PEITHO-3. Reduced-dose thrombolytic treatment for patients with higher-intermediate risk acute pulmonary embolism.

When a patient is diagnosed with blood clots in the lung (pulmonary embolism or 'PE'), the treatment is blood thinners. Additional treatment they receive is guided by how severe the blood clots are. Around a third of people diagnosed with PE can be categorized as intermediate risk and these patients have double the risk of dying within the next month. Currently these people are treated with injectable blood thinners. Very few patients have high risk PE and they are all given a powerful medication called thrombolysis. Thrombolysis breaks down the clot but can also cause bleeding (which may lead to death or stroke). Only one study has looked at using thrombolysis for intermediate risk patients with PE. This study found that the benefits of thrombolysis were offset by a higher rate of serious bleeding. Doctors are still looking for a better treatment for patients with intermediate risk PE to reduce the risk of death and to improve recovery. We will participate in an international study on intermediate risk PE patients who have a higher chance of dying. The study uses a reduced dose of the thrombolytic drug, instead of a full dose. This is a world-wide randomized controlled trial where each patient has an equal chance (like flipping a coin) of being given the thrombolytic drug or placebo (no drug). The reduced-dose study drug will be given in addition to the standard blood thinner treatment, so everyone will be given usual treatment. The study will determine if thrombolysis saves more lives than standard blood thinners alone. It will also report if thrombolysis causes more bleeding. It is important that Canada participates in this study because we need to know if this treatment helps Canadian patients. It is unlikely that such a large study will ever be done again because it requires so many hospitals in many countries to participate. The study results will guide how PE is treated in Canada in the future.