Evaluation of the Duration of Therapy for Thrombosis in Children

Children (birth to 21 years of age, inclusive) with first-episode venous thrombosis in association with a reversible clinical trigger (key exclusions: history of cancer; severe thrombophilia state disclosed) are enrolled and prescribed anticoagulation according to the clinical standard of care and American College of Physicians (Chest journal) 2012 recommendations. At the 6 week (post-diagnosis) follow-up visit, repeat radiologic imaging is performed to determine residual thrombus burden and its degree of occlusion. In addition, those subjects with antiphospholipid antibodies (APA) disclosed at enrollment will undergo repeat APA testing.

Patients with residual occlusive thrombosis or persistent APA are excluded from randomization, and followed on parallel cohort arms (observational), with conventional anticoagulation durations. All other patients are randomized to a total anticoagulant duration of 6 weeks versus 3 months. Children are followed for primary efficacy endpoints of symptomatic recurrent venous thromboembolism (VTE) and primary safety endpoints of clinically-relevant bleeding (major plus clinically-relevant non-major, as per International Society of Thrombosis and Haemostasis Scientific and Standardization Committee [Journal of Thrombosis \& Haemostasis] 2012 definitions/recommendations).

Children are followed through 2 years (with primary endpoint at 1 year). Those with deep venous thromboses affecting venous return from the limbs also undergo standardized post-thrombotic syndrome (PTS) outcome assessment using the Manco-Johnson pediatric PTS instrument.

The non-inferiority analysis uses a bivariate endpoint approach, modeling the inherent clinical trade-off between the risks of recurrent VTE and bleeding. The trial will enroll 750 children across 40 participating centers, and allows for a 25% rate of exclusion from the per-protocol population due to randomization non-eligibility (i.e. parallel cohort), withdrawal/loss to follow-up, and protocol non-adherence.

A sub-study, completed in late 2013, used investigational dalteparin in lieu of formulary low molecular weight heparin (typically enoxaparin) in those children who were clinically prescribed a low molecular weight heparin for sub-acute anticoagulation. The goal of this sub-study was to report dose-finding and outcomes data in children treated with dalteparin for VTE. Outcomes in these patients were qualitatively compared with those of patients who received enoxaparin, warfarin, or other anticoagulants for sub-acute anticoagulation. This portion of the study was an industry-sponsored investigator-initiated sub-study with an investigator-held IND. Since the closure of the sub-study, the overall Kids-DOTT study is no longer conducted under an Investigational New Drug (IND) application.

Principal aims and hypotheses:

Specific Aim #1: To evaluate the efficacy and safety of shortened-duration (6 weeks total) versus conventional-duration (3 months total) anticoagulation for first-episode, provoked, acute venous thrombosis among children in whom thrombus resolution/non-occlusion (i.e. established blood flow) is evident after the initial 6 weeks of anticoagulant therapy

Hypothesis: Among children with first-episode, provoked, acute venous thrombosis in whom thrombosis is resolved or non-occlusive at six weeks follow-up, a shortened duration of anticoagulation (total six weeks; i.e. no further therapy) is non-inferior in efficacy to the conventional duration (total three months) of anticoagulation with respect to the risk of symptomatic recurrent VTE at 1 year, and is superior in safety with respect to the risk of clinically-relevant bleeding.(The hypothesis will also be tested in secondary analysis at 2 years, using the same efficacy and safety outcomes as for the 1 year primary analysis.)

Specific Aim #2: To compare the composite efficacy of shortened-duration (6 weeks total) versus conventional-duration (3 months total) anticoagulation for first-episode, provoked, acute venous thrombosis among children in whom thrombus resolution/non-occlusion (i.e., blood flow) is evident after the initial 6 weeks of anticoagulant therapy.

Hypothesis: Among children with first-episode, provoked, acute venous thrombosis in whom thrombosis is resolved or non-occlusive at six weeks follow-up, a shortened duration of anticoagulation (total six weeks; i.e. no further therapy) is non-inferior to the conventional duration (total three months) of anticoagulation with respect to a composite efficacy endpoint comprised of the 1-year risk of symptomatic recurrent VTE or PTS. (The hypothesis will also be tested in secondary analysis at 2 years.)

Specific Aim #3: To determine whether outcomes of first-episode, provoked, acute venous thrombosis (specifically, with respect to recurrent VTE and PTS) among children treated with conventional-duration (3 months total) anticoagulation differ between those with and without thrombus resolution/non-occlusion at 6 weeks.

Hypothesis: Among children with first-episode, provoked, acute venous thrombosis treated with conventional-duration (3 months total) anticoagulation, the cumulative incidences of recurrent VTE and PTS are significantly lower among those in whom thrombus resolution/non-occlusion was, versus was not, evident after the initial 6 weeks of anticoagulant therapy.

Specific Aim #4: To establish a clinical trial-derived plasma and nucleic acids biorepository for future proteomic, genomic, and metabolomic investigations of predictors and modulators of VTE outcomes in children.

Specific Aim #5: To investigate whether duration of anticoagulation (over the range of 3 months to indefinite duration, as determined clinically in routine care) on influences the risks of symptomatic recurrent VTE and clinically-relevant bleeding among children with first-episode, provoked, acute venous thrombosis in whom persistent antiphospholipid antibody (APA) positivity is evident at 6- and 12 -weeks post-diagnosis.

Hypothesis: Among children with first-episode, provoked, acute venous thrombosis in whom persistent APA positivity is evident at 6- and 12 -weeks post-diagnosis, duration of anticoagulant therapy is not a predictor of symptomatic recurrent VTE but is directly related to the risk of clinically-relevant bleeding.

Specific Aim #6 (Exploratory Aim): To evaluate whether the effect of treatment duration on the risks of symptomatic recurrent VTE and clinically-relevant bleeding in children with first-episode, provoked, acute venous thrombosis differs substantively between subgroups defined by type of sub-acute anticoagulant therapy in real-world clinical use (all prescribed clinically, with the exception of investigational dalteparin, which was prescribed under an investigator-held IND through December 2013).