14. Anti-Platelet Drugs Flashcards
Give the development of a platelet
CD34+ stem cell
Megakaryoblast
Promegakaryocyte
Megakaryocyte
What are the mediators which cause the fragmentation of megakaryocytes to platelets?
Thrombopoietin
IL-3, 6
What are the 2 types of granules present in platelets?
Alpha and dense
What substances are present in alpha granules?
von Willebrand Factor
Fibrinogen
Factor 5
Platelet factor 4
What substances are present in dense granules?
ADP
Ca++
Serotonin
What is the life span of a platelet?
10 days
What is primary haemostasis?
Formation of a platelet plug
What is secondary haemostasis?
Clotting cascade
Fibrin traps RBCs
What is the difference between an arterial and venous clot?
Arterial due to endothelial damage or rupture of atheroma and venous due to stasis near valves
Arterial more platelet rich and venous more fibrin rich
What are the surface glycoprotein receptors on platelets?
GP VI
GPIb-IX-V complex
GPIIIb-IIa complex
What does GP VI bind to?
Collagen
What does the GPIb-IX-V complex bind to?
von Willebrand factor
What does the GPIIb-IIIa complex bind to?
Other platelets
What GPCRs are found on the surface of platelets?
PARs
ADP receptors
Name 2 ADP receptors found on the surface of platelets?
P2Y1
P2Y12
Why is GPIb-IX-V particularly important in high blood pressure?
Holds platelets still at endothelium in fast rushing blood
What integrin works alongside GPVI to allow stable adhesion to collagen?
a2B1
What happens when platelets release dense granules?
Platelet activation and aggregation
How do platelets change shape?
Reorder of actin and tubulin polymers
What method of signalling does thromboxane use?
Autocrine
What happens when ADP binds to P2Y12, 1?
Induce thromboxane synthesis
Activation of GPIIb/IIIa
What kind of signalling is done by GPIIb/IIIa?
Inside out signalling
What enzyme converts prostaglandin to thromboxane A2?
Thromboxane synthase
What cells produce prostacyclin?
Endothelial cells
What are the actions of prostacyclin?
Inhibit platelets
Promote vasodilation
What are the functions of thromboxane?
Activation of platelets
Change shape
Release granules
Aggregation
What are the pathways of platelet activation?
ADP-P2Y12 (thrombin production)
COX-1 (thromboxane production)
PAR-1 (thrombin receptor)
What is the MOA of aspirin?
Irreversibly inhibits COX-1 producing thromboxane
Reduced capacity of platelets to aggregate
What are the uses of aspirin?
Prophylaxis for thrombosis in MI, TIA
Prevent ischaemic events in unstable angina
What drug is aspirin usually used with?
Clopidogrel
What are the contraindications to using aspirin?
Allergy to ibuprofen
Asthma (increase in leucotrienes)
Kidney disease, peptic ulcers, gout, gastritis
Bleeding risks
What is the MOA of dipyridamole?
Reduce uptake of adenosine causing vasodilation
What are the uses of dipyridamole?
With warfarin/ aspirin for stroke/TIA
What are the uses of ADP receptor antagonists?
Secondary prevention of stroke, TIA, MI
Unstable angina
PCI, CABG
Name 3 ADP receptor antagonists
Clopidogrel
Prasugrel
Ticagrelor
Which enzyme metabolises clopidogrel and prasugrel?
CYP2C19
What is the difference between ADP receptor antagonists?
Clopidogrel has a 2 step oxidation process
Prasugrel has a 1 step oxidation and is broken down faster
Ticagrelor is metabolically active
What does clopidogrel bind to?
Cysteine sulphydryl on P2Y12
What are the contraindications for prasugrel?
Stroke/TIA because of high risk of bleeding
What is the half life of ticagrelor?
7 hours: requires BD dosing
Why is there a resistance problem with some ADP receptor inhibitors and how can it be overcome?
Use of the CYP450 enzyme
Using ticagrelor because it’s metabolically active
Name 3 GPIIb/IIIa inhibitors
Abciximab
Tirofiban
Eptifibatide
What is the composition of abciximab?
7E3 Fab fragments
What is the MOA of abciximab?
Binds to RGD site on GPIIb/IIIa
Prevents interaction with fibrinogen
What route are GPIIb/IIIa inhibitors given through?
IV
What are the uses of abciximab?
Unstable angina
PCI
What is the MOA of tirofiban and eptifibatide?
Mimics RGD segment of fibrinogen
What is the use of tirofiban?
PCI
What are the uses of eptifibatide?
Angina or MI
What are the side effects of eptifibatide?
Hypotension
CV failure
Arrhythmias