Farin
Generic Name
Warfarin Sodium
Manufacturer
Square Pharmaceuticals Ltd.
Country
Bangladesh
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Price Details
Current market pricing information
| Variant | Unit Price | Strip Price |
|---|---|---|
| farin 2 mg tablet | ৳ 2.00 | ৳ 20.00 |
Description
Overview of the medicine
Warfarin is an anticoagulant used to prevent and treat blood clots (thrombosis). It works by decreasing the clotting ability of the blood.
Uses & Indications
Dosage
Adults
Initial dose typically 2-5 mg orally once daily. Dosage is highly individualized based on the patient's INR response to achieve a target INR, usually between 2.0-3.0 for most indications. Adjustments are made based on daily or frequent INR monitoring.
Elderly
Lower initial doses (e.g., 2 mg/day) are often recommended for elderly patients due to increased sensitivity to warfarin and higher risk of bleeding. Close INR monitoring is essential.
Renal_impairment
No specific dose adjustment is generally required for patients with renal impairment, as warfarin is primarily metabolized by the liver. However, close INR monitoring is advised, especially in severe renal dysfunction, due to potential altered protein binding or bleeding risk.
How to Take
Take orally, usually once daily at the same time each day. It can be taken with or without food. Consistency in timing is more important than relation to meals.
Mechanism of Action
Warfarin inhibits vitamin K epoxide reductase, an enzyme responsible for regenerating reduced vitamin K. Reduced vitamin K is a cofactor for gamma-carboxylation of clotting factors II, VII, IX, X, and anticoagulant proteins C and S. By depleting functional vitamin K, warfarin impairs the synthesis of these clotting factors, thus exerting its anticoagulant effect.
Pharmacokinetics
Onset
Initial anticoagulant effects are observed within 24-72 hours, but the peak anticoagulant effect (reflected by INR) is typically achieved within 5-7 days.
Excretion
Metabolites are excreted in the urine (primarily) and feces. Less than 1% of the unchanged drug is excreted in the urine.
Half life
The half-life of warfarin varies from 20 to 60 hours, with an average of approximately 40 hours.
Absorption
Rapidly and completely absorbed from the gastrointestinal tract. Peak plasma concentrations are typically reached within 2-8 hours.
Metabolism
Primarily metabolized in the liver by cytochrome P450 enzymes, mainly CYP2C9, CYP1A2, CYP2C19, CYP3A4, CYP2C8, and CYP2C18. The main metabolites are inactive.
Side Effects
Contraindications
- Pregnancy (category X - causes fetal hemorrhage and embryopathy).
- Hemorrhagic tendencies or blood dyscrasias.
- Recent or contemplated surgery of the central nervous system or eye.
- Recent major surgery with large open wounds.
- Severe uncontrolled hypertension.
- Bacterial endocarditis.
- Pericarditis and pericardial effusion.
- Lumbar puncture, spinal anesthesia, or other diagnostic or therapeutic procedures with potential for uncontrollable bleeding.
Drug Interactions
Amiodarone
Significantly potentiates warfarin's anticoagulant effect, requiring substantial warfarin dose reduction (e.g., 30-50%) and close INR monitoring.
Aspirin/NSAIDs
Increased risk of bleeding by inhibiting platelet function and/or irritating the GI mucosa.
Phenytoin/Carbamazepine
May alter warfarin metabolism (inducers or inhibitors), leading to variable effects on INR. Close monitoring required.
Herbal supplements (e.g., Ginko Biloba, Garlic, Ginseng)
Many herbal supplements can increase bleeding risk or alter warfarin's effectiveness. Consult physician before use.
Antibiotics (e.g., Ciprofloxacin, Metronidazole, Trimethoprim/sulfamethoxazole)
Can potentiate warfarin's anticoagulant effect by affecting gut flora and vitamin K synthesis, leading to increased INR and bleeding risk.
Storage
Store below 30°C in a dry place, protected from light and moisture. Keep out of reach of children.
Overdose
Symptoms of overdose include excessive bleeding (e.g., hematuria, melena, ecchymoses, epistaxis, gingival bleeding). Management involves discontinuing warfarin, administering Vitamin K (oral or IV), and in severe cases with active bleeding or high INR, administration of fresh frozen plasma (FFP) or prothrombin complex concentrate (PCC) to rapidly reverse anticoagulation.
Pregnancy & Lactation
Warfarin is contraindicated during pregnancy (Pregnancy Category X) due to the risk of fetal hemorrhage and congenital malformations (warfarin embryopathy). It is generally considered compatible with breastfeeding, as very small amounts are transferred into breast milk; however, caution is advised, and the infant should be monitored for signs of bleeding or bruising.
Side Effects
Contraindications
- Pregnancy (category X - causes fetal hemorrhage and embryopathy).
- Hemorrhagic tendencies or blood dyscrasias.
- Recent or contemplated surgery of the central nervous system or eye.
- Recent major surgery with large open wounds.
- Severe uncontrolled hypertension.
- Bacterial endocarditis.
- Pericarditis and pericardial effusion.
- Lumbar puncture, spinal anesthesia, or other diagnostic or therapeutic procedures with potential for uncontrollable bleeding.
Drug Interactions
Amiodarone
Significantly potentiates warfarin's anticoagulant effect, requiring substantial warfarin dose reduction (e.g., 30-50%) and close INR monitoring.
Aspirin/NSAIDs
Increased risk of bleeding by inhibiting platelet function and/or irritating the GI mucosa.
Phenytoin/Carbamazepine
May alter warfarin metabolism (inducers or inhibitors), leading to variable effects on INR. Close monitoring required.
Herbal supplements (e.g., Ginko Biloba, Garlic, Ginseng)
Many herbal supplements can increase bleeding risk or alter warfarin's effectiveness. Consult physician before use.
Antibiotics (e.g., Ciprofloxacin, Metronidazole, Trimethoprim/sulfamethoxazole)
Can potentiate warfarin's anticoagulant effect by affecting gut flora and vitamin K synthesis, leading to increased INR and bleeding risk.
Storage
Store below 30°C in a dry place, protected from light and moisture. Keep out of reach of children.
Overdose
Symptoms of overdose include excessive bleeding (e.g., hematuria, melena, ecchymoses, epistaxis, gingival bleeding). Management involves discontinuing warfarin, administering Vitamin K (oral or IV), and in severe cases with active bleeding or high INR, administration of fresh frozen plasma (FFP) or prothrombin complex concentrate (PCC) to rapidly reverse anticoagulation.
Pregnancy & Lactation
Warfarin is contraindicated during pregnancy (Pregnancy Category X) due to the risk of fetal hemorrhage and congenital malformations (warfarin embryopathy). It is generally considered compatible with breastfeeding, as very small amounts are transferred into breast milk; however, caution is advised, and the infant should be monitored for signs of bleeding or bruising.
Frequently Asked Questions
Common questions about this medicine
Pack Sizes
Shelf Life
2-3 years from the date of manufacture, specific to lot. Refer to packaging for exact expiry date.
Availability
Pharmacies, hospitals
Approval Status
Approved by regulatory authorities
Patent Status
Off-patent
WHO Essential Medicine
YesClinical Trials
Extensive clinical trials have established warfarin's effectiveness and safety in preventing and treating various thromboembolic conditions, including venous thromboembolism, atrial fibrillation, and after myocardial infarction. Ongoing research continues to optimize its use, particularly in genetically susceptible populations.
Lab Monitoring
- International Normalized Ratio (INR) – regularly, as directed by the physician, to guide dosing.
- Complete Blood Count (CBC) – periodically to check for anemia or other blood dyscrasias.
- Liver function tests (LFTs) – periodically, especially in patients with pre-existing liver conditions.
Doctor Notes
- Crucial to emphasize strict adherence to dosing and INR monitoring schedule.
- Educate patients thoroughly on signs and symptoms of bleeding and the importance of dietary consistency.
- Carefully review all concomitant medications and herbal supplements for potential interactions.
- Consider genetic testing (CYP2C9, VKORC1) in select patients to guide initial dosing and minimize risks.
Patient Guidelines
- Take warfarin exactly as prescribed, at the same time each day.
- Do not start or stop any other medication, including over-the-counter drugs, herbal supplements, or new foods, without consulting your doctor or pharmacist.
- Report any signs of unusual bleeding (e.g., prolonged nosebleeds, bleeding gums, blood in urine or stool, severe bruising) to your doctor immediately.
- Maintain a consistent diet, especially regarding foods rich in Vitamin K. Do not make drastic changes to your diet without consulting your doctor.
- Always carry an identification card or wear a medical alert bracelet stating that you are taking warfarin.
Missed Dose Advice
If you miss a dose, take it as soon as you remember on the same day. Do not take a double dose to make up for a missed one. If it's almost time for your next dose, skip the missed dose and continue with your regular schedule. Contact your doctor or pharmacist if unsure.
Driving Precautions
Warfarin does not typically impair driving ability or the ability to operate machinery. However, if you experience significant bleeding episodes, dizziness, or other severe side effects, you should avoid driving or operating machinery and consult your doctor.
Lifestyle Advice
- Avoid activities that carry a high risk of injury or falls, as these can lead to serious bleeding.
- Use a soft toothbrush and an electric shaver to minimize the risk of bleeding from gums or skin.
- Limit alcohol intake, as excessive alcohol can increase the risk of bleeding and affect warfarin's metabolism.
- Discuss any changes in your diet or lifestyle with your healthcare provider, especially regarding new supplements or significant dietary modifications.
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