Antiplatelet drug


An antiplatelet drug, also known as a platelet agglutination inhibitor or platelet aggregation inhibitor, is a member of a class of pharmaceuticals that decrease platelet aggregation and inhibit thrombus formation. They are effective in the arterial circulation, where anticoagulants have little effect.

They are widely used in primary and secondary prevention of thrombotic cerebrovascular or cardiovascular disease.
Antiplatelet therapy with one or more of these drugs decreases the ability of blood clots to form by interfering with the platelet activation process in primary hemostasis. Antiplatelet drugs can reversibly or irreversibly inhibit the process involved in platelet activation resulting in decreased tendency of platelets to adhere to one another and to damaged blood vessels' endothelium.

Choice

A 2006 review states: "...low-dose aspirin increases the risk of major bleeding 2-fold compared with placebo. However, the annual incidence of major bleeding due to low-dose aspirin is modest—only 1.3 patients per thousand higher than what is observed with placebo treatment. Treatment of approximately 800 patients with low-dose aspirin annually for cardiovascular prophylaxis will result in only 1 additional major bleeding episode."

Dual antiplatelet therapy

Often a combination of aspirin plus an ADP/P2Y inhibitor is used in order to obtain greater effectiveness than with either agent alone. This is known as "Dual antiplatelet therapy".

Classification

The class of antiplatelet drugs include:

Prevention and treatment of arterial thrombosis

Prevention and treatment of arterial thrombosis is essential in patients with certain medical conditions whereby the risk of thrombosis or thromboembolism may result in disastrous consequences such as heart attack, pulmonary embolism or stroke. Patients who require the use of antiplatelet drugs are: stroke with or without atrial fibrillation, any heart surgery, Coronary Heart Disease such as stable angina, unstable angina and heart attack, patients with coronary stent, Peripheral Vascular Disease/Peripheral Arterial Disease and apical/ventricular/mural thrombus.
Treatment of established arterial thrombosis includes the use of antiplatelet drugs and thrombolytic therapy. Antiplatelet drugs alter the platelet activation at the site of vascular damage crucial to the development of arterial thrombosis.
Thrombolytic therapy is used in myocardial infarction, cerebral infarction, and, on occasion, in massive pulmonary embolism. The main risk is bleeding. Treatment should not be given to patients having had recent bleeding, uncontrolled hypertension or a hemorrhagic stroke, or surgery or other invasive procedures within the previous 10 days.
When considering these medications and the risk-benefit ratio in the perioperative period, one must consider the risk of stopping the medication and a clot forming versus the risk of bleeding during or after the surgery if medication is continued.
Dentists should be aware of the risk of prolonged bleeding time in patients taking antiplatelet drugs when planning dental treatments that are likely to cause bleeding. Therefore, it is important for dentists to know how to assess patient's bleeding risk and how to manage them.

Assess bleeding risk

Identify the likelihood and risk of dental treatment causing bleeding complications.
Dental procedures unlikely to cause bleedingDental procedures with low risk of post-operative bleeding complicationsDental procedures with high risk of post-operative bleeding complications
Local anaesthesia using aspirating syringe and vasoconstrictorSimple extractions up to 3 teeth with restricted wound sizeExtractions involving surgery, large wound or more than 3 teeth at once
Basic Periodontal examination Incision and drainage of intra-oral swellingsFlap raising procedures
Supragingival plaque, calculus, stain removalSix point full periodontal examinationGingival recontouring
Direct or indirect restoration with supragingival marginsRoot surface debridement and subgingival scalingBiopsies
Orthograde endodonticsDirect or indirect restorations with subgingival margins
Prosthetic procedures
Fitting and adjustment of orthodontic appliances.

Drug toxicity

Antiplatelet drugs effect may be affected by patient's medications, current medical conditions, food and supplements taken. Antiplatelet drugs effect may be increased or decreased. An increase in antiplatelet effect would increase the risk of bleeding and results in prolonged or excessive bleeding. A decrease in antiplatelet effect would reduce the risk of bleeding and potentially increase the thromboembolic risk. Drug toxicity also may increased when multiple antiplatelet drugs are used. Gastrointestinal bleeding is a common adverse event seen in many patients.

Medications

Medications that may increase antiplatelet drugs effect:
Medications that may decrease antiplatelet drugs effect:
Usage of NSAIDS as part of dental management of patients with vascular disease should be discouraged as NSAIDS has antiplatelet effect. Instead, simple analgesics such as Paracetamol, Co-codamol should be of first choice. If NSAIDS is required, dentist should be aware of the risk of bleeding and minimise treatment length.

Medical conditions

Medical conditions that may increase antiplatelet drugs effect:
Chronic kidney failure, liver disease, haematological malignancy, recent or current chemotherapy, advanced heart failure, mild forms of inherited bleeding disorders and idiopathic thrombocytopenic purpura.

Food and supplements

Food and supplements that may increase antiplatelet drugs' effect:
St. John's Wort, Ginkgo biloba, Garlic

Oral antiplatelet drugs available in the UK