Vitamin K antagonists

Vitamin K antagonists like the active ingredients phenprocoumon and warfarin are highly effective medications: When people use them, it takes a lot longer for their blood to clot. Phenprocoumon is the most frequently prescribed vitamin K antagonist in Germany. Many people know it under its trade name Marcumar, but it’s also available as Falithrom and Phenprogamma.

Vitamin K antagonists are usually taken by people who have a high risk of stroke. They include people with artificial heart valves, atrial fibrillation and people who have had pulmonary embolism. Vitamin K antagonists are particularly suitable for long-term use because they can be taken as tablets.

They stop certain clotting factors that are produced in the liver using vitamin K from forming in the body. They do that by removing some of the vitamin K from the liver, which is why they’re called vitamin K “antagonists.” They only start to take full effect after two to four days once the clotting factors already in the blood have been broken down.

Although the strength of the anti-clotting effect does depend on the dose, it can also vary greatly from person to person, and even over time in the same person. It’s therefore important for the blood's clotting ability to be regularly monitored during treatment.

Pregnant women are usually not allowed to take vitamin K antagonists because they can be harmful to unborn babies. So it's important that women who are taking these medications make sure that they use effective contraception and talk to their doctor if they are planning to get pregnant. Women should also avoid taking vitamin K antagonists while they are still breastfeeding. The active ingredients can enter the child's bloodstream via breastmilk and then also stop their blood from clotting.

Direct oral anticoagulants (DOACs)

Another four anticoagulants have been approved in recent years: apixaban, dabigatran, edoxaban and rivaroxaban. They are also taken orally. When using them, your blood clotting doesn’t need to be monitored.

So far the new drugs have only been approved for the following: Prevention of stroke in people with atrial fibrillation who are high-risk, and treatment or prevention of deep vein thrombosis (DVT) and pulmonary embolism. Apixaban, dabigatran and rivaroxaban are also approved for the prevention of thrombosis after fitting an artificial knee or hip.

DOACs also immediately inhibit a certain clotting factor. They start to take effect after just a few hours.

There isn’t enough research on their use in pregnant or breastfeeding women, so women who are pregnant or breastfeeding should not take them.

Antiplatelets

Antiplatelets (platelet aggregation inhibitors) are weaker than anticoagulants, but side effects such as bleeding are also less common. They are mainly taken by people who have previously had a heart attack or stroke, in order to lower the risk of another attack. The most commonly used antiplatelet is acetylsalicylic acid (ASA). Other antiplatelet drugs include clopidogrel, dipyridamole, prasugrel and ticagrelor.

Heparins

There is another group of anticoagulants called heparins. These products have an immediate anti-clotting effect. That makes them especially suitable for acute treatment of venous thrombosis, pulmonary embolism and heart attacks as well as for prevention of venous thrombosis in people who have to have major surgery.

Heparins directly and immediately inhibit certain clotting factors in the blood. They have to be injected below the skin or into a vein to be effective. Because most people who regularly have to take long-term medication prefer to take tablets rather than inject medication, heparins are generally not used for long-term treatment.

What side effects do blood thinners have?

The medications are not supposed to stop blood from clotting completely. After all, if the blood didn’t clot at all, injuries would lead to major blood loss. But if you are on anti-clotting medication, it does take longer for your body to close wounds and stop any bleeding.

Bleeding is the most common side effect of oral anticoagulant and antiplatelet medications. Light nose bleeds, gum bleeding or bruises on the skin are generally not a problem. But heavier bleeding has to be treated quickly. You should consult a doctor if you notice any of the following:

• Heavy, persistent bleeding from the nose or gums
• Large bruises
• Red-colored urine
• Blood in stool (dark red or black stool)
• Blood in vomit

Strokes are a rare, but very severe side effect of blood thinners. A very strong and sudden headache is a sign of such bleeding, especially if it occurs together with other problems like trouble seeing, dizziness, paralysis or numbness. If these kinds of symptoms occur, it is important to call an ambulance right away (112 in Germany).

Some anticoagulants can cause hair loss or rashes. In very rare cases clopidogrel and heparins can reduce the number of blood platelets to a dangerously low level.

If you have a more serious injury while using vitamin K antagonists, you might need synthetic clotting factors or vitamin K so that your blood clots faster.

One common way to make the use of blood thinners safer is to have a medical ID card. They are available from doctors’ practices in Germany. The card includes information about which illness the medication is taken for, what dosage needs to be taken and which doctor ought to be contacted. In an emergency that information is then on hand immediately. This can help to prevent complications.

What should be kept in mind before surgery and other procedures?

If you’re due to have major surgery, it can be necessary to stop taking or adjust your blood thinners a few days beforehand. Before having surgery or another procedure such as a gastroscopy you should make sure that the doctor knows if you are taking anti-clotting medication in advance. It can also be helpful to show them your medical ID card.

You don’t necessarily always have to stop taking blood thinners before smaller procedures and dental treatment. But even then it’s better to let your doctor know beforehand. That gives the doctor the chance to prepare in case any problems do occur during the treatment. It’s also important that you make it known that you’re taking blood thinners before injections or vaccinations. This is because, for example, an injection into a muscle could cause more severe bleeding if you’re using anti-clotting medication.

Sources

• Ageno W, Gallus AS, Wittkowsky A, Crowther M, Hylek EM, Palareti G. Oral anticoagulant therapy: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines. Chest 2012; 141(2 Suppl): e44S-e88S. [PMC free article: PMC3278051] [PubMed: 22315269]
• Deutsche Gesellschaft für Kardiologie (DGK), European Society of Cardiology (ESC). Pocket-Leitlinie: Management von Vorhofflimmern. Grünwald: Börm Bruckmeier; 2016.
• Eikelboom JW, Hirsh J, Spencer FA, Baglin TP, Weitz JI. Antiplatelet drugs: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines. Chest 2012; 141(2 Suppl): e89S-e119S. [PMC free article: PMC3278069] [PubMed: 22315278]
• Kasper DL, Fauci AS, Hauser SL, Longo DL, Jameson JL, Loscalzo J. Harrison's Principles of internal medicine. New York: McGraw Hill; 2015.
• Mutschler E, Geisslinger G, Menzel S, Ruth P, Schmidtko A. Pharmakologie kompakt: Allgemeine und Klinische Pharmakologie, Toxikologie. Stuttgart: Wissenschaftliche Verlagsgesellschaft; 2016.
• Weitz JI, Eikelboom JW, Samama MM. New antithrombotic drugs: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines. Chest 2012; 141(2 Suppl): e120S-e151S. [PMC free article: PMC3278067] [PubMed: 22315258]

• IQWiG health information is written with the aim of helping people understand the advantages and disadvantages of the main treatment options and health care services.

  Because IQWiG is a German institute, some of the information provided here is specific to the German health care system. The suitability of any of the described options in an individual case can be determined by talking to a doctor. We do not offer individual consultations.

  Our information is based on the results of good-quality studies. It is written by a team of health care professionals, scientists and editors, and reviewed by external experts. You can find a detailed description of how our health information is produced and updated in our methods.