Anti Platelet Drugs Preventing Aggregation Biology Essay


Anti-platelet drugs are drugs used to prevent platelet aggregation and prevent heart disease or stroke. Blood clotting factors are normal in the body to heal injury and wounds where it stops the blood from exiting the body. Usually platelet aggregation is a good thing; but in cases where platelets form in the blood vessels, it interferes in the way of smooth flow of RBC's in the blood vessels, and causes the RBC's to clog and stops the flow of blood back to or from the heart, and therefore causes any form of heart disease.

There are things that increase and decrease platelet aggregation in the body; henceforth, factors that increase or decrease formations of a blood clot or heart diseases.

Factors that increase platelet aggregation are such as:

- Thromboxane A2 (TXA2)

- Adenosine Di-Phosphate (ADP)

- Serotonin 5-HT2 receptors

- GP IIb/IIIa receptors

Factors that decrease platelet aggregation are such as:

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- Prostacyclin (PGI2)

- cAMP

- cGMP

So from these factors, we can gather around the types of anti-platelet medication that can be used to prevent strokes, clots, and attacks.

Some main types of anti-platelet agents are:

↓ Thromboxane A2 - synthesis

ADP - receptor blockers

Selective 5-HT2 antagonist

GP Iib/IIIa receptor blockers

Prostacyclin (PGI2) analogues



The 5 main types we will discuss are:

↓ Thromboxane A2 - synthesis

ADP - receptor blockers


GP IIb/IIIa receptor blockers

Prostacyclin (PGI2) analogues

↓Thromboxane A2 Synthesis

One of the main medication that inhibits thromobxane A2 synthesis is aspirin; its chemical name is acetylsalicylic acid.


Aspirin works by several mechanisms; it prevents production of prostaglandins and thromboxanes. This is done by its ability to irreversibly inactivate the cyclooxygenase enzyme, also known as PTGS enzyme. This enzyme in our body is required for production of prostaglandins and thromboxane; to stay on course, thromboxane is the cause for blood clot formation. So when we block the synthesis for thromboxane, it reduces platelet aggregation, and therefore prevent further diseases.

On a side note, prostaglandins are hormones that are part of trasnmission of pain signals to the brain, fixation of the hypothalmic thermostat, and inflammation.

Another mechanism is inhibiting COXI and COXII - therefore called non-selective COX inhibitors - also called Prostaglandins I and Prostaglandins II. Due to inhibiting COX II, it has an anti-inflammatory effect.

Moreover, aspirin has some some contraindications that we must be aware of. People with allergies to ibuprofen or naproxen, or who have salicylate intolerance, should not take aspirin. Most importantly, aspirin should not be taken if you are a child/teenager with the chicken pox or the influenza - this will cause rey's syndrome and can be fatal. Finally, if you are someone who has bleeding problems, or bleed severly in a bad state, or have a condition called hemophillia, aspirin should be avoided to prevent severe blood loss.

The side effects of aspirin are just as cautious as any other medication; we all know that everyone's system can respond differently to a medication, so we must all be careful. This aspirin medication can cause side effects such as, heartburn, nausea, stomach problems, in which you can take pepto bismol. If severe side effects occur such as, allergic reactions, irregular color stools, bruising, vomiting, or anything very severe, this must seek the attention of a medical doctor.

Finally, aspirin is used for many symptoms. Because aspirin is a non selective COX inhibitor, it is said to be anti-inflammatory drug; as well as an analgesic. Aspirin relieves pain, headaches, a cold, sore throat, and is used to reduce the fever. Aspirin is also used as a blood thinner, so it is classified as an anti-platelet in which it prevents heart diseases or any kind of stroke.

ADP - receptor blockers

One of the main drugs that work as an ADP - receptor blocker is called plavix; its generic name is called clopidogrel.


Plavix is anti-platelet agent that works as an ADP-receptor blocker; Mode of action of clopidogrel

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As we see in this diagram, we understand that clopidogrel works as an inhibitor of ADP - induced platelet aggregation. It is important to mention that plavix is a non-competitive inhibitory that binds irreversibly to the platelet membrane receptors. What is very interesting is once the platelets are shown to plavix, they are affected until their death, which is roughly 7 to 10 days. Plavix does not work on COX and can as well inhibit induced platelet aggregation

ADP binding is necessary for activation of the GPIIb/IIIa receptor, which is the binding site for fibrinogen. Fibrinogen links different platelets together to form the platelet aggregate. Clopidogrel thus ultimately inhibits the activation of the GPIIb/IIIa receptor, its binding to fibrinogen and further platelet aggregation.

Moving on, Plavix should not be used if the patient is allergic to any of the medicinal ingredients produced in the drug. Also, if a patient has a bleeding disorder such as an ulcer or bleeding in the brain hemisphere, plavix should not be taken. And finally, plavix should not be taken if a patient is taking any fungal medications such ketoconazole, and any proton pump inhibitors.

Furthermore, the side effects to plavix are very similar to aspirin, with a few more to keep in mind as plavix is a more potent anti-platelet agent then aspirin. Plavix has minor side effects such as easy bruising, minor bleeding; it can become severe if allergic reactions occur such as rash, itchiness, difficult in breathing, eye bleeding, blurry vision, severe, constant headaches that can lead to migraines. If any of these symptoms occur, its usually a sign that shows plavix is not the drug of choice for this patient, even though it is the drug of choice for treatment.

Finally, plavix has many uses, primarily as an anti-platelet as we have already said before. Plavix, like aspirin, reduces any risk for strokes, heart diseases, or any attacks; it only reduces the risks on patients who have had a history of any heart diseases. Patients who have had any history of unstable angina can also use plavix. One thing that is important to know about plavix is that it is a platelet aggregation inhibitor. It works on the body by slowing or stopping platelets from sticking to blood vessels or any injured tissues.


Another method of an anti-platelet agent, is a drug that is classified under ↑cGMP, such as Nitrates. An example of a nitrate is nitroglycerin - its brand name is Nitro-Dur.


Nitroglycerin is a very widely used drug that is used mainly as a vaso dilator. The main important thing about any nitrates is its mechanism of action. When nitroglycerin is given to the patient, mostly through transdermal patches, it releases nitrous oxide in exchange for sulfur. Once this nitrous oxide is released, it increases the soluble guanylate cyclase enzyme, which then leads to increasing the cyclic GMP, finally decreasing platelet aggregation and therefore causing vasodilatation and causing the antiplatelet effect. What's important to know is that cGMP is a cyclic nucleotide derived from guanosine triphosphate. CGMP is a regulatory nucleotide, most importantly known for its relaxing effect in smooth muscles and blood vessels. When activated, or stimulated, it relaxes the blood vessels in the body, to produce a vasodilatation effect, which henceforth acts as an anti-platelet.

Contraindications of this drug is very minimal, but very important. Primarily, whoever is taking nitrates, should NOT be taking any phospodiesterase type 5 inhibitor, such as Viagra or Cialis. These medication are used for sexual dysfunctions, and relaxes the blood vessels to produce smooth blood flow into the penis. With nitrates, this will cause severe hypotension, and patient can collapse, or go into a hypotensive shock. This is very important, and must be approached very cautiously. Another important contraindication of this drug, is if the patient is allergic to this medication, or any nitrates as a matter of fact. Having an allergy to a drug in general can be fatal, and is acquired as an emergency situation. Also, if a patient is suspecting a heart attack, or having increased pressure in the brain, or the patient is severly anemic; all these conditions are very fatal if nitrates is taken during this time.

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Moreover, side effects of this drug, again is very similar; possible side effects are burning in the mouth, any form of dizzines, flushines, headache, lightheadedness, hyperhydrosis, nausea and vomiting. It is important to be very aware of your state of body while taking this drug. Any severe side effects such as rash, irritation, difficulty breathing, chest tightness, fainting, blurred vision, slow heartbeat , can all cause a deadly outcome. It is very important to keep updates with your doctor and be sure of everything that happens to your body.

Finally, using nitrates is very common around the globe and is very successful in treating many conditions. Because nitrates widens your blood vessels, it decreases blood pressure. This is good for anyone who has hypertension, heart failure, any heart disease, kidney failure. Nitrates decrease the preload and afterload to the heart, which saves the heart from any attacks, or strokes. Also nitrates is very useful in decreasing oxygen needs of the heart due to less work, which therefore decreases any chest pain.

Glycoprotein IIb/IIIa receptor blockers

An example drug of this certain class, is Aggrastat, which is used as an anti-platelet. It is also called Tirofiban.


This medication, tirofiban, works by inhibiting platelet aggregation. This is done due to its antagonist effect of the platelet glycoprotein IIb/IIIa receptor. This receptor causes aggregation of blood - leading to blood clotting. When we inhibit this receptor, it simultaneously inhibits any platelet aggregation, and therefore saves the patient from any type of disease that comes from blood clotting.

Contraindications of this drug is very important to understand as this drug can cause alot of negative results. If a patient has had a history of stroke, surgery, any trauma, or excessive bleeding, it is a major concern that this patient should not take this medication. If a patient has an aneurysm, any clotting condition, artery/vein disease, or even a tumor to the brain, another drug of choice should be given. High blood pressure, heart inflammation, tear in the aorta, are all major contraindications that should be of concern while taking this drug.

Side effects of this drug is like any other anti-platelet. It is very essential to be careful while taking an medication, and as well any medication that works on the blood or the heart. It is crucial to be careful in these medications. Side effects that can occur are dizziness, headache, sweating, pain in the pelvic area, nausea, and awkward pain in the leg. If severe side effects such as - fainting, severe bleeding, haemorrhage, irritation, skin rash, allergic reactions, difficulty breathing, chest tightness - arise, a medical doctor should be alerted as soon as possible to stop the drug and treat any severe symptoms there are.

Tirofiban is used to treat any unstable angina or certain versions of heart attacks, whether severe or mild. If heparin is being taken by the patient, tirofiban is a good combination to take with. Tirofiban is used as a platelet aggregation inhibitor and therefore decreases the chance of any blood vessel constriction leading to heart problems.

Prostacyclin (PGI2) analogues

An example of a prostacyclin analogue is a drug called Iloprost - generic name is Ventavis.


Iloprost is a drug classified under PGI2 analogues. Iloprost is a synthetic analogue of prostacyclin PGI2. Iloprost dilates systemic and pulmonary arterial vascular beds. It also affects platelet aggregation but the relevance of this effect to the treatment of pulmonary hypertension is unknown. The two diastereo isomers of iloprost differ in their potency in dilating blood vessels, with the 4S isomer substantially more potent than the 4R isomer.

The contraindications for this drug are very minimal. Patients who have had a history of allergy to this drug should not take this medication. It is essential that the patient consults the doctor to make sure that this drug is ok for him/her. Another contraindication is if the patient has a lung problem, or history of lung issues such as chronic respiratory acidosis. Other then these two contraindications, this drug is safe and works properly. Again, consulting the doctor is essential for every move you make.

Side effects of this drug is like any other drug with a few different ones. Things such as back pain, headache, increased cough, jaw tightness, trouble sleeping, tongue pain, muscle cramps, are all possible side effects from this drug. These side effects can be overcome by rest, and any pain killers to soothe the pain. Severe side effects such as, allergic reactions, trouble breathing, chest pounding, irregular heartbeat, flu-like symptoms, wheezing, unusual sweating, should be let known to the doctor to keep track and diagnose any difference in your body with this drug.

Iloprost is a medication that is an anti-platelet agent which reduces hypertension. Iloprost specifically treats high blood pressure in the pulmonary arteries of the lungs in patients with pulmonary arterial hypertension (PAH). This drug is structurally similar to a chemical in our body, called prostacyclin, which naturally dilates our blood vessels; so dilating the blood vessels will result in reducing blood pressure.