Platelet Pharmacology Quiz

Question 1

A 55-year-old pharmacology professor is brought to the emergency department 2 h after the onset of severe chest pain during a stressful question and answer session. He has a history of poorly controlled mild hypertension and elevated blood cholesterol but does not smoke. ECG changes (ST elevation) and cardiac enzymes confirm the diagnosis of myocardial infarction. The decision is made to attempt to open his occluded artery.

If this patient undergoes a percutaneous coronary angiography procedure and placement of a stent in a coronary blood vessel, he will need to be on dual antiplatelet therapy, for example aspirin and clopidogrel for at least a year. Which response most accurately describes the mechanism of action of clopidogrel?

Read all of the responses carefully before selecting the best answer!!

A) Clopidogrel directly binds to the platelet ADP receptors
B) Clopidogrel irreversibly inhibit cyclooxygenase
C) Clopidogrel facilitates the action of antithrombin III
D) The active metabolite of clopidogrel binds to and inhibits the platelet ADP receptors

Answer 1

D - Clopidogrel is a prodrug that is activated by CYP2C9 and CYP2C19. It irreversibly binds to the ADP receptor on the surface of platelets that serves as key role in platelet aggregation. Aspirin and clopidogrel help prevent platelet-induced occlusion of coronary stents.

Question 2

A 64 year old woman presents with pain in her left thigh muscle. Duplex US indicates the presence of DVT in the affected limb.

The decision was made to treat this woman with enoxaparin. Relative to unfractionated heparin, enoxaparin:

A) Can be used without monitoring the patient’s aPTT
B) Is more likely to cause thrombosis and TCP
C) Has a shorter duration of action
D) Is less likely to have a teratogenic effect

Answer 2

A - enoxaparin is a LMWH. LMWHs have a longer half life than standard (high molecular weight) heparin and a more consistent relationship between dose and therapeutic effect. Enoxaparin is given subQ, not IV. It is LESS, not MORE, likely to cause thrombosis and TCP. Neither LMWH nor standard heparin are teratogenic. The aPTT is not useful for monitoring the effects of LMWHs.

Question 3

A patient develops severe TCP in response to treatment with unfractionated heparin and still requires parenteral anticoagulation. Your best option is:

A) Eptifibitide
B) Bivalirudin
C) Abciximab
D) Clopidogrel

Answer 3

B - direct thrombin inhibitors such as bivalirudin and argatroban provide parenteral anticoagulation similar to that achieved with heparin, but the direct thrombin inhibitors do not induce formation of antiplatelet antibodies.

Question 4

Match the medication with the most accurate description of its MOA:

Clopidogrel
Aspirin
Heparin and LMWH
Eptifibatide

Prevents binding of fibrinogen and vWF to the GPIIb/IIIa receptor
Activates antithrombin
An active metabolite binds to and inhibits the platelet ADP receptors
Inhibits prostaglandin and thromboxane synthesis

Answer 4

Clopidogrel: An active metabolite binds to and inhibits the platelet ADP receptors
Aspirin: Inhibits prostaglandin and thromboxane synthesis
Heparin and LMWH: Activates antithrombin
Eptifibatide: Prevents binding of fibrinogen and vWF to the GPIIb/IIIa receptor