Warfarin
Anticoagulant/Antiplatelet · Anticoagulant
Indications
Thromboembolic conditions. Prophylaxis of embolisation in rheumatic heart disease and atrial fibrillation. Prophylaxis after insertion of prosthetic heart valve. Prophylaxis and treatment of venous thrombosis and pulmonary embolism. Transient ischaemic attacks.
Dosage
Adults: 10-15 mg daily, adjust dosage according to test results. Patients who do not require rapid anticoagulation and elderly patients should be given a lower induction dose. Maintenance, 3-9 mg daily, to be taken at the same time each day. Children: Not recommended.
Adverse Effects
Alopecia, rash, diarrhoea, fall in haematocrit, haemorrhage, skin reaction, GI upset, decreased hemoglobin, fever, pancreatitis, jaundice, hepatic dysfunction. Reports of calciphylaxis.
Risk Factor (Pregnancy/Lactation)
Pregnancy: Contraindicated in pregnancy. Lactation: Caution advised or effect undetermined. Contraindications: Haemorrhagic conditions. Impaired renal or hepatic function. Within 24 hours of surgery or labour. Precautions: Hypertension. Weight changes, elderly, renal impairment, acute illness, vit K deficiency, GI upset, risk factors for haemorrhage, protein C or S deficiency, thyroid disorders, smoking cessation, polymorphisms in CYP2C9 or VKORC1.
Interactions
NSAIDs, oral hypoglycaemics, sulphonamides, quinidine, antibiotics, phenformin, cimetidine, drugs affecting liver enzymes, corticosteroids, imidazole antifungals, tamoxifen, antiplatelets, antithrombotics, other anticoagulants, antidepressants, disulfiram, fibrates, statins, antiarrhythmics, propafenone, sulfonamides, sex hormones, oral contraceptives, allopurinol, cytotoxics, PPIs, paracetamol, danazol, thyroid hormones, methylphenidate, zafirlukast, barbiturates, anticonvulsants, rifampicin, azathioprine, nevirapine, ritonavir, sucralfate, alcohol, colestyramine, glucosamine, St John's wort, cranberry juice, vit K.
Advice to Patient
Take with or without meals as advised by prescriber. Contact prescriber if there is unusual bleeding or bruising, dark stool, skin rash or irritation, unusual fever, persistent nausea or GI discomfort, joint pain, back pain, swelling or pain at injection site. Avoid alcohol during therapy. To prevent bleeding, use soft toothbrush, floss with waxed floss, use electric razor, avoid scissors or sharp knives and harmful activities. Eat consistent amount of vitamin K-rich foods such as green tea, beef liver, dark green leafy vegetables. Keep weekly follow-up appointments for blood tests after discharge until PT and INR levels become normal. Patients with diabetes must wear or carry identification card indicating diabetes.
Pharmacokinetics
Onset of action: Anticoagulation: Oral: 24-72 hrs. Peak effect: Full therapeutic effect: 5-7 days. Duration: 2-5 days. Absorption: Oral: Rapid, complete. Metabolism: Hepatic. Half-life elimination: 20-60 hrs. Time to peak, plasma: Oral: Approx. 4 hrs. Excretion: Urine.
Unlicensed Use
Children: Treatment and prophylaxis of thrombotic episodes: Oral. Neonate 200 mcg/kg as a single dose on first day, reduced to 100 mcg/kg once daily for following 3 days (but if INR still below 1.4 use 200 mcg/kg once daily, or if INR above 3 use 50 mcg/kg once daily, if INR above 3.5 omit dose); then adjusted according to INR, usual maintenance 100-300 mcg/kg once daily (may need up to 400 mcg/kg once daily especially if bottle fed); 1 mth-18 yr, 200 mcg/kg (max 10 mg) as a single dose on first day, reduced to 100 mcg/kg (max 5 mg) once daily for following 3 days (but if INR still below 1.4 use 200 mcg/kg (max 10 mg) once daily, or if INR above 3 use 50 mcg/kg (max 2.5 mg) once daily, or if INR above 3.5 omit dose); then adjusted according to INR, usual maintenance 100-300 mcg/kg once daily (may need up to 400 mcg/kg once daily especially if bottle fed). Induction dose may need to be…
Brands with this active ingredient
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