What Is Anticoagulant Therapy

  • Shazia Azim PhD Scholar (Pharmacology), University of Health Sciences Lahore, Pakistan
  • Regina Lopes Senior Nursing Assistant, Health and Social Care, The Open University

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Are we not hearing about people suffering from acute heart problems more in recent years? Many people are using blood thinner pills nowadays. Being on blood thinners reduces the risk of blocked blood vessels that supply blood to vital organs and prevents serious life-threatening problems like heart attack or stroke. Let’s dive into this article for more details on why and how anticoagulation therapy is being given.

Anticoagulation therapy

Blood thinners do not make the blood thin. On the contrary, it prevents the formation of blood clots (thrombus). They are also called anticoagulants. Contrary to its name, blood thinners  Anticoagulation therapy works by either breaking down the already formed clots or preventing the formation of a new one in blood vessels.

Blood clots are crucial to stop bleeding. However, if the clot is unstable or loosened, it travels in the bloodstream and may block blood supply to organs such as the brain, lungs, or heart. That is why anticoagulant therapy is very important. Any disrupted blood supply will cause no or limited oxygen supply making that organ defective or non-functional.

Overview of the blood clotting process

A critical balance between clotting and non-clotting factors is vital to maintain the fluidity of blood. Understanding the series of events involved in the coagulation process helps to get an idea of how anticoagulation therapy works. Coagulation is a complex process involving multiple activating factors and enzyme interactions.1 It can be broadly divided into four major stages:

  • For any damage in our body that causes bleeding (tear of a blood vessel), the endothelial cells on the blood vessel release a factor that mediates platelet aggregation to the damaged area in the vessel wall. 
  • A cascade of many clotting factors and enzymes is activated in the next step to stabilise the platelet plug formed by aggregated platelets. Thrombin (from prothrombin) is a major and active player that converts the circulating soluble fibrinogen to insoluble fibrin which helps in making a perfect meshwork for a stable clot.
  • Once a stable clot is in place, the antithrombin mechanism comes into action to regulate the extent of clot formation and prevent any problems such as thrombosis, inflammation  of blood vessels, and tissue damage
  • Fibrinolysis is the last step during which clots are lysed and cleared with the help of another enzyme called plasmin to ensure proper wound healing and tissue remodelling.2

Not only physical damage, smoking, high blood pressure as well as diabetes can cause a tear or damage to the blood vessels and result in clot formation.

Types of anticoagulants

Anticoagulants are designed to target different stages of the coagulation cascade described above. They can either directly inhibit thrombin or block the conversion of thrombin from prothrombin. In addition, anticoagulants can also work by inhibiting the synthesis and function of vitamin K and related factors. Let us see some of the commonly prescribed anticoagulant drugs and their uses below:


Warfarin is a vitamin K antagonist. It inhibits the action of vitamin K which is essential in the synthesis of different clotting factors. Generally, warfarin is given orally and prescribed to treat conditions such as deep vein thrombosis, pulmonary embolism, and atrial fibrillation. It is also used to prevent blood clot formation in patients with mechanical heart valves.3 

The therapeutic efficacy of warfarin can be counteracted by vitamin K-rich foods, other drugs, and alcohol. Frequent dosage checks and regular monitoring are important to ensure blood clotting time remains within therapeutic range and to rule the risk of bleeding. Specific reversal agents such as vitamin K and prothrombin complex concentrates are used in case of emergencies.


Heparin is a commonly used anticoagulant in clinics. It acts very differently from warfarin by accelerating the action of antithrombin III, which naturally inhibits blood clotting factors. Heparin aids antithrombin III in inactivating thrombin directly and/or blocking the conversion of thrombin from prothrombin.4Generally, heparin is used to prevent the formation of new clots and also the worsening of existing clots in patients with deep vein thrombosis and pulmonary embolism.

In addition, heparin is widely used during surgical interventions related to heart or blood vessels where there is a high risk of blood clot formation. Two different types of heparin are currently in use

  • Unfractionated heparin during surgeries for short-term use
  • Low molecular weight heparin for other out-patient conditions for long-term use.

Regular dose adjustments and close monitoring of activated partial thromboplastin time (time taken for blood clotting) to assess the efficacy of the treatment and to rule out any risk of bleeding disorder. A specific reversal agent is used against heparin in case of excessive bleeding.

Direct oral anticoagulants 

This type of anticoagulant is taken orally and it directly acts on clotting factors either by inhibiting the action of thrombin or by preventing conversion of prothrombin to thrombin.5 Although bleeding is still a potential side effect of direct oral anticoagulants, they do not require regular monitoring. They even have fewer interactions with other drugs and food.

Who needs anticoagulation therapy?

Individuals who are at great risk of developing blood clots are recommended anticoagulation therapy. However, previous medical history and risk factors should be thoroughly assessed before treatment for safety purposes. Some of the clinical conditions for which anticoagulation therapy is commonly recommended are listed below:

Atrial fibrillation 

Atrial fibrillation is a serious heart condition involving the upper chambers of the heart known as atria. It is characterised by poor contraction of atria causing low blood flow. The symptoms include irregular and rapid heart rate. Patients who suffer from this condition are at high risk of developing blood clots, stroke, and other heart-related issues. Anticoagulants are prescribed to reduce the above complications alongside heart rate/ rhythm-controlling medications.6 

Venous thromboembolism 

Venous thromboembolism relates to two highly serious medical conditions called deep vein thrombosis and pulmonary embolism. Deep vein thrombosis involves the formation of a blood clot in any deep vein, most often in the legs or pelvis. The most serious complication of this condition is pulmonary embolism which happens when the clot formed in any of the deep veins dislodges and travels in the bloodstream towards lungs.7 Long-term anticoagulants are prescribed to prevent recurrence and any serious complications.

Mechanical heart valves

Patients with damaged or malfunctioning heart valves are generally given mechanical heart valves. These valves are made of synthetic materials and surgically replaced to mimic the natural valve. Life-long anticoagulants (vitamin-K-based) are generally prescribed for patients with mechanical valves to prevent the risk of blood clots on these synthetic valve surfaces.8  

Post-surgical procedures

Anticoagulants are often prescribed post-joint replacement surgeries to prevent the 

development of blood clots and the subsequent risk of deep vein thrombosis.9 In most of the cases, direct oral anticoagulants are prescribed for effective prophylaxis.


Patients with a history of strokes or who are at high risk of stroke due to high blood pressure, diabetes, or any other factors are prescribed anticoagulants to prevent it. Non-vitamin-K-based anticoagulants are found safer and more effective in such cases.

Cardiovascular diseases

Patients with atherosclerotic cardiovascular diseases (fatty deposits on blood vessels either fully or partially blocking blood flow) and with a history of heart attacks are recommended for anticoagulation therapy.10

Furthermore, anticoagulation therapy is recommended for certain autoimmune conditions like antiphospholipid syndrome which has a high risk of developing clots. Also, for some cancer patients, especially during chemotherapy to prevent developing cancer-related thrombosis and individuals with antithrombin deficiency.

Monitoring and management

Anticoagulant prescription is generally individualised based on the patient's age, weight, diet, other medications, and other prevailing medical conditions. The doctor determines the choice of anticoagulant and its dosage and duration after a thorough analysis of the patient's medical history. Patients who are undergoing anticoagulant therapy must adhere to the medication regimen for its effectiveness. In addition, regular follow-up protocols are recommended to prevent potential complications.

Side effects

Patients undergoing anticoagulant therapy have to closely monitor any severe and abnormal signs and symptoms related to bleeding. They should promptly be reported and immediate medical attention must be obtained. 

However, the following side effects are common

  • Blooding in urine
  • Passing black poop (blood in poop)
  • Easily bruised
  • Bleeding gums and nose
  • Heavy periods in women
  • Vomiting or coughing up blood


Anticoagulant therapy is a lifesaver for individuals who are at great risk of blood clotting disorders. Certain life-threatening medical conditions like atrial fibrillation, deep vein thrombosis, and pulmonary embolism are effectively treated using anticoagulants. Additionally, acute heart problems, stroke, and other diseases/conditions that lead to thrombosis are effectively prevented. Although anticoagulation therapy poses a high range of risks, the risks outweigh the potential benefits. Patients must follow regular monitoring and dietary considerations for effective outcomes of the therapy.


  1. Palta S, Saroa R, Palta A. Overview of the coagulation system. Indian J Anaesth [Internet]. 2014 [cited 2024 Mar 2];58(5):515–23. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4260295/
  2. Harter K, Levine M, Henderson SO. Anticoagulation drug therapy: a review. West J Emerg Med [Internet]. 2015 Jan [cited 2024 Mar 2];16(1):11–7. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4307693/
  3. Patel S, Singh R, Preuss CV, Patel N. Warfarin. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 [cited 2024 Mar 2]. Available from: http://www.ncbi.nlm.nih.gov/books/NBK470313/
  4. Warnock LB, Huang D. Heparin. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 [cited 2024 Mar 2]. Available from: http://www.ncbi.nlm.nih.gov/books/NBK538247/
  5. Julia S, James U. Direct oral anticoagulants: a quick guide. Eur Cardiol [Internet]. 2017 Aug [cited 2024 Mar 2];12(1):40–5. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6206466/
  6. Katritsis DG, Gersh BJ, Camm AJ. Anticoagulation in atrial fibrillation – current concepts. Arrhythm Electrophysiol Rev [Internet]. 2015 Aug [cited 2024 Mar 2];4(2):100–7. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4711523
  7. Weitz JI, Prandoni P, Verhamme P. Anticoagulation for patients with venous thromboembolism: when is extended treatment required? TH Open [Internet]. 2020 Dec 23 [cited 2024 Mar 2];4(4):e446–56. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7758152/
  8. Catterall F, Ames PR, Isles C. Warfarin in patients with mechanical heart valves. BMJ [Internet]. 2020 Oct 15 [cited 2024 Mar 2];371:m3956. Available from: https://www.bmj.com/content/371/bmj.m3956
  9. Tun HN, Kyaw MT, Rafflenbeul E, Suástegui XL. Role of direct oral anticoagulants for postoperative venous thromboembolism prophylaxis. Eur Cardiol [Internet]. 2022 May 13 [cited 2024 Mar 2];17:e11. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9127635/
  10. Schäfer A, Flierl U, Bauersachs J. Anticoagulants for stroke prevention in heart failure with reduced ejection fraction. Clin Res Cardiol. 2022 Jan;111(1):1–13.

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