Overview

If you’ve ever had a heart attack or stroke, or know anyone who has, you’ll understand how difficult and stressful it can be. During the recovery period, it is important to make certain lifestyle changes to prevent further health issues and ensure safe rehabilitation. These changes are fundamental for improving your health and quality of life.

They can involve adjustments to your physical activity, attending cardiac rehabilitation programmes, or taking prescribed medicines.¹ Antiplatelet drugs are one of the commonly prescribed medications used to reduce your chances of having another heart attack or stroke. In this article, we will explain the use of antiplatelet therapy and discuss the benefits and risks of this treatment. 

What are platelets?

Platelets are small blood cells that help form blood clots. These cells play a role in a process called haemostasis. Haemostasis refers to clotting of blood cells, it is the body’s response to an injury, where excessive bleeding is prevented to enable the healing and repair of a wound.

In response to an injury, your platelets will clump together to form a clot. Blood clots are normally beneficial, as they promote wound healing; they act as a natural plug to slow and stop excessive bleeding. This is illustrated in Figure 1.

However, in the case of individuals with coronary heart disease (CAD), blood clots can cause significant problems. People with CAD have narrower coronary arteries; this is a result of a buildup of fatty deposits (plaques). 

These plaques reduce blood flow, limiting the amount of blood that can reach your heart muscle. When the plaque ruptures, the body responds by forming a clot. This blood clot blocks blood flow, leading to a heart attack. Coronary arteries are vital as they supply the heart with blood containing essential oxygen and nutrients. Blockage of these arteries is what ultimately triggers a heart attack, as a result of prolonged deprivation of blood to the heart muscle.¹

Ischaemic strokes also occur following the build-up of fat deposits or blood clots in the brain’s blood vessels. Again, this results in narrowing and blockage of the blood vessels, leading to oxygen and nutrient deprivation of the brain cells.

How does antiplatelet therapy work?

As the name implies, antiplatelet drugs inhibit platelets normal function. In doing so, these drugs prevent platelets from clumping together to form blood clots. Inhibition of blood clot formation allows for normal blood flow within vessels and prevents blockage of your blood supply to vital organs, such as the heart and the brain. In this way, antiplatelet therapy reduces your risk of getting a heart attack or stroke. 

Types of antiplatelet drugs

Aspirin

The most commonly used antiplatelet drug is aspirin which is typically administered as an oral tablet. It is the main drug used for the secondary prevention of heart attacks and is often prescribed for long-term use in low doses. It works by blocking the enzyme, cyclooxygenase. Inhibition of cyclooxygenase makes the platelets less “sticky”, which prevents them from clumping together.²

Please note, that daily low-dose aspirin is not recommended for primary prevention of cardiovascular disease in otherwise healthy people. This guideline was instated following research that reported an increased risk of major bleeding and haemorrhage for healthy people without cardiovascular disease. In these studies, the risk of cardiovascular disease was also not significantly lower than in the control group, suggesting that the benefits of taking aspirin daily did not outweigh the risks.^3,4

Aspirin is also not recommended for those sensitive to the asthmatic effects of aspirin or other non-steroidal anti-inflammatory drugs. Another reason why your doctor may not prescribe you this drug is if you have a medical history of bleeding in the stomach or intestines (this may be due to chronic gastritis).

Adenosine diphosphate (ADP) receptor inhibitors

• Clopidogrel
• Cangrelor
• Ticagrelor
• Prasugrel

ADP receptor inhibitors block ADP-induced platelet aggregation and are administered orally. Similar to aspirin, these inhibitors stop platelets from clumping together.²

Adenosine reuptake inhibitors

Dipyridamole is an adenosine reuptake inhibitor used for secondary prevention of ischaemic stroke and transient ischaemic attacks. It inhibits enzymes involved in blood clotting.²

Glycoprotein platelet inhibitors

• Abciximab
• Eptifibatide
• Tirofiban

This type of antiplatelet drug works by inhibiting glycoprotein IIb/IIIa receptors found on platelets, which prevents your platelets from sticking together. Glycoprotein platelet inhibitors can only be administered intravenously by specialists, therefore they are only prescribed as a short-term therapy.²

Who should be given antiplatelet therapy?

Antiplatelet therapy should be offered to people susceptible to heart attack and stroke. This includes people who have:

• Angina
• Atrial fibrillation
• Coronary heart disease (CHD)
• Peripheral arterial disease (PAD)
• Undergone angioplasty and stent insertion, coronary artery bypass graft (CABG), or heart-valve surgery 

People with cardiovascular disease or with a higher risk of heart attack or stroke have been shown to significantly benefit from antiplatelet therapy. Daily use of low-dose aspirin as secondary prevention is recommended to reduce their risk of a future attack. Antiplatelet therapy is also used to prevent blood clots in the arteries of people who have undergone stent insertion or CABG surgery.

Risks and potential side effects

Due to the nature of how the drugs work, they can potentially exacerbate and increase the risk of major bleeding. Antiplatelet drugs prevent all blood clot formation, this includes the ones your body may need to heal wounds. For example, in the case you experience internal bleeding or a wound on your skin, these drugs will cause excessive bleeding as blood clots are inhibited from forming. 

For this reason, it is vital to consult your healthcare provider before you start antiplatelet therapy. Your doctor will help you evaluate and consider the benefits and risks of choosing this treatment modality. 

Common adverse effects of antiplatelet therapy may include:²

• Aspirin-induced asthma
• Ecchymosis (bruises)
• Haemorrhage
• Nasal polyps
• Nosebleeds
• Shortness of breath (this is a common side effect of ticagrelor use)
• Stomach ache
• Thrombocytopenia (prolonged, heavier bleeding with cuts or menstrual periods) 

If you are experiencing more severe symptoms, this may be indicative of serious problems. Contact your healthcare provider if:²

• You have blood in your urine
• You have blood in your poo
• You are coughing up or vomiting blood
• There is ringing in your ears (tinnitus)
• You have a large, raised bruise (haematoma)

Please note that the list of symptoms (above) is inexhaustive. For a full list see the leaflet enclosed within your medicines packaging, or consult your healthcare provider for further guidance. 

Who should avoid antiplatelet therapy?

You should avoid taking antiplatelet drugs if you:^2,5

• Are pregnant or breastfeeding
• Have a history of high risk of bleeding
• Have a history of gastrointestinal bleeding or stomach ulcers
• Have a bleeding disorder (haemophilia)
• Are taking nonsteroidal anti-inflammatory drugs
• Have thrombocytopenia (low platelet count)
• Have kidney or liver disease

FAQs

What is the most common antiplatelet drug?

The most widely used antiplatelet drug is aspirin. If aspirin is not well tolerated, then clopidogrel may be prescribed instead. Other antiplatelet drugs that are used in combination or as an alternative to aspirin include:

• Prasugrel
• Ticagrelor
• Cangrelor 
• Dipyridamole

What is the difference between a blood thinner and an antiplatelet?

Antiplatelet drugs are a type of blood thinner. “Blood thinner” is a collective term often used synonymously to describe both anticoagulants and antiplatelets. Please note, that although they are similar. Anticoagulants and antiplatelets are distinct and should not be confused with each other. 

Neither anticoagulants nor antiplatelets make the blood “thinner”. They just stop blood clots from forming. They do not break up existing clots either; they can only help to slow down their growth.

Anticoagulants (e.g., heparin and warfarin) slow blood clot formation by targeting the coagulation cascade. Whereas, antiplatelet drugs differ from anticoagulants as they target platelet aggregation instead.⁶ 

Summary

Antiplatelet therapy is a beneficial treatment commonly used to prevent blood clots in people with a higher risk of heart attack or stroke. This includes people who have undergone certain surgeries and people with cardiovascular disease or angina. There are a variety of antiplatelet drugs, in general, they all work by preventing the formation of blood clots.

They do this by stopping platelets from sticking together. However, these medications can potentially worsen your condition as they can increase your risk of excessive bleeding, especially in the gastrointestinal tract. Therefore, always consult your healthcare provider before opting for this treatment.