Warfarin Pharmacology


About Warfarin
Synthetic coumarin derivative , Vitamin K Antagonist, Anticoagulant.
Mechanism of Action of Warfarin
It exerts it`s pharmacological action by inhibiting regeneration of active hydroquinone from vitamin K and also behaves as a competitive antagonist of vitamin K. Thus the drug interacts with synthesis of vitamin K derived clotting factors (factors; II, VII, IX, and X.) in a dose dependent manner and reduce their plasma levels. Vitamin K-hydroquinone is required for final step of gama-carboxylation of descarboxy forms of these factors. This carboxylation is essential for the ability of the clotting factors to bind Ca2+ and to get bound to phospholipid surfaces and ultimately involve in coagulation cascade.
Pharmacokinets of Warfarin
Absorption: Well absorbed orally.
Distribution: Widely distributed in a protein bound form and crosses the placental barrier.
Metabolism: Metabolized in the liver by hydroxylation in to inactive metabolites.
Excretion: Excreted through urine. Onset of action: 6 to 12hours.

Onset of Action for Warfarin
Duration of Action for Warfarin
3 to 6 days
Half Life of Warfarin
36 to 48 hours
Side Effects of Warfarin
1. Haemorrhage
2. Ulceration
3. Gastrointestinal disturbances
4. Nausea
5. Vomiting
6. Diarrhoea
7. Dermatitis
8. Hypersensitivity reactions
9. Urticaria
10. Rash
11. Reversible alopecia
12. Liver diseases
13. Pancreatitis
Contra-indications of Warfarin
1. Hypersensitivity to the drug
2. Bleeding disorders
3. Ulceration of gastrointestinal tract
4. In sub acute bacterial endocarditis
5. Severe hypertension
6. Increased capillary permeability
7. Cerebrovascular haemorrhage
8. Recent eye brain or spinal cord surgery
9. Abortion
10. Labour
11. Alcoholism
12. Lumbar puncture
13. Vitamin K deficiency
14. Renal impairment
15. Hepatic impairment

Special Precautions while taking Warfarin
If haemorrhage occurs stops the drug use and monitor prothrombin time.
Use with caution in following conditions:
1. Hepatic diseases
2. Renal diseases
3. Gastrointestinal tract disorders
4. Hypertension
5. Heart failure
6. Severe diabetes
7. Infectious diseases
8. Recent surgery
9. Other risks of haemorrhage

Pregnancy Related Information
Old Age Related Information
Use with caution
Breast Feeding Related Information
Use with caution
Children Related Information
Indications for Warfarin
1. Thromboembolism,
2. Pulmonary embolism
3. Transient ischemic attack
4. Atrial fibrillation
5. Rheumatic heart disease
6. Deep vein thrombosis

Interactions for Warfarin
Drugs that increase the anticoagulant effect of warfarin by unknown or complicated mechanisms: Acetaminophen, Beta blockers, Androgens, Clofibrate, Corticosteroids, Cyclophosphamide, Disulfiram, Erythromycin, fluconazole, Gemfibro-zil, Glucagon, Hydantoins, Propoxyphene, Isoniazid, Miconazole, Ketoconazole, Quinolone, sulfonamides, tamoxifen, Thyroid hormones.
Drugs that increase the anticoagulant effect of warfarin by inhibition of hepatic metabolism: Amiodarone, chloramphenicol, Ifosamide, Cimetidine, Lovastatin Metronidazole, Omeprazole, Phenylbutazone, Propafenone, Quinine, Quinidine, sulphamethoxazole, trimethoprim, sulfinpyrazone.
Drugs that enhance efficacy of warfarin by displacement from binding sites: Chloral hydrate, Loop diuretics, Nalidixic acid.
Drugs that enhance anticoagulant effects of warfarin due to interference with Vit. K: Aminoglycosides, Mineral oil, tetracyline, Vit. E.
Drugs that enhance efficacy of warfarin due to effects on platelet function: Cephalosporins, Diflusinal, NSAIDs, Penicillins, salicylates.
Drugs that decrease anticoagulant effect of warfarin by unknown mechanism: Vitamin C, Griseofulvin, Sucralfate, Trazodone, Dicloxacillin, Nafcillin.
Drugs that decrease the anticoagulant effects of warfarin due to induction of the hepatic microsomal enzymes: Aminoglutethimide, Barbiturates, Carbamazepine, Rifampicin, Glutethimide, Etretinate.
Drugs that decrease the anticoagulant effect of warfarin due to various mechanisms: cholestyramine, oral contraceptives, estrogens, thiopurines, Spironolacetone, Vit.K, thiazide diuretics.
Typical Dosage for Warfarin
Start with 5mg daily. Then increases the dosage up to 15mg; based on prothrombin time and international normalized ratio.
Maintenance dosage: 2 to 10mg daily.

Schedule of Warfarin
Storage Requirements for Warfarin
Store at room temperature in a light resistant container.
Effects of Missed Dosage of Warfarin
Take the missed dose as soon as noticed and if it is the time for next dose then skip the missed dose. Continue the regular schedule. Do not double the dose.
Effects of Overdose of Warfarin
In minor haemorrhage stoppage of drug is adequate as a treatment measure. In more advanced haemorrhage administration of Phytonadione (vitamin K1) is required. In severe haemorrhage administer fresh frozen plasma or blood.

Home Delivery for Warfarin in Your City

Medicine India is just a publishing medium for medicine related information and does not provide services or sales of medicines including warfarin.

However, we do publish a comprehensive directory of Pharmacies, Chemists and Druggists in cities all over India. You can use this directory to find the medicine stores in your city (or area) that provide home delivery services for warfarin and other medicines and health products. Home delivery services for warfarin may be free or they may cost you depending on the pharmacy and the minimum order requirements. It would be best to get this clarified while placing the order.

Please be aware that you should take warfarin only if a doctor has recommended or prescribed it. Some or all pharmacies who provide a home delivery service for medicines might insist on a prescription for warfarin before they complete the sale. You can get this information while placing the order for warfarin with the pharmacy.

Warfarin is a generic medicine name and there are several brands available for it. Some of the brands for warfarin might be better known than warfarin itself. If the pharmacy that's willing to deliver medicines to your home doesn't have warfarin in stock, you can ask for one of the branded alternatives for warfarin.