A 62-year-old woman with acute PE and hemodynamic instability (systolic BP 85 mmHg, RV dysfunction on echo) is admitted to the ICU. She has no absolute contraindications to thrombolysis. What is the drug of choice for immediate thrombolytic therapy?

Explanation

## Thrombolytic Therapy in Massive (Hemodynamically Unstable) PE **Key Point:** Alteplase (recombinant tissue plasminogen activator, rt-PA) is the FDA-approved and preferred thrombolytic agent for massive PE because it is fibrin-specific, has rapid onset, and has the strongest evidence base in PE management. ### Indications for Thrombolysis in PE Thrombolysis is indicated in: 1. **Massive PE** (hemodynamic instability: SBP <90 mmHg, shock, RV dysfunction) 2. **Submassive PE** with adverse prognostic markers (elevated troponin, BNP, RV strain) in selected cases 3. **Contraindications to anticoagulation** are NOT present ### Thrombolytic Agents: Comparison | Agent | Fibrin-Specificity | Approval in PE | Onset | Dosing in PE | Notes | |-------|-------------------|----------------|-------|--------------|-------| | **Alteplase** | High | FDA-approved | 10–20 min | 100 mg IV over 2 hrs | Gold standard; most evidence | | **Tenecteplase** | Very high | Not FDA-approved for PE | 5–10 min | Weight-based bolus | Used off-label; faster | | **Urokinase** | Non-specific | Withdrawn in US | Slower | Bolus + infusion | Rarely used now | | **Streptokinase** | Non-specific | Not approved for PE | Slower | Bolus + infusion | Antigenic; inferior outcomes | **High-Yield:** Alteplase is preferred because: - **Fibrin-specific**: binds to fibrin in the thrombus, minimizing systemic fibrinolysis and reducing bleeding risk - **Rapid clot lysis**: begins within 10–20 minutes - **Level 1 evidence**: multiple RCTs support its use in massive PE - **FDA-approved**: standardized dosing and safety profile **Clinical Pearl:** Alteplase dosing in PE is **100 mg IV over 2 hours** (NOT the 15 mg bolus + 50 mg over 30 min used in acute MI). This slower infusion reduces intracranial hemorrhage risk. ### Mechanism: Why Fibrin-Specificity Matters ```mermaid flowchart TD A[Thrombolytic Agent]:::action --> B{Fibrin-Specific?}:::decision B -->|Yes: Alteplase| C[Binds fibrin in clot]:::outcome B -->|No: Streptokinase| D[Systemic fibrinolysis]:::outcome C --> E[Targeted clot lysis]:::action D --> F[Widespread bleeding risk]:::urgent E --> G[Lower hemorrhage rate]:::outcome F --> H[Higher hemorrhage rate]:::urgent ``` **Mnemonic: ALTEPLASE ADVANTAGE** — **A**pproved for PE, **L**ow systemic fibrinolysis, **T**issue-specific, **E**vidence-based, **P**erfect dosing (100 mg/2 hrs), **L**ess bleeding, **A**ctive within 10–20 min, **S**tandard of care, **E**ffective in massive PE. ### Contraindications to Thrombolysis - Active bleeding or bleeding disorder - Recent surgery or trauma (<2 weeks) - Intracranial pathology (stroke, tumor, hemorrhage) - Uncontrolled hypertension (SBP >180 mmHg) - Pregnancy (relative) [cite:Harrison 21e Ch 297]