conjunction with aspirin and heparin. An accelerated infusion of alteplase was found to significantly reduce mortality in comparison to a non-accelerated infusion, though it also slightly increases the risk of major bleeding. Alteplase should not be used in cases of acute coronary syndrome other than STEMI. Pulmonary embolism As of 2019, alteplase is the most commonly used medication to treat pulmonary embolism (PE). Alteplase has a short infusion time of 2 hours and a half-life of 4–6 minutes. Alteplase has been approved by the FDA, and treatment can be done via systemic thrombolysis or catheter-directed thrombolysis. Systemic thrombolysis can quickly restore right ventricular function, heart rate, and blood pressure in patients with acute PE. However, standard doses of alteplase used in systemic thrombolysis may lead to massive bleeding, such as intracranial hemorrhage, particularly in older patients. A systematic review has shown that low-dose alteplase is safer than and as effective as the standard amount. Catheter-directed thrombolysis may be more efficient than systemic thrombolysis, as alteplase is locally administered to the occlusion site, and wash-away of the medication into other blood vessels is minimized. This procedure involves positioning a multi-sidehole catheter into the blood clot. Alteplase may be used to treat PE if patients have a high risk for complications, such as if: they are hypotensive with a systolic blood pressure less than 90 mmHg they are in cardiac arrest presumed to be caused by a pulmonary embolism their clinical exam shows signs of deterioration or worsening of symptoms Blocked catheters Alteplase can be used in small doses to clear blood clots that obstruct a catheter, reopening the catheter so it can continue to be used. Catheter obstruction is commonly observed with a central venous catheter. Currently, the standard treatment for catheter obstructions in the United States is alteplase administration. Alteplase is effective and low risk for treating blocked catheters in adults and children. Overall, adverse effects of alteplase for clearing blood clots are rare. Novel alternatives to treat catheter occlusion, such as tenecteplase, reteplase, and recombinant urokinase, offer the advantage of shorter dwell times than alteplase. Contraindications A person should not receive alteplase treatment if testing shows they are not suffering from an acute ischemic stroke or if the risks of treatment outweigh the likely benefits. Alteplase is contraindicated in those with bleeding disorders that increase a person's tendency to bleed and in those with an abnormally low platelet count.