Warfarin instructions for use
Warfarin is a vitamin K antagonist, an antithrombotic drug of a group of indirect anticoagulants. Reduces the risk of blood clots. It is used in the therapy and prevention of thrombosis, embolism of blood vessels.
Form of issue and composition
Warfarin is available in tablets of 2.5 mg, 3 mg and 5 mg. Tablets are packaged in blisters or in vials.
The main active ingredient is warfarin sodium clathrate.
Auxiliary components: magnesium stearate, calcium hydrogen phosphate, lactose, corn starch, povidone 30, dye.
Pharmacodynamics. Warfarin is a derivative of coumarin. Refers to a group of indirect anticoagulants. Oppresses the production of vitamin K-dependent clotting factors and anticoagulant protein C and S in the liver.
Pharmacokinetics. Warfarin is rapidly absorbed from the digestive tract after ingestion. It is also absorbed through the skin. Virtually completely (97-99%) is associated with blood plasma proteins. Splits in the liver into active metabolites. The half-life period averages 40 hours. 92% of the active substance is excreted in the urine in the form of metabolites, a small amount - in an unchanged form. Penetrates through the placental barrier. The breast milk is excreted in small amounts.
Indications for use
Warfarin is prescribed for the treatment and prevention of thrombosis, embolism of blood vessels. Indications:
- acute and recurrent venous thrombosis;
- pulmonary embolism;
- postoperative thrombosis;
- repeated myocardial infarction;
- Prosthesis of valvular and vascular valves (possible combination with acetylsalicylic acid);
- thrombosis of the coronary, cerebral, peripheral arteries;
- prevention of thrombosis after a heart attack and atrial fibrillation;
- therapy and prevention of transient ischemic attacks and strokes.
Contraindications to the use of Warfarin are:
- pathological changes in blood composition;
- recently received a traumatic brain injury;
- ophthalmological operations;
- extensive surgical operations;
- propensity to bleedings with peptic ulcer, pathologies of respiratory and genitourinary systems;
- cerebrovascular hemorrhages;
- bacterial endocarditis;
- pericarditis (including exudative form);
- severe and malignant hypertension;
- severe renal dysfunction;
- severe liver disorders;
- lack of supervision of the elderly patient;
- extensive anesthesia;
- the holding of a blockade;
- diagnostic measures with the threat of uncontrolled bleeding;
- individual intolerance to warfarin or one of the auxiliary components of the drug;
Dosing and Administration
Dosages of the drug are selected for each patient individually, taking into account indications, indicators of blood coagulability and the effectiveness of the treatment. Warfarin can be given in doses from 2 mg to 10 mg per day. The duration of the course of treatment is also determined by the doctor.
The drug is taken once a day, at the same time.
If the patient is prescribed warfarin for the first time, the initial recommended dose is 5 mg per day for 4 days. Then, depending on the patient's condition and laboratory parameters, a maintenance dose, usually from 2.5 mg to 7.5 mg, is determined.
If the patient has been taking Warfarin earlier, the drug is given the first 2 days at a dosage that is twice the known maintenance dose. Then a maintenance dose is taken for 3 days. On the 5th day, the laboratory parameters are monitored and the maintenance dosage is adjusted.
For children, the initial dosage is 0.2 mg / kg once a day and 0.1 mg / kg for violations of liver function. The drug is prescribed to children only for life indications and is taken under strict medical supervision.
In some cases, the use of Warfarin can provoke the development of undesirable side effects from various body systems. Namely:
- from the coagulation system - hematoma, bleeding, anemia, rarely skin and tissue necrosis caused by local thrombosis;
- on the part of the digestive system - nausea, vomiting, diarrhea and abdominal pain;
- from the liver - increased activity of liver enzymes, cholestasis, hepatitis, jaundice;
- from the cardiovascular system - purple staining of toes, chills, vasculitis , paresthesia;
- from the respiratory organs - tracheal or tracheo-bronchial calcification (rarely, with prolonged intake of Warfarin);
- from the nervous system - fatigue, dizziness and headache, a violation of taste, asthenia;
- dermatological reactions - alopecia, dermatitis, bullous rash;
- allergic reactions - skin rash and itching, hives, swelling, fever.
When an overdose of the drug is marked increased bleeding, bleeding. With light poisoning, it is enough to reduce the dose or to cancel the intake of Warfarin for several days. In acute overdose, sorbents are prescribed. Gastric lavage is not performed because of the risk of bleeding. In severe intoxication, vitamin K is given intravenously (dose 5-10 mg). In life-threatening hemorrhages, a blood transfusion, freshly frozen plasma or a concentrate of prothrombin complex factors is performed.
During treatment Warfarin requires:
- mandatory strict adherence to the prescribed dosage regimen;
- periodic monitoring of blood clotting parameters;
- frequent and regular laboratory monitoring and correction of warfarin doses in patients with congestive heart failure;
- constant monitoring of elderly patients and patients with intellectual disabilities;
- observance of caution during the use of Warfarin in the presence of certain diseases - dysbacteriosis, infectious pathologies, traumas with the threat of internal bleeding, moderate arterial hypertension, vasculitis, severe diabetes mellitus, moderate and severe allergic reactions, anaphylactoid reactions;
- taking into account the high probability of drug interaction when used simultaneously with other drugs.
- in combination with anticholinergic drugs can cause memory impairment, a decrease in the concentration of attention in the elderly;
- in combination with hypoglycemic agents (derivatives of sulfonylureas) enhances their therapeutic effect;
- in combination with ethacrynic acid enhances the diuretic effect, causes the development of hypokalemia;
- in combination with ticlopidine may cause liver damage;
- with caution is prescribed with tricyclic antidepressants, allopurinol, ranitidine, ascorbic acid, tocopherol, terbinafine, dipyridamole, chloral hydrate, disopyramide, felbamate;
- when applied simultaneously with colestyramine, the absorption and bioavailability of warfarin decreases;
- when used simultaneously with cyclosporine, the therapeutic effect of both drugs decreases;
- when taking with phenazone, the level of warfarin in the blood plasma decreases;
- in combination with fluoxetine, vitamin E, trazodone, the effect of warfarin is enhanced;
- reception of a large quantity of alcoholic drinks during treatment provokes an increase in the therapeutic effect of the drug;
- in patients with chronic alcoholism, simultaneous administration of warfarin with disulfiram causes an increase in the therapeutic effect of warfarin;
- Warfarin is incompatible with streptokinase and urokenase.
The anticoagulant effect of warfarin increases and the risk of bleeding increases with simultaneous use with:
- non-steroidal anti-inflammatory drugs, including acetylsalicylic acid;
- antiarrhythmic drugs (quinidine, amiodarone, propafenone);
- antibacterial and antifungal drugs (metronidazole, miconazole, ketoconazole, fluconazole, ciprofloxacin, norfloxacin, clarithromycin, roxithromycin, azithromycin, doxycycline, tetracycline, benzylpenicillin, cefazolin);
- valproic acid;
The anticoagulant effect of warfarin decreases with simultaneous application with:
- inducers of microsomal liver enzymes (barbiturates, carbamazepine, phenytoin);
- diuretics (spironolactone, chlorthalidone);
- preparations of ginseng.
Pregnancy and lactemia
Warfarin easily penetrates the placental barrier, it can provoke fetal hemorrhagic disorders, bone tissue anomalies, optic nerve atrophy and cataract, up to blindness, physical and mental retardation, microcephaly. Therefore, the drug is contraindicated in pregnant women.
With breast milk, warfarin is secreted in an inactive form. When taking the drug as a lactating woman in children, there were no changes in the pattern of coagulation. Accordingly, warfarin can be used during lactation. The effect of Warfarin on the body of preterm neonates has not been studied.
Clinical data on the safety and efficacy of warfarin in children and adolescents (under 18 years) are not available. The decision to prescribe the drug to the child is taken by the doctor. The use of the drug is carried out under strict medical supervision.
Structural analogues of Warfarin (with the same active substance) are drugs: Warfarex, Marevan.
Terms and conditions of storage
The drug is stored in a place protected from sunlight and moisture, inaccessible to children at a temperature below 25 ° C. Shelf life is 3 years or 5 years (depends on the manufacturer). Do not take the pill after the expiry date indicated on the package.
Warfarin tablets 2.5 mg - 80-105 rub.