What are blood thinners (anticoagulants) and how are they used?

Anti-coagulant drugs ensure that certain components of the blood do not stick together so easily. They therefore protect against the formation of blood clots. Colloquially, they are often called “blood thinners”. Since they do not make the blood more fluid, this designation is actually not correct.
We use anticoagulants to reduce the risk of cardiovascular disease caused by blood clots. These include heart attacks, strokes and venous thrombosis. We divide the anticoagulant agents into three groups.
Oral anticoagulants inhibit the formation or action of certain coagulation factors. This group of medicines includes vitamin K antagonists (coumarins) such as the active ingredient phenprocoumon (known to many as the ‘Marcumar’ brand) and so-called direct oral anticoagulants (DOAKs). Oral anticoagulants have a strong effect. I mainly use them to treat atrial fibrillation after insertion of artificial heart valves or after pulmonary embolism.
Anti-platelet drugs such as ASA cause the platelets (platelets) to not clump together so easily. These agents are weaker than anticoagulants. I mainly use them in people who have had a heart attack or stroke.
Heparins also inhibit individual coagulation factors. Since their effect begins faster than the other remedies, they are especially suitable for acute treatment.
Which type of anticoagulant comes into question depends primarily on the underlying disease of a person. But age, concomitant diseases or risk factors for bleeding complications also play a role. Incompatibilities for certain anticoagulants and possible drug interactions may also influence the selection.

Vitamin K antagonists

Vitamin K antagonists such as the active ingredients phenprocoumon and warfarin are highly effective drugs: when used, it takes much longer for the blood to clot. In Germany, phenprocoumon is the most commonly prescribed vitamin K antagonist. Someone knows it too many people as a drug with the trade name Marcumar, but also available as falithrom and phenprogamma.
Vitamin K antagonists are usually taken by people at high risk for strokes, for example. These include people with artificial heart valves, atrial fibrillation and people who have had pulmonary embolism before. Since vitamin K antagonists are available as tablets, they are suitable for long-term use.
The drugs inhibit the formation of certain coagulation factors in the body that are produced in the liver with the help of vitamin K. They displace some vitamin K from the liver, which then produces less coagulation factors. That is why they are also called vitamin K “antagonists” (“antagonists”). They are only fully effective after about two to four days when the coagulation factors already in the blood are broken down by the body.
Although the extent of anticoagulation depends on the dose of the active ingredients used, it can differ from person to person and even in the same person. During treatment it is therefore important to check the coagulation value of the blood regularly.
Normally, vitamin K antagonists should not be used during pregnancy as they can harm the unborn baby. Therefore, it is important for women taking the medication to ensure adequate contraception and to talk to a doctor in good time if they want to have a baby. Even after giving birth, a mother should not use any vitamin K antagonists as long as she is breastfeeding. The active ingredients can enter the body of the child via the breast milk and also inhibit coagulation there.

Interactions of vitamin K antagonists

Vitamin K antagonists have many interactions with other substances – including over-the-counter medicines and herbal products. Hints for possible interactions exist for example for:
  • Antibiotics such as amoxicillin and ciprofloxacin
  • Psychotropic drugs such as citalopram and sertraline
  • Remedy for gastric ulcers such as cimetidine and omeprazole
  • herbal medicines with ginkgo, St. John’s wort or ginseng
  • Painkillers such as ASA and acetaminophen
  • Influence of diet and exercise on the effect
Because the drugs work by displacing vitamin K from the liver, the vitamin K content of the diet also affects its effect. The foods that contain a lot of vitamin K include, for example, cauliflower, broccoli, sauerkraut and beef and pork. However, anyone taking vitamin K antagonists need not eat any other way. Only if someone changes their diet, for example because of a diet, can this affect blood clotting.
Large amounts of alcohol can influence the coagulation ability of the blood and increase the effect of the anticoagulant. However, the occasional consumption of smaller quantities is not a problem. Also, acute and chronic diseases of the gastrointestinal tract can affect the blood clotting and the effect of the drugs.
Physical activity and sports have no direct influence on blood clotting. However, if you take vitamin K antagonists, it makes sense to weigh whether the risk of injury and thus the risk of bleeding in certain sports is not too high.
When changing dietary habits, lifestyle changes or other conditions, it is important to control the blood clotting value more frequently. This allows they to detect fluctuations in good time and to adjust the dose.

Direct oral anticoagulants (DOAKs)

I have approved four more anticoagulants in recent years: apixaban, dabigatran, edoxaban and rivaroxaban. They are also swallowed. The blood clotting value need not be controlled during the application.
To date, the new active substances have only been approved for certain indications: for the prevention of strokes for people with atrial fibrillation and increased risk, and for the treatment or prevention of deep vein thrombosis and pulmonary embolism. Apixaban, dabigatran and rivaroxaban can also prevent thrombosis after insertion of an artificial knee or hip joint.
DOAKs also directly inhibit a certain coagulation factor. Its effect begins after a few hours.
There are still no adequate studies on the use of these agents during pregnancy or lactation, so I must not use them during these periods.


Anti-platelet antiplatelet drugs are weaker than anticoagulants, but have fewer side effects such as bleeding. They are mainly taken by people who have already had a heart attack or stroke to reduce the risk of another heart attack. The most commonly used platelet inhibitor is acetylsalicylic acid (ASA). Other platelet inhibitors include clopidogrel, dipyridamole, prasugrel and ticagrelor.

How do platelet inhibitors work?

Platelet inhibitors inhibit the function of platelets: they prevent them from adhering to injured blood vessels and to each other, thus forming a blood clot. Platelet inhibitors are therefore also called platelet function inhibitors or platelet aggregation inhibitors (of: platelet = platelets, aggregation = stick together, connect).

Interactions of platelet inhibitors

We use ASA not only as a platelet inhibitor but also in higher doses as a painkiller. It can increase the risk of stomach bleeding. This also applies to other analgesics such as diclofenac or ibuprofen. In addition, these drugs may interfere with the anticoagulant effects of ASA. For people who already take ASA for anticoagulation, the analgesic acetaminophen can be a better choice, as it hardly increases the risk of bleeding.

Another group of anticoagulants are the so-called heparins. The coagulation inhibition starts with these agents immediately. Therefore, they are particularly suitable for the acute treatment of venous thrombosis, pulmonary embolisms or heart attacks as well as for the prevention of venous thrombosis in people who need to undergo major surgery.
Heparins lead to a direct and immediate inhibition of certain coagulation factors in the blood. They must be injected under the skin or into a vein for them to work. Since most people find tablets more pleasant than syringes, especially after prolonged use, heparins are generally not used on a long-term basis.

What side effects do blood thinners have?

The medication should not completely switch off the coagulation ability of the blood. Finally, injuries without the blood clotting would otherwise lead to large blood losses. However, taking anticoagulant medication will take longer for the body to close wounds and stop bleeding.
The most common side effects with oral anticoagulants and with platelet inhibitors are bleeding. Slight nose or gum bleeding and bruises on the skin are usually unproblematic. However, major bleeding must be treated quickly. Medical advice is useful for the following signs:
  • strong, persistent nose or gum bleeding
  • large bruises
  • red discolored urine
  • Blood stains in the stool (dark red or black stained chair)
A rare but serious side effect of blood thinners is cerebral hemorrhage. They can be felt by severe, sudden headaches, especially in connection with other problems such as blurred vision, dizziness, paralysis or sensory disturbances. With such signs, it is important to call the emergency doctor immediately.
Some anticoagulants also cause hair loss or rashes. Very rarely, clopidogrel and heparins can cause a strong and threatening reduction in the number of platelets.
When taking vitamin K antagonists, it may be necessary for larger injuries to artificially deliver coagulation factors or vitamin K to the body to speed up blood clotting.
A common measure for the safe use of blood thinners is a drug passport. He is available in the doctor’s office. It states it use what illness for, how it is to be dosed and they can contact which doctor. For example, I can see directly it in emergencies when someone takes blood thinners. This can help prevent complications.

What I should consider before surgery and other procedures?

If a major operation is due, it may be necessary to discontinue or adjust the treatment with blood thinners a few days before. Before an operation or other surgery, such as a gastroscopy, the doctor should therefore be informed in time about the treatment with anticoagulant drugs. In addition, it may be helpful to show the medication pass.
For minor procedures and dental procedures, treatment with blood thinners may not be necessary. But even then it is better to inform the doctor beforehand. He or she can then adjust in time if there should be any problems with the treatment. Also, before spraying or vaccinations, it is important to inform about the treatment with blood thinners. For example, injecting into a muscle in people taking anticoagulant drugs can lead to greater bruising.


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