Hematologic: Oral Anticoagulants Flashcards
What is the generic and brand name of oral anticoagulants?
Warfarin [Coumadin]
How fast is warfarin absorbed?
Rapid
How long does it take to see effects of warfarin?
36 to 48 hours
When do full effects of warfarin occur?
3 to 4 days
Why does it take so long to to see effects of warfarin?
- Warfarin antagonizes the production of vitamin K–
dependent clotting factors. - Before warfarin can exhibit its full effect,
the circulating vitamin K clotting factors must be exhausted.
What does warfarin bind to?
Plasma albumin
Where is warfarin metabolized?
Liver
Where is warfarin excreted?
Urine
Because warfarin is highly protein
bound and metabolized in the liver what can occur?
- Using other drugs at the same time
may alter the amount of warfarin in the body. - This may increase the risk of bleeding and clotting
Detailed Pharmacodynamics of warfarin
Oral anticoagulants alter the ability of the liver to synthesize vitamin K–dependent clotting factors, including factors II (prothrombin), VII, IX, and X. However, clotting factors already in the bloodstream
continue to coagulate blood until they become depleted, so anticoagulation doesn’t begin immediately.
What is warfarin used to treat?
- Thromboembolism
- Can be started while a patient is still receiving heparin
- Prevention of PE caused by DVT, MI, rheumatic
fever, prosthetic heart valves, or chronic atrial fibrillation - Combined with an antiplatelet drugs to decrease the risk of arterial clotting.
Action of warfarin
Inhibits vitamin K–dependent activation of clotting factors II(prothrombin), VII, IX, and X formed in the liver
Adverse reactions of warfarin
- hemorrhage
- prolonged clotting time
- rash
- fever
- diarrhea
- hepatitis
What to monitor for in patient receiving warfarin
- Bleeding gums
- bruises
- petechiae
- epistaxis
- tarry stools
- hematuria
- hematemesis
What can cause warfarin to become ineffective?
vitamin K
What labs to monitor in patients receiving warfarin
- HGB and HCT
- Platelet count
- PT
- INR
- PTT
what drugs are warfarin combined with decrease the risk of arterial clotting?
Antiplatelet drugs such as:
- Aspirin
- Clopidogrel
- Dipyridamole
REACTION when taken with Warfarin:
acetaminophen, allopurinol, amiodarone,
cephalosporins, cimetidine, ciprofloxacin, clofibrate, danazol, diazoxide, disulfiram, erythromycin, fluoroquinolones, glucagon, heparin, ibuprofen, isoniazid, ketoprofen, metronidazole, miconazole, neomycin, propafenone, propylthiouracil, quinidine,
streptokinase, sulfonamides, tamoxifen, tetracyclines, thiazides, thyroid drugs, tricyclic antidepressants, urokinase, and vitamin E
- These are highly protein-bound medications
- Increase the effects of warfarin
- Resulting in an increased risk of bleeding.
REACTION when taken with Warfarin:
barbiturates, carbamazepine, corticosteroids, corticotropin, mercaptopurine, nafcillin, hormonal contraceptives containing estrogen, rifampin,
spironolactone, sucralfate, and trazodone
Drugs metabolized by the liver may increase or decrease the
effectiveness
REACTION when taken with Warfarin:
diet high in vitamin K
reduces the effectiveness
REACTION when taken with Warfarin:
phenytoin
- Risk of phenytoin toxicity increases
2. Increase or decrease the effects of
REACTION when taken with Warfarin:
Vitamin K and fresh frozen plasma
reduce the effects of warfarin
What else can effect the response of warfain?
alcohol abuse increases the risk of clotting
The primary adverse reaction to oral anticoagulant
minor
bleeding
