Warfarin NOTES

8/8/2019 Warfarin NOTES

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Warfarin

What Is Warfarin?

Warfarin is an anticoagulant. Anti means against, and coagulant ref ers to blood clotting. Warfarin

reduces the bodys ability to make blood clots. It can help stop harmful clots from forming and

keeps clots from getting larger. Warfarin does not break up existing blood clots.

The most common reasons for taking warfarin include:

y Deep V ein Thrombosis ( DVT):this is a blood clot that occurs in a deep vein. They most often occur in

the legs, but can occur in other parts of your body as well.

y Pulmonary Embolus ( PE):this is a blood clot in the lung. Most often, the blood clot starts in the leg,

breaks off, and travels to the lung.

y Atrial Fibrillation or atrial flutt er:these are irregular heart rhythms that occur in the upper

chambers of the heart (the atria). The atria do not empty all of the blood, which can cause the

leftover blood to form clots which may lead to a stroke.

y Mechanical heart valv e r eplacement:blood clots can form on the mechanical heart valve.

y Heart attack: sometimes warfarin is taken after a heart attack to lower the risk of death, lower the

risk of another heart attack, and lower the risk of stroke.

y Strok e: if a stroke is caused by a blood clot going to the brain, warfarin is used to prevent it from

recurring.

y Transi ent Ischemic Attack (TIA ) or mini strok e : Warfarin is given to prevent a stroke from

occurring.

y Aft er certain surgical proced ur es:some surgical procedures place a person at high risk for

developing a blood clot.

How Does Warfarin Work?

Warfarin inhibits the synthesis of biologically active forms of the vitamin K-dependent clotting factors:

II, VII, IX and X, as well as the regulatory factors protein C, protein S and protein Z. Warfarin inhibits

epoxide reductase thereby diminishing available vitamin K stores and inhibiting production of

functioning coagulation factors.



How and when should a dose be taken?

Take the exact dose once a day at about the same time at least an hour before or after a meal. It is

recommended you take your dose after 4:00 p.m.If you miss a dose and you remember within a f ew

hours, take your usual dose at once. If you dont remember until the next day, DO NOT

take two doses that day to the make up for the missed dose. Doubling the dose could be dangerous.

You shouldnt mix diff erent brands together and you should tell your doctor about other medication

you take including OTC and vitamins.

Warfarin side effects

Stop using warfarin and call your doctor at once if you have a serious side eff ect such as:

y Discoloration anywhere on your body, easy

bruising, purple or red pinpoint spots under

your skin;

y Sudden and severe leg or foot pain, foot

ulcer, purple toes or fingers.

y Headache, dizziness, or weakness;

y unusual bleeding (nose, mouth, vagina, or

rectum), bleeding from wounds or needle

injections.

y blood in your urine, black or bloody stools,

coughing up blood or vomit that looks like

coff ee grounds;

y pale skin, f eeling light-headed or short of

breath, rapid heart rate, trouble

concentrating.

y dark urine, jaundice (yellowing of the

skin or eyes).

y pain in your stomach, back, or sides;

y urinating less than usual or not at all;

y numbness or muscle weakness; or

y any illness with diarrhea, f ever, chills,

body aches, or flu symptoms.

Less serious warfarin side effects may

include:

y nausea, vomiting, mild stomach pain;

y bloating, gas; or

y altered sense of taste.



Drug- food- disease Interactions:

Warfarin interacts with over 600 drugs, food components and medical conditions. These interactions

may increase or decrease warfarins anticoagulant aff ect.

a- The most common medications checked in warfarin prescriptions areas follow:

1- Warfarin Aspirin:

Aspirin, even in small doses, may increase the risk of bleeding in patients on oral anticoagulants by

inhibiting platelet aggregation, prolonging bleeding time, and inducing gastrointestinal lesions.

Patients should be counseled to report any signs of bleeding to their physician, including pain,

swelling, headache, dizziness, weakness, prolonged bleeding from cuts, nosebleeds, bleeding of gums

from brushing, unusual bruising, red or brown urine, or red or black stools and also to avoid any over

the counter oral or topical salicylate products.

2- Warfarin Levothyroxine

Thyroid hormones increase the catabolism of the clotting factors dependent on vitamin K.

INR or prothrombin time should be monitored closely when adding, discontinuing, or changing

thyroid hormone dosage. Patients should be advised to notify their physician if they experience any

signs of excessive anticoagulation, such as unusual or prolonged bleeding, bruising, vomiting, change

in stool or urine color, headache, dizziness, or weakness.

3- Warfarin Rosuvastatin

Rosuvastatinmay enhance the anticoagulant eff ect of warfarin. The INR should be checked

frequently and warfarin dosage adjusted accordingly, especially following initiation, discontinuation

or change of dosage of rosuvastatin in patients who are stabilized on their anticoagulant regimen.

Patients should be advised to promptly report any signs of bleeding to their physician.

4- Warfarin Furosemide

Some loop diuretics may displace warfarin or other oral anticoagulants from plasma protein binding

sites. Plasma warfarin concentrations and warfarin eff ectsmay be increased. Close monitoring of the

INR is recommended, particularly if diuretic dosage must be high. Patients should be advised to

promptly report any signs of bleeding to their physician.



5- Warfarin Escitalopram:

Serotonin reuptake inhibitors (SRIs) may potentiate the risk of bleeding in patients treated with

anticoagulants. Serotonin release by platelets plays an important role in hemostasis, thus SRIs may

alter platelet function and induce bleeding. Additional epidemiological studies have confirmed the

association between use of these agents and the occurrence of upper gastrointestinal bleeding.

Concomitant administration warfarin, specifically, has been associated with an increased frequency

of bleeding without apparent changes in the disposition of either drug or changes in the prothrombin

time.

6- Warfarin Clopidogrel:

Caution and close monitoring of the INR and other bleeding parameters are recommended if

clopidogrel is used in combination with an oral anticoagulant. Patients should be advised to promptly

report any signs of bleeding to their physician.

7- Warfarin Amiodarone

Amiodarone may increase the pharmacologic eff ects of warfarin by inhibiting CYP450 2C9 hepatic

metabolism of S-warfarin resulting in significant anticoagulation. When amiodarone is added to an

anticoagulant regimen there should be a 30-50% reduction in anticoagulant dosage, in addition to

frequentmonitoring of the patient and the prothrombin time or International Normalized Ratio

(INR). Patients should be advised to notify their physician promptly if they experience any signs of

excessive anticoagulation such as unusual or prolonged bleeding.

8- Warfarin Phenobarbital

Barbiturates reduce the eff ects of oral anticoagulants by inducing their hepatic metabolism.

Anticoagulant dosage requirementsmay be increased by 30% to 60%. After the barbiturate is

discontinued, excessive anticoagulation and bleedingmay occur if the anticoagulant dose is not

reduced.

9- Warfarin Rifampicin

Rifampin may decrease the anticoagulant eff ect of warfarin by enhancing CYP450 hepaticmicrosomal

enzyme metabolism of warfarin.Adjustments in warfarin dosage may be needed when rifampin

dosage is added, discontinued, or changed.



10- Warfarin Esomeprazole

Patients should be closely monitored during concomitant therapy with PPIs. The INR should be

checked frequently and warfarin dosage adjusted accordingly, particularly following initiation,

discontinuation or change of dosage of PPI in patients who are stabilized on their warfarin regimen.

11- Warfarin Valproic acid

Monitoring for excessive anticoagulation is recommended during the first week following the

addition of valproic acid to a stabilized regimen of warfarin or other oral anticoagulants. Patients

should be advised to promptly report any signs of bleeding to their physician.

b. Disease interactions:

1- Bleeding disorders:

In general, the use of oral anticoagulants is contraindicated in patients with active bleeding or other

significant risks for bleeding, including hemophilia thrombocytopenia, severe hepatic impairment,

active ulceration of the gastrointestinal or respiratory tracts, cerebrovascular hemorrhage,

aneurysms, pericardial effusions, bacterial endocarditis, eclampsia, preeclampsia, or threatened

abortion. These patientsmay be at increased risk for uncontrollable hemorrhage or bleeding

complications during therapy with oral anticoagulants. The decision to administer anticoagulants

must be based upon clinical judgment in which the risks are weighed against the benefits in each

patient.

2- Diabetes:

Therapy with oral anticoagulants should be administered cautiously in patients with severe

diabetes because they may be at increased risk for hemorrhage. The INR should be monitored

closely, and patients should be advised to promptly report any signs of bleeding to their

physician.

3- Hypertension

In general, the use of oral anticoagulants is contraindicated in patients with malignant or severe,

uncontrolled hypertension. These patients may be at increased risk for cerebral hemorrhage.



Therapy with oral anticoagulants should be administered cautiously in patients with moderate

hypertension.

4- Liver Disease

Oral anticoagulants are primarily metabolized by the liver. Patients with hepatic impairment

may have a heightened response to these agents due to decreased clearance of the drugs as

well as def ective hemostasis associated with impaired synthesis of clotting factors by the liver.

Therapy with oral anticoagulants should be administered cautiously in patients with severe or

moderate liver disease. The INR should be monitored closely, and patients should be advised to

promptly report any signs of bleeding to their physician.

5- Protein C Deficiency:

Tissue necrosis is a rare complication that develops during the initiation of oral anticoagulant

therapy due to thrombotic occlusion of venules in the dermis and subcutaneous tissues.

Hereditary, familial, or clinical deficiencies of protein C or its cofactor, protein S, may be

associated with a hypercoagulable state and an increased risk of the complication. Therapy with

oral anticoagulants should be administered cautiously in patients with known or suspected

deficiency in protein C-mediated anticoagulant response. Concomitant administration with

heparin for the first 5 to 7 days of oral anticoagulant therapy may minimize the risk. If tissue

necrosis develops, oral anticoagulant therapy should be discontinued promptly and vitamin K or

frozen plasma administered at once. Heparin should then be considered for anticoagulation.

6- Decreased response:

Patients with edema, hereditary warfarin resistance, hyperlipidemia, hypothyroidism, or

nephrotic syndrome may exhibit lower than expected hypoprothrombinemic response to oral

anticoagulants. Thus, more frequent laboratory (PT/INR) monitoring and dosage adjustment of

anticoagulantmay be required based on changes in the patient's condition.



7- Increased Response:

Patients with a collagen vascular disease (e.g., systemic lupus erythematosus, rheumatoid

arthritis, scleroderma), congestive heart failure (especially decompensated disease), severe or

prolonged diarrhea, f ever, hyperthyroidism, malabsorption, or steatorrhea may exhibit greater

than expected hypoprothrombinemic response to oral anticoagulants. Thus, more frequent

laboratory (PT/INR) monitoring and dosage adjustment of anticoagulant may be required based

on changes in the patient's condition. Patients should be advised to promptly report any signs of

bleeding to their physician.

c. Diet interactions:

When taking warfarin the diet should not be dramatically changed because this may aff ect the results

of INR tests.

Foods with high amounts of vitamin K and that may antagonize warfarin:

y Tea

y Liver

y Broccoli

y Cabbage

y Lettuce

y Mustard greens

y Parsley

y Spinach

y Mayonnaise

Herbal products that may increase the risk for bleeding:

y Aloe

y Aniseed

y Clove

y Onion

y Fenugreek

y Garlic

y Red Clover

y Ginger

y Ginkgo

y Wild Carrot

y Horse Chestnut

y Celery

y Chamomile

y Licorice

y Ginseng

Warfarin NOTES

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