulation
The aPTT now measures the clotting time of plasma, from the activation of factor XII by a reagent (a negatively charged activator such as silica and a phospholipid) through the formation of a fibrin clot.
aPTT has replaced PTT, basically the same thing.
International Normalized Ratio
ratio calculated from the PT
The INR is calculated from the PT and is intended to allow valid comparisons of results regardless of the type of PT reagent used among different laboratories (INR = [patient PT / mean normal PT]).
The INR is a method of standardizing the PT for coumadin anticoagulation. Before the INR, different labs using different reagents had different controls and widely differing PT value ranges.
An INR of 1 means the blood clots “normally” for that pt. The greater the INR, the longer it takes the blood to clot.
Drugs that Decrease INR
American Ginseng (No effect on Warfarin with Asian Ginseng) Barbiturates Binding Resins Tegretol Oral Contraceptives PCN Rifampin St. Johns Wort Vitamin K
Drugs that Increase INR
Acetaminophen Alcohol Amiodarone Anabolic Steroids Antifungal Medications Aspirin Cephalosporin Chloral Hydrate Cimetidine Cranberry Juice Clofibrate Danazol Diflunisal Disulfram –anabuse Fluvoxamine Ginkgo Biloba Heparin HMG CoA Reductase inhibitors INH Macrolides Metronidazole Nalidixic Acid NSAIDS Paroxetine Penicillin Proafenone Quinidine Quinolones Sulfinpyrazone (Anturane) Tamoxifen Tetracycline Thyroid Hormone Trimethoprim-Sulfamethoxazole Vitamin E
Prolonged APTT in Non-heparinized individuals
Salicylates Inherited or acquired intrinsic clotting factor deficiency or abnormality (XII, XI, X, IX, VII, V, II, I) Massive blood replacement Hemophilia A Lupus anticoagulant Excessive coumadin dosage
Causes of Decreased APTT
Digitalis Tetracyclines Antihistamines Nicotine Elevated factor VIII Tissue inflammation or trauma
Bleeding Time
It addresses how well platelets interact with blood vessel walls to form blood clots following a wound or trauma.
A prolonged BT may indicate a vascular defect, a platelet function defect or thrombocytopenia.
The normal range can vary depending on the method used but is typically between 2 and 9 minutes.
BT is longer in women and in persons over 50 years of age.
Causes of a Prolonged Bleeding Time
Thrombocytopenia Disseminated intravascular coagulation Functional platelet disorders Capillary wall abnormalities Von Williebrand disease Medications: dextran, indomethacin, and salicylates (including aspirin).
Antidote for Coumadin
Vitamin K Onset 6-8 hours Dose/Routes of Administration 1mg IV (allergic reactions common) 1mg subcut (may delay onset) 1 mg po ( you can use the IV solution)
Antidote for Heparim
Protamine Sulfate
Warfarin Indications
Prophylaxis of venous thrombosis (high-risk surgery)
Treatment of venous thrombosis
Treatment of PE
Prevention of systemic embolism
Tissue heart valves
AMI (to prevent systemic embolism)
Atrial fibrillation
Mechanical prosthetic valves (high risk)
Certain patients with thrombosis and the anti-phospholipid syndrome
AMI (to prevent recurrent AMI)
Bileaflet mechanical valve in aortic position, NSR
Starting Warfarin
Loading dose for Warfarin is not needed
Indications for starting with concurrent Heparin
Thrombophilic state (e.g. known protein C deficiency)
Thromboembolism
Indications for starting Warfarin without Heparin
Chronic stable A Fib
Starting dose of Warfarin Usual: 5 mg PO qd (anticipate therapeutic by day 4-5) High Dose: 7.5 to 10 mg qd If urgency to reach therapeutic level Study: 10 mg start was therapeutic 1.4 days earlier Low dose: 2.5 mg PO qd Elderly Liver disease High risk of bleeding
