CV Clopidogrel Flashcards

1
Q

Clopidogrel

Clinical pharmacology

Common indications

A

Clopidogrel is generally prescribed with aspirin, although clopidogrel may be used alone where aspirin is contraindicated or not tolerated.

  • For treatment of acute coronary syndrome (ACS), where rapid inhibition of platelet aggregation can prevent or limit arterial thrombosis and reduce subsequent mortality.
  • To prevent occlusion of coronary artery stents.
  • For long-term secondary prevention of thrombotic arterial events in patients with cardiovascular, cerebrovascular and peripheral arterial disease.
  • To reduce the risk of intracardiac thrombus and embolic stroke in atrial fibrillation where warfarin and novel oral anticoagulants are contraindicated.
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2
Q

Mechanisms of action?

Thrombotic events occur when platelet-rich thrombus forms in atheromatous arteries and occludes the circulation

A
  • Clopidogrel prevents platelet aggregation and reduces the risk of arterial occlusion by binding irreversibly to adenosine diphosphate (ADP) receptors (P2Y12 subtype) on the surface of platelets.
  • As this process is independent of the cyclooxygenase pathway, its actions are synergistic with those of aspirin.
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3
Q

Important adverse effects?

A
  • The most common adverse effect of clopidogrel is bleeding, which can be serious, particularly if gastrointestinal, intracranial or following a surgical procedure.
  • Gastrointestinal upset, including dyspepsia, abdominal pain and diarrhoea, is also common.
  • As with other antiplatelet agents, clopidogrel can rarely affect platelet numbers as well as function, causing thrombocytopenia
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4
Q

Warnings?

A
  • Clopidogrel is a pro-drug that requires metabolism by hepatic cytochrome P450 enzymes to its active form to have antiplatelet effect.
  • Its efficacy may be reduced by cytochrome P450 inhibitors by inhibiting its activation.
  • Relevant examples: include omeprazole, ciprofloxacin, erythromycin, some antifungals and some SSRIs
  • Where gastroprotection with a proton pump inhibitor (see Aspirin) is required for patients taking clopidogrel, lansoprazole or pantoprazole are preferred over omeprazole as they are considered less likely to inhibit clopidogrel activation.
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5
Q

Practical prescribing

Prescription

A
  • Clopidogrel is only available as an oral preparation. Low doses of clopidogrel require up to a week to reach their full antiplatelet effect.
  • When rapid effect is needed you should prescribe a loading dose,normally 300 mg orally for ACS, in the once-only section of the drug chart before commencing a regular maintenance dose of 75 mg orally daily.
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6
Q

Clinical tip?

A

Clopidogrel acts irreversibly:

  • It therefore takes the lifespan of a platelet (around 7 to 10 days) for its antiplatelet effect to wear off. Clopidogrel should be stopped 7 days before elective surgery or other invasive procedures, unless the risk of stopping clopidogrel exceeds the risk of continuing.
  • Thus in patients who have had a drug-eluting coronary artery stent inserted within the last 12 months, surgery should be delayed if possible.
  • In emergency cases, patients taking clopidogrel may require platelet infusion to help stop bleeding.
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