Generic Name

warfarin sodium

Brand Names

  • Apo-Warfarin (CAN)
  • Coumadin
  • Gen-Warfarin (CAN)

Drug classification

  • Oral anticoagulant
  • Coumarin derivative
  • Pregnancy Category X

Dosage & Route

  • Available forms :Tablets—1, 2, 2.5, 3, 4, 5, 6, 7.5, 10 mg; powder for injection—5.4 mg reconstitutes to 2 mg/mL
  • 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 with smaller doses than those recommended for adults and closely monitor PT ratio or INR.

Therapeutic actions

  • Warfarin inhibits synthesis of vit K-dependent coagulation factors VII, IX, X and II and anticoagulant protein C and its cofactor protein S. No effects on established thrombus but further extension of the clot can be prevented. Secondary embolic phenomena are avoided.

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
  • Unlabeled uses: Prevention of recurrent TIAs, prevention of recurrent MI, adjunct to therapy in small-cell carcinoma of the lung

Adverse effects

  • Hypersensitivity, rash, alopecia, diarrhea, drop in hematocrit, purple toes syndrome, skin necrosis, jaundice, nausea, vomiting, hepatic dysfunction, pancreatitis, increased LFT.

[box type="note"]Potentially Fatal: Hemorrhage.[/box]

Contraindications

  • Hypersensitivity; hemorrhagic tendencies or blood dyscrasia; recent surgery; peptic ulcer; severe hypertension; bacterial endocarditis; cerebrovascular disorders; psychosis; senility; aneurysms; pericarditis; pericardial effusion; eclampsia; pre-eclampsia; threatened abortion; alcoholism; severe renal and hepatic impairment; pregnancy.

Nursing considerations

Assessment

  • 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, T; orientation, reflexes, affect; P, BP, peripheral perfusion, baseline ECG; R, adventitious sounds; liver evaluation, bowel sounds, normal output; CBC, urinalysis, guaiac stools, PT, LFTs, renal function tests

Interventions

  • 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.

[box type="note"]WARNING: 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.[/box]

  • Do not give patient any IM injections.

[box type="note"] WARNING: Double check all drugs ordered for potential drug interactions; dosage of both drugs may need to be adjusted.[/box]

  • 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.

[box type="note"] WARNING: Evaluate for therapeutic effects: INR within therapeutic range.[/box]

Teaching points

  • 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.
  • 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.
  • You may experience these side effects: 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.

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