Warfarin Sodium

warfarin sodium (war' far in) Coumadin, Warfilone (CAN) Pregnancy Category X Drug classes

Oral anticoagulant Coumarin derivative Therapeutic actions

Interferes with the hepatic synthesis of vitamin K-dependent clotting factors (factors IIprothrombin, VII, IX, and X), resulting in their eventual depletion and prolongation of clotting times. Indications

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Venous thrombosis and its extension, treatment, and prophylaxis Treatment of thromboembolic complications of atrial fibrillation with embolization, and cardiac valve replacement Pulmonary embolism, treatment, and prophylaxis Prophylaxis of systemic embolization after acute MI Unlabeld uses: prevention of recurrent TIAs, prevention of recurrent MI, adjunct to therapy in small-cell carcinoma of the lung

Contraindications and cautions

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Contraindicated with allergy to warfarin; SBE; hemorrhagic disorders; TB; hepatic diseases; GI ulcers; renal disease; indwelling catheters, spinal puncture; aneurysm; diabetes; visceral carcinoma; uncontrolled hypertension; severe trauma (including recent or contemplated CNS, eye surgery; recent placement of IUD); threatened abortion, menometrorrhagia; pregnancy (fetal damage and death); lactation (suggest using heparin if anticoagulation is required). Use cautiously with CHF, diarrhea, fever; thyrotoxicosis; senile, psychotic, or depressed patients.

Available forms

Tablets—1, 2, 2.5, 3, 4, 5, 6, 7.5, 10 mg; powder for injection—2 mg Dosages

Adjust dosage according to the one-stage PT to achieve and maintain 1.5–2.5 times the control value or prothrombin activity 20%–30% of normal; PT ratio of 1.3–1.5 or INR of 2–3. IV use is reserved for situations in which oral warfarin is not feasible. Dosages are the same for oral and IV forms. ADULTS

Initially, 2–5 mg/day PO. Adjust dose according to PT response. For maintenance, 2– 10 mg/day PO based on PT ratio or INR. GERIATRIC PATIENTS

Lower doses are usually needed; begin dosage lower than adult recommended and closely monitor PT ratio or INR. Pharmacokinetics Route Oral

Peak 1.5–3 days

Duration 2–5 days

Metabolism: Hepatic; T1/2: 1–2.5 days Distribution: Crosses placenta; enters breast milk Excretion: Feces and urine IV facts

Preparation: Reconstitute vial with 2.7 mL of sterile water. Protect from light. Use within 4 hr of reconstitution. Infusion: Inject slowly over 1–2 min; switch to oral preparation as soon as possible. Adverse effects

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Dermatologic: Alopecia, urticaria, dermatitis GI: Nausea, vomiting, anorexia, abdominal cramping, diarrhea, retroperitoneal hematoma, hepatitis, jaundice, mouth ulcers GU: Priapism, nephropathy, red-orange urine Hematologic: Granulocytosis, leukopenia, eosinophilia; hemorrhage; GI or urinary tract bleeding (hematuria, dark stools; paralytic ileus, intestinal obstruction from hemorrhage into GI tract); petechiae and purpura, bleeding from mucous membranes; hemorrhagic infarction, vasculitis, skin necrosis of female breast; adrenal hemorrhage and resultant adrenal insufficiency; compressive neuropathy secondary to hemorrhage near a nerve Other: Fever, "purple toes" syndrome

Interactions

Drug-drug • Increased bleeding tendencies with salicylates, chloral hydrate, phenylbutazone, clofibrate, disulfiram, chloramphenicol, metronidazole, cimetidine, ranitidine, cotrimoxazole, sulfinpyrazone, quinidine, quinine, oxyphenbutazone, thyroid drugs, glucagon, danazol, erythromycin, androgens, amiodarone, cefamandole, cefoperazone, cefotetan, moxalactam, cefazolin, cefoxitin, ceftriaxone, meclofenamate, mefenamic acid, famotidine, nizatidine, nalidixic acid • Decreased anticoagulation effect may occur with barbiturates, griseofulvin, rifampin, phenytoin, glutethimide, carbamazepine, vitamin K, vitamin E, cholestyramine, aminoglutethimide, ethchlorvynol • Altered effects with methimazole, propylthiouracil • Increased activity and toxicity of phenytoin when taken with oral anticoagulants Drug-lab test • Red-orange discoloration of alkaline urine may interfere with some lab tests

Drug-alternative therapy • Increased risk of bleeding if combined with angelica, cat's claw, chamomile, chondroitin, feverfew, garlic, ginkgo, goldenseal, grape seed extract, green leaf tea, horse chestnut seed, psyllium, and tumeric therapy Nursing considerations Assessment

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History: Allergy to warfarin; SBE; hemorrhagic disorders; TB; hepatic diseases; GI ulcers; renal disease; indwelling catheters, spinal puncture; aneurysm; diabetes; visceral carcinoma; uncontrolled hypertension; severe trauma; threatened abortion, menometrorrhagia; pregnancy; lactation; CHF, diarrhea, fever; thyrotoxicosis; senile, psychotic or depressed patients Physical: Skin lesions, color, temperature; orientation, reflexes, affect; P, BP, peripheral perfusion, baseline ECG; R, adventitious sounds; liver evaluation, bowel sounds, normal output; CBC, urinalysis, guaiac stools, PT, renal and hepatic function tests

Interventions

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Do not use drug if patient is pregnant (heparin is anticoagulant of choice); advise patient to use contraceptives. Monitor PT ratio or INR regularly to adjust dosage. Administer IV form to patients stabilized on Coumadin who are not able to take oral drug. Dosages are the same. Return to oral form as soon as feasible. Do not change brand names once stabilized; bioavailability may be a problem. Evaluate patient regularly for signs of blood loss (petechiae, bleeding gums, bruises, dark stools, dark urine). Maintain PT ratio of 1.3–1.5, 1.5–2 with mechanical prosthetic valves or recurrent systemic embolism; INR ratio of 2–3, 3–4.5 with mechanical prosthetic valves or recurrent systemic emboli. Do not give patient any IM injections. Double check all drugs ordered for potential drug interaction; dosage of both drugs may need to be adjusted. Use caution when discontinuing other drugs; warfarin dosage may need to be adjusted; carefully monitor PT values. Keep vitamin K readily available in case of overdose. Arrange for frequent follow-up, including blood tests to evaluate drug effects. Evaluate for therapeutic effects: PT 1.5–2.5 times the control value; PT ratio, INR within therapeutic range.

Teaching points

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Many factors may change your body's response to this drug—fever, change of diet, change of environment, other medications. Your dosage may have to be changed repeatedly. Write down changes that are prescribed. Do not start or stop taking any medication without consulting your health care provider. Other drugs can affect your anticoagulant; starting or stopping another drug can cause excessive bleeding or interfere with the desired drug effects.

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Carry or wear a medical ID tag to alert emergency medical personnel that you are taking this drug. Avoid situations in which you could be easily injured (contact sports, shaving with a straight razor). Have periodic blood tests to check on the drug action. These tests are important. Use contraception; do not become pregnant while taking this drug. These side effects may occur: Stomach bloating, cramps (transient); loss of hair, rash; orange-red discoloration to the urine (if upsetting, add vinegar to your urine and the color should disappear). Report unusual bleeding (from brushing your teeth, excessive bleeding from injuries, excessive bruising), black or bloody stools, cloudy or dark urine, sore throat, fever, chills, severe headaches, dizziness, suspected pregnancy.

Adverse effects in Italic are most common; those in Bold are life-threatening.