Contents
Warfarin is a medicine that acts as an anticoagulant. vitamin K antagonist. It is an orally administered coumarin derivative. The action of warfarin allows it to be used in the treatment of, inter alia, deep vein thrombosis, prevention of repeat myocardial infarction and stroke. What is the mechanism of action of warfarin? What are the possible side effects?
Form, dose, packaging: tablets; (3: 5) mg; pack of 100
Availability category: Rp – prescription drug
Active substance: warfarin
Warfarin – action
As an anticoagulant drug, warfarin lowers the blood density by blocking vitamin K from being converted to its reduced form. The reduced form of vitamin K is necessary for the activation of some blood clotting factors (VII, IX, X) produced in the liver. These factors undergo appropriate chemical reactions that activate them. The presence of vitamin K is essential for the proper course of the processes. This process maintains physiological coagulation processes, preventing bleeding out. The therapeutic effect of warfarin appears about 5 days after taking the first dose.
Warfarin – indications for use
The indications for the use of warfarin include: thromboembolism, deep vein thrombosis, prevention of recurrent myocardial infarction or stroke, or pulmonary embolism.
Warfarin – dosage
Oral dosage of warfarin is determined individually on the basis of the INR (International Normalized Ratio) value. The higher the value, the thinner the blood and the longer the clotting time. The INR test allows to determine the state of the coagulation system, as well as to check the effectiveness of anticoagulants. If your INR is less than 1,4, standard dosing includes 10 mg of warfarin for the first three days. On the following day, the INR value is tested and depending on the result, the dosage of warfarin is increased or decreased. In patients struggling with protein S or C deficiency, it is recommended to take 3 mg of warfarin daily for the first 5 days of therapy. On the fourth day, the INR should be determined. It is important that you take warfarin exactly as prescribed by your doctor.
Warfarin – contraindications
As for contraindications to the use of preparations containing warfarin, the list is quite long. The drug should not be taken by people who suffer from impaired blood clotting in the course of, among others: thrombocytopenia, haemophilia, von Willebrand’s disease, disorders of the proper functioning of platelets. Warfarin should not be taken by patients suffering from: liver cirrhosis, aneurysms within the brain (due to the risk of bleeding inside the skull), unregulated blood pressure surges, gastric and duodenal ulcers (higher risk of perforation and gastrointestinal bleeding). In addition, warfarin is contraindicated in people abusing alcohol, suffering from various types of psychotic conditions (due to the possibility of skipping doses and non-compliance with the recommendations of the attending physician). The drug should also not be taken by people who are hypersensitive to warfarin.
Warfarin – interactions
Warfarin is a drug whose metabolism takes place in the liver with the participation of cytochrome P450 enzymes. Its effect can be enhanced by the simultaneous administration of these therapeutic agents, which are also metabolized by the enzymes mentioned. The increased effect of warfarin means it increases its anticoagulant properties, increases blood thinning and the risk of haemorrhage. The INR parameter may also be distorted, which may make the treatment ineffective and inappropriate. Certain medications can inhibit the effect of cytochrome P450, which may lead to a reduction in blood levels of warfarin and its effect. Therefore, before taking warfarin, inform your doctor about any drugs you are taking that have the potential to have an effect on cytochrome P450 enzymes. These include: phenytoin, rifampicin, omeprazole, cimetidine, fluoxetine, paroxetine, topiramate, ketoconazole, ritonavir, metronidazole, amiodarone, erythromycin, clarithromycin. Warfarin should not be taken with grapefruit and cranberry juices. Preparations containing warfarin should not be used with: acetylsalicylic acid, ticlopidine, clopidogrel, penicillins.
Warfarin – warnings
Warfarin should be taken with caution in combination with other drugs, herbal preparations and dietary supplements, e.g. vitamins A and E, ginkgo leaf, angelica root, St. John’s wort. The drug should not be taken by women in the first trimester and 9 months of pregnancy. The INR level should be determined prior to a planned surgery.
Warfarin – side effects
The most common side effects during the use of warfarin include: bleeding, nausea, vomiting, much less often: tracheal calcification, priapism (persistent erection), cholesterol embolism.