Antiplatelets vs Anticoagulants vs Thrombolytics — Mechanism and Clinical Selection

What is the clinical goal?

• PREVENT a new arterial clot (MI prevention, post-stent, stroke prevention in TIA)?

  • → Antiplatelet agent
  • Drugs: aspirin (81–325 mg), clopidogrel (Plavix), ticagrelor, prasugrel
  • Mechanism: blocks platelet aggregation — platelets can't clump
  • Monitoring: no routine labs; watch for bruising, bleeding gums, black stools
  • Key point: works on ARTERIAL side (high-flow, platelet-rich "white clots")
  • Duration: often lifelong; dual antiplatelet therapy (aspirin + clopidogrel) × 12 months post-stent
  • Do NOT stop abruptly before consulting provider — rebound thrombosis risk

• PREVENT or TREAT a venous clot (DVT, PE, AFib stroke prevention)?

  • → Anticoagulant
  • Drugs: heparin (IV/SubQ), enoxaparin (Lovenox), warfarin (Coumadin), DOACs (rivaroxaban, apixaban)
  • Mechanism: inhibits clotting cascade factors — prevents fibrin formation
  • Does NOT dissolve existing clots — prevents extension while the body lyses them naturally

  Which anticoagulant?

  • Acute inpatient (DVT, PE, bridging)?
    • Heparin IV drip — onset minutes, short half-life, titratable
    • Monitor: aPTT every 6 hours (goal 1.5–2.5× normal)
    • Antidote: protamine sulfate
  • Subacute/outpatient bridge?
    • Enoxaparin SubQ — no routine aPTT; monitor anti-Xa if needed
    • Antidote: protamine (partial reversal)
  • Long-term oral (AFib, mechanical valve, recurrent VTE)?
    • Warfarin — monitor INR (goal 2.0–3.0; mechanical valve 2.5–3.5)
    • Onset: 3–5 days (overlap with heparin until INR therapeutic × 24 hr)
    • Antidote: vitamin K (phytonadione), fresh frozen plasma for emergencies
    • Interactions: vitamin K–rich foods, many drugs (CYP metabolism)
  • Long-term oral (AFib, VTE — NOT mechanical valves)?
    • DOAC (rivaroxaban, apixaban) — no routine lab monitoring
    • Antidote: andexanet alfa (for factor Xa inhibitors), idarucizumab (dabigatran)

• DISSOLVE an existing acute clot causing organ damage RIGHT NOW?

  • → Thrombolytic (fibrinolytic)
  • Drug: alteplase (tPA) — most commonly tested
  • Mechanism: converts plasminogen → plasmin → breaks down fibrin clot
  • Indications: acute STEMI (within 12 hr), acute ischemic stroke (within 4.5 hr), massive PE with hemodynamic instability

  Time windows are non-negotiable:

  • Ischemic stroke: ≤ 4.5 hours from symptom onset (fewer exclusion criteria if ≤ 3 hr)
  • STEMI: ≤ 12 hours from symptom onset (door-to-needle ≤ 30 min if no PCI available)
  • Must confirm NO hemorrhagic stroke via CT before giving alteplase

  Absolute contraindications (memorize these):

  • Active internal bleeding or hemorrhagic stroke
  • Recent (2–3 months) intracranial surgery or head trauma
  • Known intracranial neoplasm or AVM
  • Severe uncontrolled hypertension (> 185/110 for stroke)
  • Recent major surgery (within 14–21 days)

  Nursing priorities during thrombolytic infusion:

  • Neuro checks every 15 minutes (stroke) — any decline → stop infusion, stat CT
  • No IM injections, no arterial punctures, no invasive procedures
  • Monitor all puncture sites for oozing
  • Keep aminocaproic acid (Amicar) at bedside — antidote for fibrinolytic bleeding
  • No anticoagulants or antiplatelets during infusion

Bleeding risk escalation (this is what the NCLEX tests):

• Antiplatelet = lowest bleeding risk → used for chronic prevention
• Anticoagulant = moderate bleeding risk → used for prevention and treatment
• Thrombolytic = highest bleeding risk → reserved for life-threatening emergencies with strict time windows