Warfarin sodium
Brand Name: 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 II-prothrombin, VII, IX, and X), resulting in their eventual depletion and prolongation of clotting times.
Indications
· 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
· 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).
Adverse effects
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, Alopecia, urticaria, dermatitis, Nausea, vomiting, anorexia, abdominal cramping, diarrhea, retroperitoneal hematoma, hepatitis, jaundice, mouth ulcers, Priapism, nephropathy, red-orange urine, Granulocytosis, leukopenia, eosinophilia, Fever, "purple toes" syndrome
Drug Interactions:
· Increased bleeding tendencies with salicylates, chloral hydrate, phenylbutazone, clofibrate, disulfiram, chloramphenicol, metronidazole, cimetidine, ranitidine, co-trimoxazole, 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
Nursing considerations
· 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 problems exist.
· 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–drug interaction; dosage of both drugs may need to be adjusted.
· Use caution when discontinuing other medications; warfarin dosage may need to be adjusted; carefully monitor PT values.
· Maintain vitamin K on standby 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.
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