Thrombolysis involves the administration of medication that activates the enzymes that normally destroy blood clots. Thrombolysis agents include streptokinase, reteplase, alteplase, and tenecteplase. If no contraindications are present (such as a high risk of bleeding), thrombolysis can be given in the pre-hospital or in-hospital setting. When given to people suspected of having a STEMI within 6 hours of the onset of symptoms, thrombolytic drugs save the life of 1 in 43 who received them. The risks were major bleeding (1 in 143) and brain bleeding (1 in 250). It is unclear whether pre-hospital thrombolysis reduces death in people with STEMI compared to in-hospital thrombolysis. Pre-hospital thrombolysis reduces time to thrombolytic treatment, based on studies conducted in higher income countries.

How many hours must pass after onset of symptoms before administering thrombolysis?