Thrombolytics
High-yield Verified · Oct 2026Thrombolytics put the body’s own fibrinolytic system to work, turning fibrin-bound plasminogen into plasmin so the clot is digested from within. Everything else follows from where that plasmin acts and how long the activator survives in plasma.
Nursing view → administration, monitoring and patient teaching
Compare: Antithrombotics compared — anticoagulants, antiplatelets and thrombolytics →
Drugs
Mechanism
Alteplase and tenecteplase are recombinant tissue plasminogen activators (serine proteases). They bind fibrin in a thrombus and convert the entrapped plasminogen to plasmin, which degrades fibrin and dissolves the clot. Conversion is enhanced in the presence of fibrin, limiting systemic plasminogen activation. Tenecteplase is a modified tPA with higher fibrin specificity, greater resistance to plasminogen activator inhibitor-1 (PAI-1) and a longer half-life than native tPA, so it is given as a single bolus.
The fibrinolytic system and its brakes
Fibrinolysis is the body’s counterweight to clotting. Thrombin stimulates endothelial cells to release tissue plasminogen activator (tPA); tPA and plasminogen assemble on fibrin, binding to lysine sites on the clot, and tPA there converts plasminogen into its active form, plasmin. Plasmin acts directly on the fibrin mesh and breaks it down. Plasmin can also be generated in other ways, such as by urokinase and kallikrein.
The system has brakes: fibrinolysis is inhibited by plasminogen activator inhibitors 1 and 2 (PAI-1, PAI-2) and by thrombin bound to thrombomodulin, which activates thrombin-activatable fibrinolysis inhibitor. Alteplase is recombinant tPA itself; tenecteplase is a version engineered to resist PAI-1.
Fibrin specificity and the TNK redesign
Alteplase is a serine protease whose conversion of plasminogen is fibrin-enhanced: it produces limited conversion in the absence of fibrin. Bound to fibrin in a thrombus, it converts the entrapped plasminogen and starts local fibrinolysis with limited systemic proteolysis. Kinetically, it is cleared from plasma with an initial half-life of less than 5 minutes, so it must be infused.
Tenecteplase is a 527-amino-acid tPA variant with three changes — threonine 103 to asparagine and asparagine 117 to glutamine (both in the kringle 1 domain), and a tetra-alanine substitution at positions 296–299 in the protease domain; the letters T, N and K stand for the three regions changed. The result is much higher fibrin specificity, increased resistance to inactivation by PAI-1, and a longer half-life than native tPA — long enough for a single IV bolus. The label adds that the clinical significance of the greater fibrin specificity for bleeding or efficacy has not been established.
Why they bleed — and what opposes plasmin
Fibrin specificity is relative. Plasmin lyses fibrinogen as well as fibrin, and circulating fibrinogen falls after treatment — by 16–36% after 100 mg of alteplase, with 11% of patients in one trial dropping below 100 mg/dL — and by 4–15% after tenecteplase, with plasminogen falling 11–24%. The drugs stay active in a blood sample, so coagulation and fibrinolysis tests drawn during therapy can be falsely abnormal: fibrinogen keeps being degraded in the tube.
Intracranial hemorrhage is the bleed that matters most. In the alteplase stroke trials, age over 77 and severe deficit (NIHSS > 22) were among the baseline features linked to more intracranial hemorrhage, and doses above the labelled stroke dose may raise its incidence. There is no antidote; instead the countermeasures replace what plasmin consumes or block plasminogen. Cryoprecipitate is commonly used to restore fibrinogen after symptomatic intracranial hemorrhage, with antifibrinolytic therapy considered when cryoprecipitate is delayed or unavailable. Tranexamic acid and aminocaproic acid are lysine analogs that bind plasminogen’s lysine sites, so it cannot bind fibrin and be converted to plasmin.
Angioedema: a bradykinin effect
Angioedema after thrombolysis is linked to bradykinin. Plasminogen activation feeds bradykinin synthesis — which is why tranexamic acid, by interrupting plasminogen activation, can limit bradykinin production. ACE inhibitors add to this from the other side: ACE-inhibitor angioedema reflects decreased bradykinin degradation (the kinin pathway is on the ACE inhibitor page). Bradykinin causes vasodilation and plasma leakage into tissue, so the face, lips and airway swell.
That explains the alteplase label’s observation that many patients with angioedema were taking an ACE inhibitor, and why bradykinin-directed therapy is part of managing airway-threatening orolingual angioedema; patients with alteplase-associated orolingual angioedema have responded rapidly to icatibant, a bradykinin-receptor antagonist.
Comparing the drugs
Alteplase versus tenecteplase
| Drug | Molecule | Half-life | How given | Fibrinogen fall | Labelled uses |
|---|---|---|---|---|---|
| Alteplase | Recombinant native tPA; fibrin-enhanced | Initial < 5 min; terminal 72 min | IV bolus + infusion; Cathflo: instilled into the catheter | 16–36% (100 mg) | Acute ischemic stroke, AMI, massive PE; blocked central lines (Cathflo) |
| Tenecteplase | tPA with 3 substitutions; higher fibrin specificity, PAI-1-resistant | Terminal 90–130 min | Single IV bolus over 5 seconds, weight-tiered | 4–15% (plasminogen 11–24%) | Acute ischemic stroke, STEMI |
Head to head, tenecteplase matched alteplase: no significant difference in a good stroke outcome (mRS 0–1) in the AcT trial, and a 30-day mortality relative risk of 1.00 versus accelerated alteplase in STEMI (ASSENT-2).
Agents that oppose fibrinolysis
| Drug | What it does | Role after thrombolysis |
|---|---|---|
| Cryoprecipitate | Restores fibrinogen | Commonly used for symptomatic intracranial hemorrhage after alteplase or tenecteplase |
| Tranexamic acid | Synthetic lysine analog; reversible competitive inhibitor of the lysine receptor on plasminogen, so plasmin cannot bind the fibrin matrix | Antifibrinolytic option when cryoprecipitate is delayed or unavailable |
| Aminocaproic acid | Lysine analog that binds plasminogen, preventing its binding to fibrin and conversion to plasmin; also inhibits plasminogen activators and, less, plasmin | Antifibrinolytic for bleeding from excess fibrinolytic activity |
Pharmacokinetics
- Alteplase — distribution and clearance — alteplase
- Rapidly cleared, initial half-life under 5 minutes (terminal about 72 minutes); plasma clearance 380–570 mL/min, mainly by the liver; initial volume of distribution about plasma volume.
- Tenecteplase — distribution — tenecteplase
- Biphasic disposition after a bolus. The central volume of distribution (4.2–5.4 L) approximates plasma volume; the steady-state volume is about 50% larger, suggesting some extravascular distribution.
- Tenecteplase — elimination — tenecteplase
- Terminal half-life 90–130 minutes; linear kinetics, with clearance of about 99–119 mL/min across the 30–50 mg doses; liver metabolism is the major clearance mechanism.
- Body weight — tenecteplase
- Total body weight explained 19% of the variability in tenecteplase clearance and 11% of volume of distribution; a weight-adjusted dose gave a better patency-to-bleeding relationship than fixed doses, the framework for the weight-tiered regimen.
- Pharmacodynamic footprint
- Circulating fibrinogen falls 16–36% after 100 mg of alteplase and 4–15% after tenecteplase, which also lowers plasminogen 11–24% — the measurable cost of incomplete fibrin specificity.
- Catheter instillation — alteplase (Cathflo Activase)
- Instilled into a central venous access device, alteplase is not expected to reach pharmacologic plasma levels; even 2 mg given straight into the circulation would return to endogenous levels (5–10 ng/mL) within 30 minutes.
- In vitro activity
- Both enzymes remain active in a blood sample, degrading its fibrinogen, so coagulation and fibrinolysis tests during therapy may be unreliable unless specific precautions are taken.
Uses & drug choice
- Acute ischemic stroke — started within 3 hours of symptom onset, after intracranial hemorrhage is excluded
- Acute myocardial infarction — to reduce mortality (tenecteplase in ST-elevation MI; alteplase also to reduce heart failure)
- Alteplase for acute massive pulmonary embolism (lysis of emboli obstructing a lobe or multiple lung segments)
- Alteplase (Cathflo Activase) for occluded central venous access devices — restores the ability to withdraw blood
Adverse effects
- Bleeding at puncture sites, GI and GU tracts
- Plasmin lyses fibrin and fibrinogen; fibrin specificity limits but does not prevent systemic fibrinogen loss, and other drugs that impair hemostasis add to the risk.
- Intracranial hemorrhage
- Age over 77 and severe deficit (NIHSS > 22) were linked to more intracranial hemorrhage in the alteplase stroke trials, and doses above the labelled stroke dose may raise its incidence.
- Angioedema
- Bradykinin-mediated: plasminogen activation drives bradykinin synthesis, and ACE inhibitors slow bradykinin degradation; bradykinin causes vasodilation and plasma extravasation.
- Thromboembolism and re-embolization
- Lysis can free fragments of an existing clot — a left heart thrombus in mitral stenosis or atrial fibrillation, or deep venous thrombi in PE, which alteplase does not adequately treat.
- Cholesterol embolization
- Rare and of uncertain incidence; associated with invasive vascular procedures and anticoagulant therapy, presenting with livedo reticularis, “purple toe” syndrome or acute renal failure.
- Arrhythmias after coronary lysis
- They are arrhythmias associated with reperfusion after coronary thrombolysis — sinus bradycardia, accelerated idioventricular rhythm, premature ventricular beats or VT.
Toxicity & antidote
Overdose means serious bleeding, and there is no specific antidote: the drug is stopped and supportive care given. For suspected symptomatic intracranial hemorrhage, any running infusion is stopped and emergent CT, blood count, PT/INR, aPTT, fibrinogen and a type and crossmatch are obtained.
Reversal targets the lytic state: cryoprecipitate restores fibrinogen, and an antifibrinolytic (tranexamic acid or aminocaproic acid, lysine analogs that block plasminogen binding to fibrin) is considered when cryoprecipitate is delayed or unavailable.
Interactions
Contraindications
- Active internal bleeding — Thrombolytics can cause significant, sometimes fatal, bleeding; with active bleeding the risk is greater than any benefit.
- Current intracranial or subarachnoid hemorrhage (stroke treatment) — Intracranial hemorrhage must be excluded as the cause of stroke symptoms before treatment — hemorrhagic stroke is a contraindication.
- Recent intracranial or intraspinal surgery or serious head trauma (alteplase: within 3 months; tenecteplase: within 2 months) — Listed as a situation in which the risk of bleeding is greater than the potential benefit.
- Intracranial conditions that increase bleeding risk — intracranial neoplasm, arteriovenous malformation or aneurysm — The labels list these as intracranial conditions that may increase the risk of bleeding.
- Bleeding diathesis — Hemostatic defects add to the bleeding risk of thrombolytic therapy.
- Current severe uncontrolled hypertension — Hypertension above 175/110 mm Hg already raises bleeding risk; severe uncontrolled hypertension is an outright contraindication.
- MI or PE treatment: history of recent stroke (alteplase); any history of intracranial hemorrhage, or ischemic stroke within 3 months (tenecteplase) — Labeled contraindications for treating MI or PE — situations in which the risk of bleeding is greater than the potential benefit.
- Cathflo Activase: known hypersensitivity to alteplase or any component — Hypersensitivity, including urticaria, angioedema and anaphylaxis, has been reported with Cathflo Activase.
- Higher bleeding risk — recent major surgery, GI or GU bleeding or trauma; BP above 175/110 mm Hg; acute pericarditis; subacute bacterial endocarditis; severe liver or kidney disease; pregnancy; diabetic hemorrhagic retinopathy; advanced age; current anticoagulants use caution — Not absolute, but each label says the increased bleeding risk in these conditions must be weighed against the expected benefit.
- Likely left heart thrombus (e.g., mitral stenosis, atrial fibrillation) use caution — Thrombolytics can increase the risk of thromboembolic events when a left heart thrombus is likely.
- Cathflo Activase: known or suspected catheter infection use caution — Treating an infected catheter may release a localized infection into the bloodstream; sepsis occurred in trials.
High-yield
- Tougher — resists inactivation by PAI-1
- Nimbler — higher fibrin specificity than native tPA
- Keeps going — longer half-life (terminal 90–130 min), so one IV bolus
- The letters themselves mark the three regions changed from native tPA
- Refill — cryoprecipitate restores the fibrinogen plasmin consumed
- Lock — tranexamic acid or aminocaproic acid locks plasminogen’s lysine sites so it cannot bind fibrin
- Lock is considered when Refill is delayed or unavailable; there is no specific antidote
Practice questions
Q1A 67-year-old woman with hypertension treated with lisinopril receives IV alteplase for an acute ischemic stroke. Forty minutes into the infusion her tongue and lips swell; there is no urticaria or wheeze.
Which mediator best explains this reaction?
- A.Bradykinin, generated with plasminogen activation and degraded more slowly with ACE inhibition
- B.Leukotrienes from COX inhibition
- C.Histamine released by IgE-sensitized mast cells
- D.Thromboxane A₂ from activated platelets
- E.Serotonin released from platelets
Show answer
A. Bradykinin, generated with plasminogen activation and degraded more slowly with ACE inhibition — Orolingual angioedema with alteplase is linked to bradykinin: plasminogen activation feeds bradykinin synthesis (tranexamic acid limits it by interrupting that activation), and ACE inhibitors reduce bradykinin degradation. Many patients with alteplase angioedema were taking an ACE inhibitor. Bradykinin-mediated angioedema is distinct from histamine-mediated (allergic) angioedema and is not triggered by allergic reactions or hives. Alteplase acts by converting fibrin-bound plasminogen to plasmin; it does not inhibit cyclooxygenase or activate platelets, so leukotrienes, thromboxane A₂ and serotonin are not the link.
Q2Forty-five minutes into an alteplase infusion for stroke, a 74-year-old man becomes drowsy and his deficit worsens. The infusion is stopped and CT shows a new intracerebral hemorrhage. Fibrinogen is markedly low.
Which product most directly restores the factor consumed by the drug?
- A.Vitamin K
- B.Protamine sulfate
- C.Cryoprecipitate
- D.Aminocaproic acid
- E.Idarucizumab
Show answer
C. Cryoprecipitate — Plasmin generated by alteplase lyses fibrinogen as well as fibrin. Cryoprecipitate is commonly used to restore fibrinogen after symptomatic intracranial hemorrhage; an antifibrinolytic such as aminocaproic acid or tranexamic acid blocks further plasminogen activation and is considered when cryoprecipitate is delayed or unavailable, but it does not replace fibrinogen. Vitamin K is the antidote for warfarin, protamine reverses heparin, and idarucizumab reverses dabigatran.
Q3A drug company modifies human tissue plasminogen activator at two sites in kringle 1 and with a tetra-alanine substitution in the protease domain. Unlike the parent molecule, the new drug is given as one 5-second IV injection.
Which property of the new molecule best explains the single-bolus regimen?
- A.It is a prodrug activated in the liver
- B.It binds plasminogen irreversibly
- C.It is excreted unchanged by the kidneys
- D.Its longer plasma half-life
- E.It inhibits plasminogen activator inhibitor-1 synthesis
Show answer
D. Its longer plasma half-life — Tenecteplase has higher fibrin specificity, resistance to inactivation by PAI-1 and a longer half-life than native tPA; because of its long half-life it can be given as a single IV bolus (terminal half-life 90–130 minutes, versus an initial alteplase half-life under 5 minutes). It is not a prodrug — tenecteplase itself binds fibrin and converts plasminogen — and it is cleared mainly by liver metabolism; it resists PAI-1 rather than blocking its synthesis.
Q4During an alteplase infusion for massive pulmonary embolism, a blood sample for coagulation studies is drawn by fresh venipuncture from the opposite arm, away from all infusions. The fibrinogen reported is far lower than expected from the patient’s clinical state and from a sample drawn with appropriate precautions.
What best explains the discrepancy?
- A.Heparin contamination of the sample
- B.Disseminated intravascular coagulation
- C.Hemodilution from the infusion volume
- D.Antibodies against alteplase
- E.Alteplase remained active in the tube and degraded fibrinogen in vitro
Show answer
E. Alteplase remained active in the tube and degraded fibrinogen in vitro — At pharmacologic concentrations alteplase stays active in vitro and can degrade fibrinogen in blood removed for analysis, so coagulation tests and measures of fibrinolytic activity may be unreliable during therapy unless specific precautions are taken to prevent in vitro artifacts.
Sources
- ACTIVASE (alteplase) — FDA label: indications, contraindications, bleeding, angioedema, mechanism, half-life — FDA / DailyMed
- TNKASE (tenecteplase) — FDA label: stroke and STEMI, contraindications, dextrose incompatibility, fibrin specificity — FDA / DailyMed
- CATHFLO ACTIVASE (alteplase) — FDA label: restoring central venous access device function — FDA / DailyMed
- Alteplase — mechanism, monitoring, no antidote — StatPearls (NCBI)
- Tenecteplase — fibrin specificity, PAI-1 resistance, neurologic monitoring — StatPearls (NCBI)
- Open RN Nursing Pharmacology — Ch. 6 §6.12 (blood coagulation modifiers; ISMP high-alert; alteplase grid) — Open RN (NCBI Bookshelf)
- The use of stems in the selection of INN (2018) — -teplase — World Health Organization
- Aminocaproic Acid — fibrinolysis physiology, lysine-analog mechanism — StatPearls (NCBI)
- Tranexamic Acid — lysine-site mechanism — StatPearls (NCBI)
- Acute Stroke: Evaluation and Management — managing intracranial hemorrhage after thrombolysis — StatPearls (NCBI)
- Angioedema — bradykinin-mediated angioedema, icatibant — StatPearls (NCBI)
- ACE Inhibitors — bradykinin and plasminogen activation — StatPearls (NCBI)
- Physiology, Coagulation Pathways — plasmin breaks down fibrin — StatPearls (NCBI)
By LearnDrugs
Educational summary for medical students. Always verify against current prescribing information and guidelines. Not medical advice.