Warfarin

Warfarin

Mechanism of Action:

• Interferes with hepatic synthesis of vitamin K–dependent clotting factors, resulting in depletion of coagulation factors II, VII, IX, X
• Thus, the predominant action of warfarin is on the extrinsic pathway of the clotting cascade.

Indications: 

• DVT                                                
• Prophylaxis of VTE in AF, rheumatic heart disease and in patients with prosthetic heart valves.
• PE
• Prophylaxis, treatment of thromboembolic disorders and embolic complications arising from atrial fibrillation or valve replacement.
• Risk reduction of systemic embolism following MI (e.g., recurrent MI, stroke).
• OFF-LABEL: Adjunct treatment in transient ischemic attacks.

Cautions and Contraindications:

• Peptic Ulceration
• Severe hypertension
• Pregnancy (due to teratogenicity)
• Caution if recent surgery.

Side – Effects:

• Hemorrhage
• Skin Necrosis (due to thrombosis in the microvasculature of subcutaneous fat.)
• Hepatic Dysfunction

Metabolism and Half- Life:

• T ½ Is 20-60 hrs.; Well – absorbed from GI tract.  
• Metabolized by the liver.
• Primarily excreted in urine.

Monitoring:

Monitor INR (initially daily and then at progressively lengthening intervals when steady INR is achieved)

Drug Interactions:

The anticoagulant effect of Warfarin is increased by: –

• Antibiotics ( due to reduced vitamin K synthesis by gut flora)
• Amiodarone and diuretics ( displace warfarin from plasma proteins)
• Cimetidine, fluconazole, alcohol( reduce the metabolism of warfarin)
• Aspirin, Clopidogrel, NSAIDs ( due to impaired platelet function)
• Also, by advanced age, biliary disease, CCF, hyperthyroidism , cranberry juice and intermittent alcohol binges.

The anticoagulant effect of Warfarin is reduced by: –

• Antiepileptic agents, rifampicin, alcoholism( due to induction of hepatic enzymes)
• Estrogens and OCP (increase the concentration of vitamin – K – dependent clotting factors)
• Also, by hypothyroidism and nephrotic syndrome.

NURSING CONSIDERATIONS

Baseline assessment

• Cross-check dose with co-worker.
• Obtain CBC, PT/INR before administration and daily following therapy initiation.
• When stabilized, follow with INR determination q4–6wks.
• Obtain genotyping prior to initiating therapy if available.
• Screen for major active bleeding. Question recent history of bleeding, recent trauma, surgical procedures, epidural anesthesia.

Intervention/evaluation

• Monitor INR diligently. Assess CBC for anaemia; urine/stool for occult blood.
• Be alert to complaints of abdominal/ back pain, severe headache, confusion, seizures, hemiparesis, aphasia (may be sign of haemorrhage). Decrease in B/ P, increase in pulse rate may be sign of haemorrhage.
• Question for increase in amount of menstrual discharge.
• Assess peripheral pulses; skin for ecchymoses, petechiae.
• Check for excessive bleeding from minor cuts, scratches. Assess gums for erythema, gingival bleeding

Patient/family teaching

• Take medication at same time each day.
• •Blood levels will be monitored routinely.
• Do not take, discontinue any other medication except on advice of physician.
• Avoid alcohol, aspirin, drastic dietary changes.
• Consult with physician before surgery, dental work.
• Urine may become red orange.
• Falls, subtle injuries, esp. head or abdominal trauma, can be life-threatening.
• Report bleeding, bruising, red or brown urine, black stools.
• Use electric razor, soft toothbrush to prevent bleeding.
• Report coffee-ground vomitus, blood-tinged mucus from cough.
• Do not use any medication without physician approval (may interfere with platelet aggregation).
• •Seek immediate medical attention for stroke-like symptoms (confusion, difficulty speaking, headache, one-sided weakness); bloody stool or urine

Important points:

• Foods rich in vitamin K(e.g., spinach, brussels sprouts, meat)may decrease effect. Cranberry juice may increase effect.
• Effects proteins C and S precede anticoagulant effect thereby transiently increasing the risk of thrombosis;
• Anticoagulation with heparin should, therefore, be used concomitantly for at least 5 days and untill INR is within the target range for treatment of a thrombotic event.
• Target INR depends on indication ( e.g., 2.0 – 3.0 for VTE and AF ; 3.0- 4.5 for prosthetic heart valves; 4.0- 5.0 for high – risk heart valves).
• Vitamin – K may be used to reverse anticoagulation with warfarin; use should be limited to major bleeding or high INR in a patient with other risk factors for bleeding.
• Prothrombin complex concentrate may so be used to reverse effects of Warfarin in severe bleeding.

REFERENCES

1. Robert Kizior, Keith Hodgson, Saunders Nursing Drug handbook,1st edition 2024, Elsevier Publications. ISBN-9780443116070
2. McGraw Hill- Drug Handbook, Seventh Edition, 2013, McGraw Hill Education Publications,9780071799430.
3. April Hazard, Cynthia Sanoski, Davi’s Drug Guide for Nurses -Sixteenth Edition 2019, FA Davis Company Publications,9780803669451.
4. Jones and Bartlet, Pharmacology for Nurses, Second Edition, 2020, Jones and Bartlet Learning Publications, ISBN 9781284141986.
5. Nursebro.com, Search – Nursebro

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