Anticoagulation
therapy
Anticoagulant
drugs are conveniently divided into three main groups: orally active agents,
heparin and thrombolytic agents. Oral coagulants themselves comprise two groups:
the coumarins (warfarin, dicoumarol, nicoumalone, phenprocoumon and others) and
the indanediones (phenindione, anisindione and others).
Warfarin
sodium enjoys by far the most widespread clinical usage. presently the only
anticoagulants available for oral use.
These
compounds depress hepatic synthesis of the four vitamin K-dependente
procoagulants (factors II, VII, IX, and X) and of two inhibitors (protein C and
S).
The
indications for long term prophylactic treatment is thromboemboly.
Patients
receiving warfarin therapy should have frequent m
easurement of
anticoagulation and this should be performed using the International Normalized
Ratio (INR). Prothrombin time is no more indicated.
Thromboembolic risk
|
High, >
6% per year |
Medium, 2-6% |
Low, < 2% |
|
Acute
coronary syndrome Vein grafts
(1-3 months old) Coronary
intervention |
Stable
coronary artery disease Vein grafts
< 1 years old |
Primary
prevention of CAD |
|
Anticoagulant
+ platelet Inhibitor
(PI) |
Anticoagulant
+ PI |
PI |
|
Mitral
stenosis and Atrial fibrillation (AF) |
Non valvular AF,
anterior MI, LV disfunction |
Mitral
stenosis with normal rythm, Lone AF, Chronic LV aneurysm |
|
AF +
previous tromboembolism |
|
|
|
INR 2.5-3.5 |
INR 2-3 |
No therapy |
|
Old
prosthetic valve Prostetic
valve and previous thromboembolism |
Prosthetic
valve, bioprosthetic valve early Postoperatively
or with AF |
Bioprosthetic
valve and Normal Sinus Rhythm |
|
INR 3-4.5 or
INR 2.5-3.5 + ASA |
Mechanical =
INR 2,5-3,5 |
No therapy |
Warfarin has a
relatively narrow terapeutic index. Because it is entirely metabolized in the
liver patients with impaired hepatic function might be expected to increase
sensitivity to the drug. The most serious risks associated with warfarin are
hemorrhage in any tissue or organ, and less frequently, necrosis or gangrene of
the skin and other tissues. Many drugs may affect the response to warfarin:
q
Increased response: acetaminophen, alcohol (acute), allopurinol,
amiodarone, anabolic steroids, antiplatelets, cimetidine, clofibrate,
co-trimoxazole, disulfiram, erytromicin, etacrynic acid, fluoroquinolones,
glucagon, influenza virus vaccine, isoniazid, lovastatin, methylthiouracil,
metronidazole, nalidixic acid, neomycin, NSAIDs, other anticoagulants,
pentoxifylline, propafenone, propoxyphene, propylthouracil, quinidine,
sulfonamides, tamoxifen, tetracycline, thyroid drugs, thrombolytics, tryciclic
antidepressants, thiazides, vitamin E
q
Decreased response: alcohol (chronic use), aminoglutethimide,
barbiturates, carbamazepine, cholestiramine, corticosteroids, corticotropin,
estrogen-conteining products, glutethimide, marcatptopurine, methaqualone,
nafcillin, rifampin, spironolactone, sucralfate, trazodone, vitamin K
Food:
all food containing more than 100 mg vitamin K/100 g may decrease the
anticoagulation response to warfarin, they include: broccoli, Brussels sprouts,
green or white cabbage, cauliflower, kale, lettuce, soybeans, spinach, turnip
greens, beef liver or kidney, and pork liver.
Contraindication: pregnancy, recent surgery or trauma involving brain,
eye, or spinal cord, active major bleeding, blood dyscrasias, arterial aneurysm,
severe hypertension, endocarditis, pericarditis, pericardial effusions, known
hypersensitivity
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