Pediatric High-Risk Deep Venous Thrombosis Lytic Outcomes Trial (PHLO)

University of Colorado Denver (CU Denver) logo

University of Colorado Denver (CU Denver)

Status and phase

Phase 3


Deep Vein Thrombosis
Venous Thrombosis
Post-Thrombotic Syndrome


Drug: Recombinant tissue plasminogen activator (rt-PA)
Drug: Standard Anticoagulation Therapy

Study type


Funder types



ML29463 (Other Identifier)

Details and patient eligibility


The purpose of this study is to determine if the use of adjunctive catheter-directed thrombolysis (CDT), which includes the intrathrombus administration of rt-PA (Activase/Alteplase), can prevent post-thrombotic syndrome (PTS) in pediatric patients with symptomatic proximal deep vein thrombosis (DVT) as compared with optimal standard anticoagulation alone.

Full description

rt-PA, the study drug, is a fibrinolytic drug that is indicated for use in acute myocardial infarction, acute ischemic stroke, and acute massive pulmonary embolism in adults. Previous studies have shown the ability of rt-PA to lyse venous thrombus in patients with deep vein thrombosis (DVT), and suggest that successful rt-PA mediated thrombolysis can prevent post-thrombotic syndrome (PTS). rt-PA is delivered directly into venous thrombus using a catheter/device which is embedded within the thrombus by a physician under imaging guidance. This method of rt-PA delivery, catheter-directed thrombolysis (CDT), is thought to be safer, more effective, and more efficient than previous methods. The question of whether CDT using rt-PA improves long-term DVT patient outcomes with acceptable risk and cost is currently being studied in the ATTRACT Trial for adults, but has not yet been addressed in the pediatric population. The rationale for performing the PHLO Trial is based upon: the major burden of PTS on pediatric DVT patients and the U.S. healthcare system the reported association between rapid clot lysis and prevention of PTS the proven ability of rt-PA to dissolve venous thrombus in proximal DVT the recent advances in CDT methods which may lower bleeding risk, but which could, inadvertently, cause more endothelial injury in the smaller caliber vessels of pediatric patients the lack of outcome evidence for either anticoagulation or catheter-directed thrombolysis in children the major clinical controversy on whether CDT should routinely be used for first-line DVT therapy




6 to 21 years old


No Healthy Volunteers

Inclusion criteria

* Subject and/or legal guardian has voluntarily provided signed informed consent. * Subject is 6-21 years old with a minimum weight of 20 kg at the time of enrollment. * Radiologically-confirmed, symptomatic proximal lower extremity DVT involving the inferior vena cava, iliac vein, and/or common femoral vein; DVT must be occlusive in at least one involved vein * Life expectancy greater than or equal to 2 years.

Exclusion criteria

* Symptom duration \> 14 days for DVT episode in affected leg * Known history of a bleeding disorder * Known history of heparin-induced thrombocytopenia (HIT) * Prior established diagnosis of PTS in lower extremities * Circulatory compromise necessitating surgery * Pulmonary embolism with hemodynamic compromise or other acute illness precluding tolerance of catheter-directed therapy * Severe hypersensitivity or allergy to Activase(R), iodinated contrast or planned treatment anticoagulant drug, except for mild-moderate contrast allergies for which steroid pre-treatment can be used. * Inability to maintain hemoglobin \<9.0 mg/dL, INR \>1.7, or platelets \<100,000/mL, using transfusion as indicated. * Active or historic bleeding, vasculopathy, coagulopathy, invasive procedure or medical condition contraindicating thrombolysis or anticoagulation * Previous thrombolysis within the last month * Pregnant female or within 7 days of uncomplicated delivery * Participation in another investigational study within the last month * Life expectancy \< 2 years or with chronic non-ambulatory status * Inability to provide informed consent or to comply with study assessments

Trial design

Primary purpose




Interventional model

Parallel Assignment


None (Open label)

0 participants in 2 patient groups

Standard Anticoagulation Therapy
Active Comparator group
Anticoagulant therapy will be prescribed in accordance with 2012 ACCP Guidelines for children. Initial therapy generally will consist of low molecular weight heparin (LMWH) or unfractionated heparin (UFH), monitored to achieve and maintain a target anti-Xa activity of 0.5-1.0 IU/mL for LMWH and 0.35-0.7 IU/mL for UFH. Long-term therapy generally will consist of warfarin/coumadin, monitored to achieve and maintain a target INR of 2.0-3.0. The use of novel anticoagulants is permitted based on investigator preference.
Drug: Standard Anticoagulation Therapy
Catheter-Directed Thrombolysis
Experimental group
Catheter-Directed Thrombolysis (CDT) with intrathrombus delivery of Recombinant tissue plasminogen activator (rt-PA) (maximum allowable total dose 35 mg/24 hours) into the DVT over a period of up to 24 hours. CDT will be initiated within 72 hours of diagnosis. Two methods of initial rt-PA delivery will be used: 1.) AngioJet Thrombectomy System- maximum first-session rt-PA dose 25 mg; or 2.) Catheter-directed rt-PA infusion for up to 24 hours at 0.01 mg/kg/hr (maximum 1.0 mg/hr) via a multisidehole catheter. Before and after CDT, patients will receive standard DVT therapy as in the standard anticoagulation group
Drug: Recombinant tissue plasminogen activator (rt-PA)

Trial contacts and locations



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