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Antiplatelets

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Antiplatelets

Key Points

  • Antiplatelet agents decrease platelet activation and aggregation; primary use is prevention and treatment of cardiovascular thromboembolic events.
  • Aspirin inhibits COX-mediated thromboxane A2 production; P2Y12 inhibitors (clopidogrel, ticagrelor, prasugrel) block ADP receptor on platelets.
  • Bleeding is the primary adverse effect across all antiplatelet classes; discontinue 5–7 days before surgery.
  • Clopidogrel is a prodrug requiring CYP2C19 activation; genetic polymorphisms can cause therapeutic failure.

Pathophysiology

Platelets adhere to injured vessel walls and aggregate to form the primary hemostatic plug. Platelet activation is mediated by ADP receptor (P2Y12), thromboxane A2, and GPIIb/IIIa receptors. Antiplatelet drugs block one or more of these pathways, reducing clot formation.

Common indications include: acute coronary syndrome (ACS), post-coronary stent placement, stroke prevention, peripheral arterial disease, and atrial fibrillation (with certain anticoagulants).

Classification

SubclassExamplesMechanism
COX inhibitorAspirinIrreversibly inhibits COX → reduces thromboxane A2
P2Y12 inhibitorsClopidogrel, ticagrelor, prasugrel, cangrelorBlock ADP receptor → prevent platelet aggregation
GPIIb/IIIa inhibitorsAbciximab, eptifibatide, tirofibanBlock fibrinogen receptor → most potent; IV use in ACS
PDE inhibitorsDipyridamole, cilostazolIncrease cAMP → inhibit platelet aggregation

Nursing Assessment

NCLEX Focus

Monitor for bleeding; hold P2Y12 inhibitors 5–7 days before surgery; verify CYP2C19 status with clopidogrel use.

  • Assess baseline CBC, PT/INR, aPTT, and platelet count before initiating therapy.
  • Assess for concurrent anticoagulant, NSAID, or herbal supplement use (ginkgo, garlic, fish oil) — increased bleeding risk.
  • Assess renal/hepatic function; prasugrel is contraindicated in prior stroke/TIA and in patients <60 kg or ≥75 years.
  • Assess for perioperative timing: most antiplatelets should be held 5–7 days pre-surgery per surgical team.

Nursing Interventions

  • Instruct patients to take aspirin with food to reduce GI adverse effects; enteric-coated formulations may decrease gastric irritation.
  • For acute MI with aspirin indicated: have patient chew aspirin (not swallow whole) for rapid absorption.
  • Teach patients not to take OTC NSAIDs concurrently with aspirin — pharmacodynamic drug interaction increases bleeding risk.
  • Monitor for signs of bleeding: petechiae, bruising, blood in stool/urine, prolonged bleeding from minor cuts.

Perioperative Antiplatelet Management

Discontinue clopidogrel, ticagrelor, prasugrel 5–7 days before elective surgery to reduce surgical bleeding risk. Never discontinue antiplatelet therapy in patients with recent coronary stent without provider guidance — stent thrombosis can be fatal.

Aspirin in Pediatrics

Aspirin is contraindicated in children with viral illnesses due to Reye syndrome risk (potentially fatal hepatic failure and encephalopathy).

Pharmacology

DrugRoute/DoseKey Nursing Considerations
Aspirin81–325 mg orally dailyIrreversible COX inhibition; GI risk; avoid in children; chew for acute MI
Clopidogrel (Plavix)75 mg orally dailyProdrug via CYP2C19; genetic polymorphism risk; avoid omeprazole (CYP2C19 inhibitor)
Ticagrelor (Brilinta)90 mg orally twice dailyNot a prodrug; dyspnea common side effect; do not exceed aspirin 100 mg/day with ticagrelor
Prasugrel (Effient)10 mg orally dailyHighest bleeding risk; contraindicated in prior stroke/TIA; not for patients <60 kg

Clinical Judgment Application

Clinical Scenario

A patient taking clopidogrel for a coronary stent is scheduled for elective hip replacement surgery in 5 days.

  • Recognize Cues: Antiplatelet use with upcoming surgery creating bleeding risk vs. stent thrombosis risk.
  • Analyze Cues: 5 days is marginal; stent age determines whether antiplatelet therapy can be safely interrupted.
  • Prioritize Hypotheses: Coordinated surgical/cardiological decision about antiplatelet continuation.
  • Generate Solutions: Notify surgeon and cardiologist; do not discontinue without provider guidance.
  • Take Action: Document stent type and date; facilitate provider communication; delay surgery if stent is <30 days old.
  • Evaluate Outcomes: Surgical plan adjusted with appropriate antiplatelet management documented.
  • anticoagulants - Complementary hemostasis modulation; combination increases bleeding risk.
  • coronary-artery-disease - Primary indication for antiplatelet therapy post-ACS or stent.
  • deep-vein-thrombosis - Anticoagulants preferred over antiplatelets for VTE.
  • anticoagulants - Often used with antiplatelets in acute coronary syndromes.
  • nsaids - Pharmacodynamic interaction increasing GI and systemic bleeding risk.

Self-Check

  1. Why should aspirin be chewed rather than swallowed in acute MI?
  2. What CYP2C19 drug interaction limits clopidogrel effectiveness?
  3. Why is prasugrel contraindicated in patients with prior stroke or TIA?

Graph View

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