The breakdown of a BLOOD CLOT by enzymic activity (see ENZYME). Naturally occurring enzymes limit the enlargement of clots, and drugs – for example, STREPTOKINASE or Alteplase– may be given to ‘dissolve’ clots (e.g. following a coronary THROMBOSIS – (see under HEART, DISEASES OF). The drug needs to be given within a few hours to be effective, so prompt diagnosis and transfer to hospital is essential: a short ‘door-to-needle’ time. An unwanted effect may be increased risk of bleeding, especially in the elderly. It has been used in trials in patients with PULMONARY EMBOLISM and with peripheral arterial disease, but its value in these conditions is uncertain.