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Anticoagulants and antiplatelet agents

Author: Kelson Tu’akoi, Final Year Medical Student, University of Auckland, New Zealand; Chief Editor: Dr Amanda Oakley, Dermatologist, Hamilton, New Zealand, June 2015.

Their relationship to dermatological surgery

What are anticoagulants and antiplatelet agents?

Anticoagulants and antiplatelet agents are commonly known as "blood thinners", although strictly speaking, they do not thin the blood. They are used to reduce excessive blood clot formation.

How are blood clots formed?

Blood clots are part of a complicated cascade of events, known as haemostasis, that prevents bleeding from an external or internal wound.

What happens if clotting is excessive?

Excessive clotting forms a thrombus, which can completely block a blood vessel and stop normal blood flow. This is known as thrombosis.

A portion of the thrombus can become dislodged (an embolus) and can travel via the blood vessels to block a smaller vessel.

Blood clots which form in arteries are mainly composed of platelets with a small amount of fibrin. They lead to:

Blood clots which form in the larger veins are mainly composed of fibrin, with a small amount of platelets. They lead lead to:

Why do thrombosis and embolism occur?

Thromboembolic disease occurs for genetic and acquired reasons. These may include:

Patients prone to blood clots may be prescribed one or more oral anticoagulants and antiplatelet drugs to reduce their chances of stroke, heart attack and deep venous thrombosis.

The level of antiplatelet/anticoagulant needs to be within a desirable range to reduce the risk of excessive bleeding.

More about antiplatelet agents

Antiplatelet agents inhibit the production of thromboxane. They are mainly used to prevent stroke and heart attack. The most common antiplatelet agent prescribed is a small dose of aspirin (Aspec®, Cartia®, Cardiprin® and others). Other antiplatelet agents include:

Aspirin irreversibly inhibits cyclooxygenase-1, which is needed for prostaglandin and thromboxane synthesis. It has a long half-life.

Clopidogrel, prasugrel, ticagrelor and ticlopidine antagonise the ADP receptor, interrupting platelet activation and cross-linking. These have shorter half-lives.

More about anticoagulants

Anticoagulants are used mainly to treat and prevent venous thrombosis, and to prevent the complications of atrial fibrillation and artificial heart valves. Warfarin is a synthetic derivative of the plant material, coumarin. Use of warfarin (Coumadin®, Maravan®) for anticoagulation began with its approval in 1954, and it has been instrumental in lowering morbidity and mortality associated with thrombotic conditions. Warfarin:

Phenprocoumon (Marcoumar®, Marcumar®, Falithrom®) is used instead of warfarin in some countries, eg Germany.

Novel oral anticoagulants include:

Compared to warfarin, these novel antiocoagulants:

Natural antiplatelet agents and anticoagulants

Some foods, supplements and natural medicines have antiplatelet and anticoagulant activity, including garlic, ginger, ginkgo, dong quai, feverfew, fish oil, vitamin E and many others. Good quality laboratory and human studies have not been performed on these agents and they are unregulated. Food supplements and herbal medicines with uncertain effect on blood clotting should be avoided when taking prescribed antiplatelet and anticoagulant medication because the combination could be dangerous.

Other foods and food supplements contain vitamin K, for example cabbage, Brussels sprouts, broccoli, asparagus and many other green vegetables. These can unpredictably reduce the effectiveness of antiplatelet and anticoagulant drugs,

How do antiplatelet agents and anticoagulants affect dermatological surgery?

Patients taking antiplatelet agents and anticoagulants have an increased risk of bleeding, particularly after trauma. Dermatological surgery in these patients may lead to complications such as:

But, if patients stop their anticoagulants prior to surgery, they face complications associated with thrombosis. This presents a dilemma – should anticoagulation be stopped or continued for dermatologic surgery?

In the past, dermatological surgeons were in favour of interrupting anticoagulants to reduce the risk of bleeding—warfarin increases the surgical bleeding risk ~7–9 fold. However:

It has become clear that discontinuation of anticoagulants can lead to serious thromboembolic events:

Limited data on dabigatran indicates that it follows a similar pattern to warfarin.

As the risks of thromboembolism outweigh the risk of bleeding, it is now recommended that anticoagulants be continued in low-risk operations, such as those encountered in dermatology. This recommendation may differ on a case by case basis. In the event of discontinuing a medication, pharmacokinetic and pharmacodynamic factors need to be considered to optimise the timing (see table below).

Anticoagulant pharmacokinetic properties
WarfarinDabigatranRivaroxabanApixaban
Half-life (hr) 20–60 13–17 5–9 10–14
Peak plasma time (hr) 36–72 2–3 2.5–4 3
Elimination 92% renal
8% faecal
80% renal
20% faecal
66% renal
33% faecal
27% renal
63% faecal
Metabolism Hepatic Hepatic Hepatic Hepatic

General guidelines for anticoagulant and antiplatelet medication during skin surgery

Suggested guidelines for perioperative management of oral anticoagulant and antiplatelet medication for dermatological surgery are provided by Brown et al (simplified below).[3]

Warfarin

Aspirin/Non-steroidal anti-inflammatory drugs (NSAIDs)

Aspirin (10 days) or NSAIDs (3 days) may be discontinued prior to the procedure ONLY if the medication is for primary prevention of stroke or heart attack (ask your doctor), headaches or pain. They may be resumed 3 days after the procedure.

Other anticoagulants and antiplatelet agents

See general guidelines.

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