Dermatology Made Easy is based on the most popular topics from DermNet NZ's vast array of material. The book combines the essential focus of the ‘Made Easy’ book series with the authority and knowledge base of DermNet NZ's unparalleled resources.
Author: Kelson Tu’akoi, Final Year Medical Student, University of Auckland, New Zealand; Chief Editor: Dr Amanda Oakley, Dermatologist, Hamilton, New Zealand, June 2015.
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.
Blood clots are part of a complicated cascade of events, known as haemostasis, that prevents bleeding from an external or internal wound.
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:
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.
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.
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 (NOACs) include:
Compared to warfarin, these novel antiocoagulants:
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,
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).
|Peak plasma time (hr)||36–72||2–3||2.5–4||3|
Suggested guidelines for perioperative management of oral anticoagulant and antiplatelet medication for dermatological surgery are provided by Brown et al (simplified below).
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.
See general guidelines.
Dabigatran may be stopped 12 to 48 hours prior to surgery, if the risk of bleeding is high. Severe surgical bleeding that cannot be stopped with pressure may require reversal using tranexamic acid or, in an emergency situation, using the specific reversal agent, idarucizumab.
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