warfarin sodium A

war-far-in

(Apo-Warfarin  J, Coumadin, Gen-Warfarin  J, Jantoven, Tar-Warfarin  J)

Do not confuse Coumadin with Kemadrin.

 CLASSIFICATION

PHARMACOTHERAPEUTIC: Coumarin derivative. CLINICAL: Anticoagulant.

ACTION

A coumarin derivative that interferes with hepatic synthesis of vitamin KUdependent clotting factors, resulting in depletion of coagulation factors II, VII, IX, and X. Therapeutic Effect: Prevents further extension of formed existing clot; prevents new clot formation or secondary thromboembolic complications.

PHARMACOKINETICS

            Route Onset            Peak             Duration       

            PO      1.5U3 days    5U7 days       N/A   

Well absorbed from the GI tract. Metabolized in the liver. Primarily excreted in urine. Not removed by hemodialysis. Half-life: 1.5U2.5 days.

USES

Anticoagulant, including the following: Prophylaxis, treatment of venous thrombosis, pulmonary embolism. Treatment of thromboembolism associated with chronic atrial fibrillation. Adjunct in treatment of coronary occlusion. Prophylaxis and treatment of thromboembolic complications associated with cardiac valve replacement. Reduces risk of death, recurrent MI, stroke, embolization after MI. OFF-LABEL: Prevention of myocardial infarction, recurrent cerebral embolism; treatment adjunct in transient ischemic attacks.

PRECAUTIONS

CONTRAINDICATIONS: Neurosurgical procedures, open wounds, pregnancy, severe hypertension, severe hepatic or renal damage, spinal puncture, uncontrolled bleeding, ulcers. CAUTIONS: Active tuberculosis, diabetes, heparin-induced thrombocytopenia, those at risk for hemorrhage, necrosis, gangrene.

B LIFESPAN CONSIDERATIONS: Pregnancy/Lactation: Contraindicated in pregnancy (fetal or neonatal hemorrhage, intrauterine death). Crosses placenta; is distributed in breast milk. Pregnancy Category D. Children: More susceptible to effects. Elderly: Increased risk of hemorrhage; lower dosage recommended.

INTERACTIONS

DRUG: Acetaminophen, allopurinol, amiodarone, anabolic steroids, androgens, aspirin, cefamandole, cefoperazone, chloral hydrate, chloramphenicol, cimetidine, clofibrate, danazol, dextrothyroxine, diflunisal, disulfiram, erythromycin, fenoprofen, gemfibrozil, indomethacin, methimazole, metronidazole, oral hypoglycemics, phenytoin, plicamycin, propylthiouracil, quinidine, salicylates, sulfinpyrazone, sulfonamides, sulindac: Warfarin increases the effects of these drugs. Alcohol: May enhance warfarin's anticoagulant effect. Barbiturates, carbamazepine, cholestyramine, colestipol, estramustine, estrogens, griseofulvin, primidone, rifampin, vitamin K: Warfarin decreases the effects of these drugs. HERBAL: American ginseng, St. John's wort: May decrease the effectiveness of warfarin. Feverfew, garlic, ginkgo biloba, ginseng, glucosamine-chondroitin: May increase the risk of bleeding. FOOD: None known. LAB VALUES: None known.

AVAILABILITY (Rx)

TABLETS (COUMADIN, JANTOVEN): 1 mg, 2 mg, 2.5 mg, 3 mg, 4 mg, 5 mg, 6 mg, 7.5 mg, 10 mg.

ADMINISTRATION/HANDLING

PO

N Scored tablets may be crushed. N Give without regard to food. Give with food if GI upset occurs.

INDICATIONS/ROUTES/DOSAGE

ANTICOAGULANT

PO: ADULTS, ELDERLY: Initially, 5U15 mg/day for 2U5 days; then adjust based on INR. Maintenance: 2U10 mg/day. CHILDREN: Initially, 0.1U0.2 mg/kg (maximum 10 mg). Maintenance: 0.05U0.34 mg/kg/day.

USUAL ELDERLY DOSAGE (MAINTENANCE)

PO, IV: ELDERLY: 2U5 mg/day.

SIDE EFFECTS

OCCASIONAL: GI distress, such as nausea, anorexia, abdominal cramps, diarrhea. RARE: Hypersensitivity reaction, including dermatitis and urticaria, especially in those sensitive to aspirin.

ADVERSE REACTIONS/TOXIC EFFECTS

Bleeding complications ranging from local ecchymoses to major hemorrhage may occur. Drug should be discontinued immediately and vitamin K or phytonadione administered. Mild hemorrhage: 2.5U10 mg PO, IM, or IV. Severe hemorrhage: 10U15 mg IV and repeated q4h, as necessary. Hepatotoxicity, blood dyscrasias, necrosis, vasculitis, and local thrombosis occur rarely.

NURSING CONSIDERATIONS

BASELINE ASSESSMENT

Cross-check dose with coworker. Determine INR before administration and daily following therapy initiation. When stabilized, follow with INR determination q4U6wk.

INTERVENTION/EVALUATION

Monitor INR reports diligently. Assess Hct, platelet count, urine and stool culture for occult blood, AST, ALT, regardless of route of administration. Be alert to complaints of abdominal or back pain, severe headache (may be signs of hemorrhage). Decrease in BP, increase in pulse rate may also be sign of hemorrhage. Question for increase in amount of discharge during menses. Assess area of thromboembolus for color, temperature. Assess peripheral pulses; skin for ecchymoses, petechiae. Check for excessive bleeding from minor cuts, scratches. Assess gums for erythema, gingival bleeding. Assess urine output for hematuria.

PATIENT/FAMILY TEACHING

N Take medication exactly as prescribed. N Do not take or discontinue any other medication except on advice of physician. N Avoid alcohol, salicylates, drastic dietary changes. N Do not change from one brand to another. N Consult with physician before surgery or dental work. N Urine may become red-orange. N Notify physician if bleeding, bruising, red or brown urine, black stools occur. N Use electric razor, soft toothbrush to prevent bleeding. N Report coffee-ground vomitus, blood-tinged mucus from cough. N Do not use any OTC medication without physician approval (may interfere with platelet aggregation).