Warfarin instructions for use
Warfarin is an antagonist of vitamin K, an antithrombotic agent of the group of indirect anticoagulants. Reduces the risk of blood clots. It is used in the treatment and prevention of thrombosis, embolism of blood vessels.
Release form and composition
Warfarin is available in tablets of 2.5 mg, 3 mg and 5 mg. The tablets are packaged in blisters or in vials.
The main active ingredient is warfarin sodium clathrate.
Auxiliary components: magnesium stearate, calcium phosphate, lactose, corn starch, povidone 30, dye.
Pharmacodynamics. Warfarin is a derivative of coumarin. It belongs to the group of indirect anticoagulants. Inhibits the production of vitamin K-dependent blood clotting factors and anticoagulant proteins C and S in the liver.
Pharmacokinetics. Warfarin is rapidly absorbed from the digestive tract after oral administration. Also absorbed through the skin. Almost completely (97–99%) binds to plasma proteins of the blood. Splits in the liver into active metabolites. The elimination half-life averages 40 hours. 92% of the active substance is excreted in the urine as metabolites, a small amount in unchanged form. It penetrates the placental barrier. In breast milk is excreted in small quantities.
Indications for use
Warfarin is prescribed to treat and prevent thrombosis and blood vessel embolism. Indications:
- acute and recurrent venous thrombosis;
- pulmonary embolism;
- postoperative thrombosis;
- repeated myocardial infarction;
- prosthetic heart valves and blood vessels (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 the blood;
- recent traumatic brain injury;
- ophthalmic surgery;
- extensive surgery;
- tendency to bleeding with peptic ulcer, pathologies of the respiratory and urogenital systems;
- cerebrovascular hemorrhages;
- bacterial endocarditis;
- pericarditis (including exudative form);
- severe and malignant arterial hypertension;
- severe renal impairment;
- severe disorders of the liver;
- lack of observation of the elderly patient;
- extensive anesthesia;
- diagnostic measures with the threat of uncontrolled bleeding;
- idiosyncrasy of 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 the indications, indicators of blood coagulation and the effectiveness of the treatment. Warfarin can be administered in doses from 2 mg to 10 mg per day. The duration of treatment is also set by the doctor.
The drug is taken once a day, at the same time.
If warfarin is administered to a patient 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 is determined, usually between 2.5 mg and 7.5 mg.
If the patient was taking warfarin before, for the first 2 days the drug is administered at a dosage of twice the known maintenance dose. Then 3 days, a maintenance dose is taken. On day 5, laboratory values 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 abnormal liver function. The drug is prescribed to children only for health reasons 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:
- on the part of the blood coagulation system - hematomas, bleeding, anemia, rarely necrosis of the skin and tissues caused by local thrombosis;
- on the part of the digestive system - nausea, vomiting, diarrhea and abdominal pain;
- on the part of the liver - increased activity of liver enzymes, cholestasis, hepatitis, jaundice;
- on the part of the cardiovascular system - purple staining of the toes, chills, vasculitis , paresthesia;
- on the part of the respiratory system - tracheal or tracheal-bronchial calcification (rarely, with long-term use of warfarin);
- on the part of the nervous system - fatigue, dizziness and headache, a violation of taste, asthenia;
- dermatological reactions - alopecia, dermatitis, bullous rash;
- allergic reactions - skin rash and itching, urticaria, edema, fever.
With an overdose of the drug there is increased bleeding, bleeding. In case of mild poisoning, it is enough to reduce the dose or cancel reception of warfarin for several days. In acute overdose, sorbents are prescribed. Gastric lavage is not performed due to the risk of bleeding. When severe intoxication prescribed vitamin K intravenously (dose of 5 - 10 mg). With life-threatening bleeding, blood transfusions, fresh frozen plasma or factors concentrate of the prothrombin complex are performed.
During treatment with warfarin is required:
- mandatory strict patient compliance with the prescribed regimen and dosages of the drug;
- periodic monitoring of blood clotting parameters;
- frequent and regular laboratory monitoring and dose adjustment of warfarin in patients with congestive heart failure;
- constant monitoring of elderly patients and patients with mental disorders;
- caution while taking warfarin in the presence of certain diseases - dysbacteriosis, infectious pathologies, injuries with a 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 interactions with simultaneous use with other means.
- in combination with anticholinergic drugs can cause impaired memory, decreased concentration in the elderly;
- in combination with hypoglycemic agents (sulfonylurea derivatives) enhances their therapeutic effect;
- in combination with ethacrynic acid increases the diuretic effect, causes the development of hypokalemia;
- in combination with ticlopidine can cause liver damage;
- with caution prescribed with tricyclic antidepressants, allopurinol, ranitidine, ascorbic acid, tocopherol, terbinafine, dipyridamole, chloral hydrate, disopyramide, felbamate;
- with simultaneous use of Kolestiramine, the absorption and bioavailability of warfarin decreases;
- with simultaneous use with cyclosporine, the therapeutic effect of both drugs is reduced;
- when taken 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 amount of alcoholic beverages during treatment provokes an increase in the therapeutic effect of the drug;
- in patients with chronic alcoholism, concurrent use of warfarin with disulfiram causes an increase in the therapeutic effect of warfarin;
- Warfarin is incompatible with streptokinase and urokenase.
Anti-coagulant action of warfarin increases and the risk of bleeding increases, while applying with:
- nonsteroidal 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 is reduced when used simultaneously with:
- inducers of liver microsomal enzymes (barbiturates, carbamazepine, phenytoin);
- diuretics (spironolactone, chlorthalidone);
- ginseng preparations.
Pregnancy and lactation
Warfarin easily penetrates the placental barrier, can cause hemorrhagic disorders in the fetus, anomalies of bone tissue development, optic nerve atrophy and cataracts, even blindness, physical and mental retardation, microcephaly. Therefore, the drug is contraindicated in pregnant women.
With breast milk, warfarin is released in an inactive form. When taking the drug by a nursing woman in children, there were no changes in the blood clotting pattern. Accordingly, warfarin can be used during lactation. The effect of warfarin on the body of premature newborns has not been studied.
Clinical data on the safety and efficacy of warfarin in childhood and adolescence (under 18) are not available. The decision on the appointment of the drug to the child takes the doctor. The use of funds is carried out under strict medical supervision.
Structural analogues of warfarin (with the same active ingredient) are drugs: Varfereks, 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. The shelf life is 3 years or 5 years (depends on the manufacturer). Do not take pills after the expiration date indicated on the package.
Warfarin tablets 2.5 mg - 80-105 rubles.