tPA
Meaning of tPA: The body's own clot dissolving switch, borrowed as a drug because it works hardest exactly where a clot has formed.
Definition of tPA
tPA stands for tissue plasminogen activator, an enzyme released by the cells lining blood vessels that starts the breakdown of a clot. It converts plasminogen, an inactive protein caught inside the clot, into plasmin, which cuts up the fibrin mesh holding the clot together. Manufactured versions are given as emergency treatment for stroke, heart attack and clots in the lung.
How does it dissolve a clot?
A clot is a mesh of fibrin threads with blood cells trapped in it. The body keeps a dismantling system on standby, and tPA is its trigger. This enzyme converts plasminogen into plasmin, and plasmin chops the fibrin mesh into fragments that dissolve away. The elegance is in the targeting: tPA works far more efficiently once bound to fibrin, so it is most active on the surface of a clot and much less so in freely flowing blood. That built in preference limits, without removing, the effect on clotting elsewhere.
Where is the manufactured form used?
| Condition | What the drug does |
|---|---|
| Ischemic stroke | Reopens a blocked brain artery within a narrow window after symptoms begin |
| Heart attack | Restores flow where opening the artery mechanically is not quickly available |
| Pulmonary embolism | Breaks up a large clot in the lung that is collapsing the circulation |
| Blocked catheter | A small dose clears a clot inside the line |
Recombinant tissue plasminogen activator is the manufactured version, grown in cultured cells rather than extracted from human tissue. Alteplase and tenecteplase are the forms in common use, the second altered so it lasts longer and can be given as a single push.
Why is timing so critical?
Tissue starved of blood dies progressively, and restoring flow helps only while cells remain salvageable. Once tissue has died, opening the vessel cannot recover it and raises the chance of bleeding into the damaged area. The window is therefore counted from when symptoms began rather than from when help was sought, and an unknown time of onset changes the assessment entirely. That reasoning is what drives the urgency of stroke pathways.
What is the main risk?
Bleeding, since a drug that dissolves harmful clots also dissolves protective ones. Bleeding into the brain is the most feared complication, and it is the reason a scan comes first, to confirm that a stroke is caused by a blockage rather than by a hemorrhage. Recent surgery, active bleeding, a history of bleeding in the brain and very high blood pressure all weigh against its use, and the decision sets a defined chance of harm against a larger chance of benefit.
Also known as
Used in a sentence
Intravenous tPA was given after imaging excluded hemorrhage.
Good to know
Clot dissolving treatment cannot tell a harmful clot from a protective one, so bleeding is its principal risk, and imaging is done first to confirm that a stroke is caused by a blockage rather than by bleeding.