Anti-Platelet Drugs

Question 1

what are anti-platelets used for

Answer 1

arterial atherosclerotic events

Question 2

what causes arterial thrombosis

Answer 2

high pressure system

atherosclerosis (formation of cholesterol plaque which rupture and exposes collagen. platelets attracted to collagen forming a plug around the plaque blocking the lumen of the vessel)

platelet rich thrombus

Question 3

treatment of arterial thrombosis

Answer 3

aspirin and other anti-platelets

modify risk factors

Question 4

what is atherosclerosis

Answer 4

damage to endothelium

recruitment of ‘foamy’ macrophages rich in cholesterol

forms cholesterol plaque

Question 5

what does a stable atherosclerotic plaque cause

Answer 5

stable angina

intermittent claudication

(stable is hyalinised and calcified)

Question 6

what do unstable atherosclerotic plaques cause

Answer 6

unable angina
MI
Stroke

Question 7

what is unstable angina

Answer 7

plaque ruptures

platelets are recruited and cause an acute thrombus to form

this occludes the vessel

Question 8

what is the role of platelets in atherosclerosis

Answer 8

plaques only form in high pressure environments

plaque ruptures due to the high pressure

platelets then adhere to the plaque as it exposes damaged epithelium

platelets become activated and release granules that activate coagulation and recruit other platelets to form platelet plug

platelets aggregate via membrane glycoproteins

this forms an acute thrombosis - vessel occlusion

Question 9

risk factors for arterial thrombosis

Answer 9

hypertension

• damage to endothelium
• platelet activation

smoking

• endothelial damage (toxins directly damage and also increase BP causing damage)
• platelet activation

high cholesterol
-accumulated in plaques

diabetes mellitus

• endothelium damage (from high glucose)
• platelet activation
• more cholesterol

Question 10

prevention of arterial thrombosis

Answer 10

stop smoking 
treat hypertension 
treat diabetes 
lower cholesterol 
anti-platelet drugs

Question 11

how are platelets formed

Answer 11

in the bone marrow by ‘budding’ off from the megakaryocytes

Question 12

structure of platelets

Answer 12

small enucleate discs with a mean lifespan of 7-10 days

Question 13

what chemicals are secreted by platelets to increase aggregation

Answer 13

thromboxane A2

ADP

Question 14

what allows platelets to attach to each other

Answer 14

glycoproteins

fibrinogen

Question 15

how does aspirin work as an anti-platelet

Answer 15

inhibits cyclo-oxygenase which is necessary to produce thromboxane A2 (a platelet agonist released from granules on activation

Question 16

side effects of aspirin

Answer 16

bleeding

blocks production of prostaglandins leading to:

• GI ulceration
• Bronchospasm

Question 17

what does cyclo-oxygenase do

Answer 17

converts arachidonic acid to prostaglandins

thromboxane synthase then converts prostaglandins to thromboxane

Question 18

what is clopidogrel

Answer 18

ADP receptor antagonist

Question 19

what is dipyridamole

Answer 19

phosphodiesterase inhibitor

-reduced the production of cAMP which is a ‘second messenger’ in platelet activation

Question 20

what are GP IIb/IIIa inhibitors

Answer 20

antiplatlet drug

v potent

only given at high risk time then switched off again

Question 21

side effects of anti-platelet drugs

Answer 21

bleeding
(drugs effect platelet’s entire lifespan 7-10 days)

stop anti-platelet agents 7 days proper to elective operations

if serious bleeding reverse with platelet transfusion