Q. My father recently had an ischemic stroke. He was treated with tPA and has now fully recovered. What is tPA? And how does it work?
A. The most common kind of stroke is called an ischemic stroke: an artery supplying the brain becomes blocked by a blood clot. The part of the brain supplied by the artery needs the nutrition provided by a constant supply of blood. When that supply is interrupted, brain cells can die, taking with them the ability to move, speak, feel or think.
When a stroke occurs, immediate treatment is crucial. The sooner treatment starts, the better the chance of limiting disability or brain damage -- or preventing death.
As soon as doctors diagnose an ischemic stroke, they must determine whether a clot is still blocking an artery. If so, there are drugs to dissolve the clot. Tissue plasminogen activator (tPA) is one of the main drugs used to dissolve clots. It is made naturally by the body, but unfortunately, when a clot suddenly blocks an artery, the body doesn't make enough tPA to dissolve the clot.
However, tPA produced in the form of a medicine can be given through a thin tube in the arm or a tube threaded through the blood vessels directly to the site of the blockage. High concentrations of tPA build up at the site of the clot, making it dissolve. (I've put an illustration of how tPA works to restore blood flow to the brain on my website, AskDoctorK.com.)
Dissolving a clot won't help the brain if it's done too late. The phrase doctors use is, "Time is brain." To be effective, tPA should be administered within 4 1/2 hours after the start of the stroke. When used appropriately, tPA can produce dramatic recovery within hours.
But clot-dissolving drugs also carry risks, and tPA can cause excessive bleeding -- which can lead to death. The more time that passes between the start of the stroke and the administration of tPA, the greater this risk.
Clearly, doctors must exercise great caution when deciding whether to use tPA. When possible, this decision is best made by a skilled medical team headed by a stroke specialist.
If doctors rule out tPA, they will likely give an antithrombotic, or anticoagulant drug, such as heparin, to prevent more clots from forming.
When I was a young physician, there was very little we could do for people with ischemic strokes. We knew what the problem was -- a clot had blocked a major artery in the brain -- but we just had no way of dissolving it.
It took medical research to figure out how clots form and dissolve. Then the huge research breakthrough called recombinant DNA technology allowed us to make large amounts of natural substances like tPA. Without this research, most of it supported by your tax dollars, we would not have tPA, human insulin, or many other life-saving medicines. Think about that when you read about cuts in funding for medical research.
• Dr. Komaroff is a physician and professor at Harvard Medical School. Send questions to AskDoctorK.com.