Tissue Plasminogen Activator Therapy

Mechanism of Action

Alteplase functions within the endogenous fibrinolytic cascade by converting plasminogen to plasmin through hydrolysis of the arginine-valine bond in plasminogen. The activated plasmin subsequently degrades fibrin and fibrinogen, resulting in clot dissolution and the restoration of blood flow.[19][20] Notably, "tPA" refers to the endogenous tPA enzyme, not a specific therapeutic agent. Alteplase is the approved therapeutic agent, which is a recombinant, genetically modified form of tPA, also known as recombinant tissue-type plasminogen activator (rtPA).[21][22][23]

Pharmacokinetics

Absorption: Alteplase is administered via the IV route, resulting in immediate and complete systemic availability.

Distribution: The initial volume of distribution is approximately equal to the plasma volume.

Metabolism: Alteplase is primarily cleared through hepatic metabolism.

Excretion: Alteplase is rapidly cleared from the plasma, with an initial half-life of less than 5 minutes.

Administration

Available Dosage Forms and Strengths

Alteplase is available as a 2 mg lyophilized powder for catheter clearance. For systemic thrombolysis, it is supplied in single-dose vials of 50 mg and 100 mg lyophilized powder, each accompanied by 50 mL or 100 mL of sterile water for reconstitution.

Adult Dosage (FDA-Approved Indications)

Pulmonary embolism: An alteplase dose of 100 mg should be administered over 2 hours, typically as a 10 mg bolus followed by a 90 mg infusion over 2 hours.

Ischemic stroke: Prompt evaluation and treatment are critical when administering alteplase for acute ischemic stroke.

• Before initiating therapy, a non-contrast CT (NCCT) scan should be obtained to rule out intracranial hemorrhage, and vital signs must be stabilized. Before administering tPA, a blood glucose test is required.[24] If the patient is on anticoagulation therapy, such as warfarin, prothrombin time (PT), partial thromboplastin time (PTT), and international normalized ratio (INR) should be measured. The effectiveness of tPA is highly time-dependent; earlier administration is associated with better outcomes. 
• The maximum recommended dose of alteplase for ischemic stroke is 90 mg. 
  • For patients with a body weight of 100 kilograms or less, the recommended regimen is 0.09 mg/kg (10% of the total 0.9 mg/kg dose) administered as an IV bolus over 1 minute, followed by 0.81 mg/kg (90% of the 0.9 mg/kg dose) as a continuous infusion over 60 minutes.
  • For patients with a body weight of 100 kilograms or more, a fixed dose of 9 mg (10% of 90 mg) is given as an IV bolus over 1 minute, followed by 81 mg (90% of 90 mg) as a continuous infusion over 60 minutes.

ST-segment elevation myocardial infarction: For the treatment of STEMI, alteplase should be administered as soon as possible, ideally within 30 minutes of hospital arrival. Dosage is based on the patient's weight, as mentioned below.

• Adults with a body weight of 67 kg or more should receive a total dosage of 100 mg as follows: 15 mg IV bolus, followed by 50 mg IV infusion over 30 minutes, then 35 mg IV infusion over the next 60 minutes.
• Adults with a body weight of 67 kg or less should receive a 15 mg IV bolus, followed by an IV infusion of 0.75 mg/kg IV (not to exceed 50 mg) over 30 minutes, and then 0.5 mg/kg IV (not to exceed 35 mg) over the next 60 minutes.

Intravenous catheter occlusion: Alteplase (2 mg) should be instilled into the occluded lumen, followed by a 2-hour dwell time. This dosage may be repeated once if the initial attempt is unsuccessful. The use of alteplase in doses exceeding 4 mg for this indication has not been studied.

Adult Dosage (Off-Label Indications)

Catheter-directed therapy: Alteplase may be administered at a dose of 0.1 mg/kg/h, not to exceed 20 mg per 24 hours, for a duration of up to 96 hours.

Prosthetic valve thrombosis: Alteplase may be administered at a dose of 25 mg intravenously over 25 hours, repeated as necessary until a total dose of 200 mg is reached or resolution is confirmed by transesophageal echocardiography.

Alteplase is typically administered via the IV route as a bolus injection or continuous infusion. In emergency situations, intraosseous access may be used as an alternative route of administration.

Pediatric Dosage (Off-Label Indications)

Pediatric pleural effusions: A dose of 4 mg of alteplase diluted in 30 to 50 mL of 0.9% sodium chloride solution may be administered intrapleurally via chest tube. The solution is allowed to dwell for 1 hour and may be given as a single dose or as multiple doses at 24-hour intervals.

Specific Patient Populations

Hepatic impairment: No specific dosage adjustments have been established for patients with hepatic impairment. However, as alteplase is primarily cleared by the liver, impaired hepatic function may reduce its clearance, leading to increased systemic exposure. Close clinical monitoring is recommended in these patients.

Renal impairment: Alteplase is not primarily eliminated via the kidneys; therefore, no dosage adjustment is necessary for patients with renal impairment. 

Pregnancy considerations: Data on the use of alteplase in pregnant women are insufficient to determine the risk of drug-associated adverse developmental outcomes. Animal studies have shown embryocidal effects. Alteplase should be used during pregnancy only when the potential benefits justify the possible risks to the fetus. Additionally, pregnancy may increase the risk of bleeding complications associated with thrombolytic therapy. 

Breastfeeding considerations: tPA is naturally present in human colostrum and breast milk, with the highest levels observed during the early stages of lactation. Due to its significant molecular weight and probable degradation in the infant’s gastrointestinal tract, systemic absorption of alteplase by the infant is unlikely. However, clinical data on the use of alteplase during breastfeeding are limited. Caution is advised, particularly for newborns and preterm infants.[25] A risk-benefit assessment should guide decisions on whether to continue breastfeeding.

Pediatric patients: The safety and effectiveness of systemic alteplase use in pediatric patients have not been established, and it is not FDA-approved for this indication. However, the FDA has approved low-dose alteplase for the treatment of CVC occlusions in pediatric patients.

Older patients: Advanced age should be considered in the risk-benefit assessment, but is not a contraindication to therapy. Although older patients, particularly those aged 80 or older, experience less favorable outcomes, higher mortality rates, and an increased incidence of intracranial hemorrhage compared to younger patients, intravenous alteplase still provides a greater likelihood of achieving independence at 3 months across all age groups.[26]

Adverse Effects

The most frequent severe adverse events associated with the administration of tPA are related to bleeding.[27][28][29]

Bleeding associated with alteplase therapy can be broadly categorized into 2 categories—internal and superficial.

• Internal bleeding includes intracranial bleeding (ranging from 0.4% to 15.4%), retroperitoneal bleeding (<1%), gastrointestinal bleeding (5%), genitourinary bleeding (4%), and respiratory bleeding.
• Superficial or surface bleeding primarily occurs at invaded or disturbed sites of tissue disruption, such as venous cutdowns, arterial punctures, and recent surgical wounds.
• Less serious spontaneous bleeding events may include ecchymosis (1%), gingival bleeding (<1%), and epistaxis (<1%).

In clinical studies involving adult patients with acute ischemic stroke (n=624), the incidence of intracranial bleeding—particularly symptomatic intracranial hemorrhage—was significantly higher in patients treated with alteplase compared to those receiving placebo (total intracranial bleeding: 15.4% versus 6.4%, P<.01; symptomatic intracranial bleeding: 8% versus 1.3%, P<.01). Despite this increased risk, there was no corresponding rise in 90-day mortality or severe disability among patients treated with alteplase. Studies indicate that the incidence of intracranial bleeding is dose-dependent, with the highest incidence observed at a dose of 150 mg (1.3%) compared to 100 mg (0.4%). Overall, the rate of adverse events, including bleeding, appears to correlate with the total cumulative exposure to tPA.

Cardiac dysrhythmias may occur during tPA administration for non-STEMI and are typically related to the restoration of tissue perfusion rather than direct drug effects.

Allergic reactions, including anaphylactic-type responses, may occur following exposure to tPA. The antigenicity of tPA can vary depending on its source. The rapid conversion of plasminogen to plasmin can trigger the complement cascade, leading to mast cell degranulation and, subsequently, an anaphylactic reaction.

Drug-Drug Interactions

Heparin: Heparin is commonly coadministered with alteplase, particularly in the treatment of STEMI and massive pulmonary embolism. Although this combination may enhance thrombolytic efficacy, it also significantly increases the risk of bleeding, including delayed hemorrhage. Heparin should be administered as a carefully titrated continuous infusion, with close monitoring of coagulation parameters such as activated partial thromboplastin time (aPTT). In the setting of acute ischemic stroke, heparin is typically withheld for at least 24 hours following alteplase administration unless there is a specific clinical indication.

P2Y12 inhibitors: P2Y12 inhibitors (such as clopidogrel, prasugrel, and ticagrelor) may be initiated after alteplase administration for myocardial infarction or as part of secondary stroke prevention following thrombolysis. However, concurrent use during or immediately after alteplase infusion is generally avoided due to the increased risk of bleeding. In stroke patients, delayed initiation—typically 24 hours or more after alteplase administration—may be considered once follow-up neuroimaging confirms the absence of intracranial hemorrhage.

Oral anticoagulants: Therapeutic anticoagulation with warfarin (INR >1.7) or recent use of direct oral anticoagulants (such as apixaban, rivaroxaban, and dabigatran) is a contraindication to alteplase administration in ischemic stroke due to the increased risk of intracranial hemorrhage. In cases of acute myocardial infarction or pulmonary embolism, treatment decisions should be guided by the patient’s coagulation status and the timing of the last anticoagulant dose. Co-administration of alteplase and oral anticoagulants should occur only with careful monitoring and an individualized assessment of the bleeding risk versus the therapeutic benefit.

Glycoprotein IIb/IIIa inhibitors: These potent antiplatelet agents (such as abciximab, eptifibatide, and tirofiban) significantly increase the risk of bleeding when used in conjunction with alteplase. Their use may be considered in selected high-risk PCI settings under close hemostatic monitoring.

Nonsteroidal anti-inflammatory drugs: Nonsteroidal anti-inflammatory drugs (NSAIDs) inhibit platelet aggregation and may increase the risk of bleeding when used concurrently with alteplase. Although not an absolute contraindication, their use should be avoided during the peri-thrombolytic period unless clinically necessary.

Other fibrinolytics: Sequential or combined use of alteplase with other fibrinolytic agents (such as streptokinase, tenecteplase, reteplase, and urokinase) is contraindicated due to additive fibrinolytic effects and an increased risk of severe bleeding and hemorrhagic stroke. Alteplase should not be administered within 24 hours of treatment with another fibrinolytic.

Aspirin: Low-dose aspirin is a component of standard dual antiplatelet therapy in patients with acute coronary syndrome and may be administered before or shortly after alteplase administration. Although it can enhance thrombolytic efficacy, concurrent use increases the risk of gastrointestinal and intracranial bleeding.[30] In the setting of ischemic stroke, aspirin is generally withheld for 24 hours following alteplase administration unless specifically indicated.

Contraindications

In 2016, the AHA published updated guidelines outlining the inclusion and exclusion criteria for the use of tPA in the management of ischemic stroke.[26] The list below includes the most recent absolute and relative contraindications for therapy, as determined by the AHA.

Absolute Contraindications

• Significant head trauma or prior stroke within the past 3 months
• Clinical presentation suggestive of subarachnoid hemorrhage
• Arterial puncture at a non-compressible site within the past 7 days
• History of intracranial hemorrhage
• Presence of an intracranial neoplasm, arteriovenous malformation, or aneurysm
• Recent intracranial or intraspinal surgery
• Elevated blood pressure (systolic >185 mmHg or diastolic >110 mmHg)
• Active internal bleeding
• Acute bleeding diathesis, including but not limited to:
  • Platelet count less than 100,000/mm³
  • Heparin use within the past 48 hours with an elevated aPTT above the upper limit of normal
  • Current use of anticoagulants with an INR greater than 1.7 or PT greater than 15 seconds
  • Current use of direct thrombin inhibitors or direct factor Xa inhibitors with elevated sensitive laboratory parameters (eg, aPTT, INR, ecarin clotting time [ECT], thrombin time [TT], or specific anti–factor Xa activity assays)
  • Blood glucose concentration less than 50 mg/dL (2.7 mmol/L)
• CT demonstrates multilobar infarction (hypodensity involving more than one-third of a cerebral hemisphere)
• In cases of STEMI or pulmonary embolism, a recent history of stroke is a contraindication to TPA therapy [7]

Relative Contraindications

Recent evidence indicates that, in select cases and with careful evaluation of the risk-to-benefit ratio, fibrinolytic therapy may be administered despite the presence of one or more relative contraindications. The risks and benefits of IV rtPA administration should be thoroughly assessed when any of the following relative contraindications apply:

• Only minor or rapidly improving stroke symptoms (resolving spontaneously)
• Pregnancy
• Seizure at onset with postictal residual neurological impairments [31]
• Major surgery or severe trauma within the past 14 days
• Recent gastrointestinal or urinary tract hemorrhage (within the previous 21 days)
• Recent acute myocardial infarction (within the preceding 3 months)

Warning and Precautions 

Cholesterol embolization: Cholesterol embolism has been infrequently reported in patients receiving thrombolytic agents, and its actual incidence remains unknown. Clinical manifestations may include livedo reticularis (commonly referred to as "purple toe" syndrome) and acute kidney injury.[32][33][34]

Monitoring

No specific therapeutic drug monitoring guidelines exist for assessing the efficacy of tPA. When prolonged off-label therapy is necessary—such as with catheter-directed treatment or repeated dosing for valve thrombosis—serial imaging of the thrombus is appropriate. Safety monitoring should include PT, PTT, hemoglobin, and hematocrit to evaluate for ongoing bleeding. Fibrinogen levels below 150 mg/dL may indicate an increased risk of bleeding.

In STEMI, reperfusion is assessed using the Thrombolysis in Myocardial Infarction (TIMI) flow grade. For pulmonary embolism, therapeutic response is evaluated through measures such as right ventricular function, the right ventricle-to-left ventricle (RV/LV) ratio, and a reduction in pulmonary artery systolic pressure.[35] In ischemic stroke, the National Institutes of Health Stroke Scale (NIHSS) is used to gauge neurological improvement following alteplase administration, whereas the Modified Rankin Scale (mRS) and Barthel Index (BI) are used to monitor long-term functional outcomes.[36]

Toxicity

Signs and Symptoms of Overdose

Alteplase overdose may manifest as significant internal or external bleeding, particularly at arterial or venous puncture sites. Intramuscular injections and unnecessary trauma should be avoided during therapy. If arterial access is required while alteplase is being infused, a compressible upper extremity vessel should be used, with firm pressure applied for at least 30 minutes, followed by close monitoring. The concomitant use of anticoagulants such as heparin and aspirin increases bleeding risk and requires close monitoring. Intracranial hemorrhage should be suspected in the presence of new-onset headache, nausea, or vomiting.[37] In acute ischemic stroke, inaccurate weight-based dosing, especially overdosing due to overestimated body weight, has been linked to a higher risk of intracranial hemorrhage and worse functional outcomes. These findings underscore the crucial importance of accurate weight measurement before administering alteplase.[38]

Management of Overdose

No specific reversal agent exists for the potentially severe bleeding associated with tPA therapy. Alteplase should be discontinued immediately upon recognition of overdose or major bleeding. Management strategies commonly include antifibrinolytic agents such as tranexamic acid or aminocaproic acid, although specific dosing guidelines have not been established. When fibrinogen levels fall below 150 mg/dL, administration of fresh frozen plasma or cryoprecipitate may offer additional benefit. Prompt use of cryoprecipitate is recommended, with close monitoring of fibrinogen levels throughout treatment.[37]

Enhancing Healthcare Team Outcomes

Thrombolytic agents have proven efficacy in the treatment of acute ischemic stroke, massive pulmonary embolism, and STEMI. Effective use of these agents requires healthcare professionals, including physicians, advanced practice providers, nurses, pharmacists, and radiologists, to possess a comprehensive understanding of the indications and contraindications relevant to their specialties. In acute ischemic stroke, neurologists lead the decision-making process for alteplase administration by integrating rapid imaging assessment with eligibility criteria. For pulmonary embolism with hemodynamic compromise, critical care physicians are responsible for guiding the use of alteplase. Advanced practice providers, including physician assistants and nurse practitioners, play a crucial role in implementing protocols and monitoring patients.

Effective thrombolytic therapy depends not only on timely administration but also on careful patient assessment to identify and rule out potential contraindications. Nurses are responsible for educating patients about the procedure and closely monitoring for bleeding complications. Pharmacists must stay informed about novel anticoagulants and assess for potential drug interactions with thrombolytic agents. Coordination, multidisciplinary collaboration, clear communication, and ongoing vigilance among all healthcare professionals are essential to prevent serious complications associated with thrombolytic therapy.[4][39]

Outcomes

Numerous clinical trials have evaluated the effectiveness of thrombolytic agents in patients with acute myocardial infarction, pulmonary embolism, acute ischemic limb, and embolic stroke. When used to treat acute myocardial infarction, ischemic stroke, and pulmonary embolism, these agents generally yield fair to good outcomes. The most significant limitation of thrombolytic therapy is the delay in patient arrival to the emergency department or delayed diagnosis. Despite this, thrombolytic drugs have saved many lives, are cost-effective, and contribute to reduced hospital stays.[40][41][28]