tPA quickly dissolves the clots that cause many strokes. By opening a blocked blood vessel and restoring blood flow, tPA can reduce the amount of damage to the brain that can occur during a stroke. To be effective, tPA and other drugs like it must be given within a few hours of the stroke symptoms beginning.

How effective are clot busters?

The investigators found that 22 percent of the patients treated with tenecteplase had more than 50 percent of blood flow return to the brain, compared with 10 percent of those treated with alteplase.

How long do clot busters take to work?

However, tPA has to be given within a certain time frame to work. Long-time guidelines stated that the drug should be infused within three hours of the first stroke symptoms -- or, for certain patients, within 4.5 hours.