Publications by authors named "John M Kittelson"

22 Publications

  • Page 1 of 1

Effect of Anticoagulant Therapy for 6 Weeks vs 3 Months on Recurrence and Bleeding Events in Patients Younger Than 21 Years of Age With Provoked Venous Thromboembolism: The Kids-DOTT Randomized Clinical Trial.

JAMA 2022 01;327(2):129-137

Department of Obstetrics and Gynecology, I. M. Sechenov First Moscow State Medical University, Moscow, Russia.

Importance: Among patients younger than 21 years of age, the optimal duration of anticoagulant therapy for venous thromboembolism is unknown.

Objective: To test the hypothesis that a 6-week duration of anticoagulant therapy for provoked venous thromboembolism is noninferior to a conventional 3-month therapy duration in patients younger than 21 years of age.

Design, Setting, And Participants: Randomized clinical trial involving 417 patients younger than 21 years of age with acute, provoked venous thromboembolism enrolled at 42 centers in 5 countries from 2008-2021. The main exclusions were severe anticoagulant deficiencies or prior venous thromboembolism. Patients without persistent antiphospholipid antibodies and whose thrombi were resolved or not completely occlusive upon repeat imaging at 6 weeks after diagnosis underwent randomization. The final visit for the primary end points occurred in January 2021.

Interventions: Total duration for anticoagulant therapy of 6 weeks (n = 207) vs 3 months (n = 210) for provoked venous thromboembolism.

Main Outcomes And Measures: The primary efficacy and safety end points were centrally adjudicated symptomatic recurrent venous thromboembolism and clinically relevant bleeding events within 1 year blinded to treatment group. The primary analysis was noninferiority in the per-protocol population. The noninferiority boundary incorporated a bivariate trade-off that included an absolute increase of 0% in symptomatic recurrent venous thromboembolism with an absolute risk reduction of 4% in clinically relevant bleeding events (1 of 3 points on the bivariate noninferiority boundary curve).

Results: Among 417 randomized patients, 297 (median age, 8.3 [range, 0.04-20.9] years; 49% female) met criteria for the primary per-protocol population analysis. The Kaplan-Meier estimate for the 1-year cumulative incidence of the primary efficacy outcome was 0.66% (95% CI, 0%-1.95%) in the 6-week anticoagulant therapy group and 0.70% (95% CI, 0%-2.07%) in the 3-month anticoagulant therapy group, and for the primary safety outcome, the incidence was 0.65% (95% CI, 0%-1.91%) and 0.70% (95% CI, 0%-2.06%). Based on absolute risk differences in recurrent venous thromboembolism and clinically relevant bleeding events between groups, noninferiority was demonstrated. Adverse events occurred in 26% of patients in the 6-week anticoagulant therapy group and in 32% of patients in the 3-month anticoagulant therapy group; the most common adverse event was fever (1.9% and 3.4%, respectively).

Conclusions And Relevance: Among patients younger than 21 years of age with provoked venous thromboembolism, anticoagulant therapy for 6 weeks compared with 3 months met noninferiority criteria based on the trade-off between recurrent venous thromboembolism risk and bleeding risk.

Trial Registration: ClinicalTrials.gov Identifier: NCT00687882.
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http://dx.doi.org/10.1001/jama.2021.23182DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8753509PMC
January 2022

Treatment-Dose LMWH versus Prophylactic/Intermediate Dose Heparins in High-Risk COVID-19 Inpatients: Rationale and Design of the HEP-COVID Trial.

Thromb Haemost 2021 Dec 6;121(12):1684-1695. Epub 2021 Apr 6.

Institute of Health Innovations and Outcomes Research, The Feinstein Institutes for Medical Research, Northwell Health, Manhasset, New York, United States.

Coronavirus disease-2019 (COVID-19) has been associated with significant risk of venous thromboembolism (VTE), arterial thromboembolism (ATE), and mortality particularly among hospitalized patients with critical illness and elevated D-dimer (Dd) levels. Conflicting data have yet to elucidate optimal thromboprophylaxis dosing. HEP-COVID (NCT04401293) is a phase 3, multicenter, pragmatic, prospective, randomized, pseudo-blinded, active control trial to evaluate efficacy and safety of therapeutic-dose low-molecular-weight heparin (LMWH) versus prophylactic-/intermediate-dose LMWH or unfractionated heparin (UFH) for prevention of a primary efficacy composite outcome of VTE, ATE, and all-cause mortality 30 ± 2 days post-enrollment. Eligible patients have COVID-19 diagnosis by nasal swab or serologic testing, requirement for supplemental oxygen per investigator judgment, and Dd >4 × upper limit of normal (ULN) or sepsis-induced coagulopathy score ≥4. Subjects are randomized to enoxaparin 1 mg/kg subcutaneous (SQ)/two times a day (BID) (creatinine clearance [CrCl] ≥ 30 mL/min) or 0.5 mg/kg (CrCl 15-30 mL/min) versus local institutional prophylactic regimens including (1) UFH up to 22,500 IU (international unit) daily (divided BID or three times a day), (2) enoxaparin 30 and 40 mg SQ QD (once daily) or BID, or (3) dalteparin 2,500 IU or 5,000 IU QD. The principal safety outcome is major bleeding. Events are adjudicated locally. Based on expected 40% relative risk reduction with treatment-dose compared with prophylactic-dose prophylaxis, 308 subjects will be enrolled (assuming 20% drop-out) to achieve 80% power. Distinguishing design features include an enriched population for the composite endpoint anchored on Dd >4 × ULN, stratification by intensive care unit (ICU) versus non-ICU, and the ability to capture asymptomatic proximal deep venous thrombosis via screening ultrasonography prior to discharge.
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http://dx.doi.org/10.1055/a-1475-2351DOI Listing
December 2021

Group sequential designs for clinical trials with bivariate endpoints.

Stat Med 2020 11 10;39(26):3823-3839. Epub 2020 Aug 10.

Department of Biostatistics and Informatics, Colorado School of Public Health, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA.

Although all clinical trials are designed and monitored using more than one endpoint, methods are needed to assure that decision criteria are chosen to reflect the clinically relevant tradeoffs that assure the trial's scientific integrity. This article presents a framework for the design and monitoring clinical trials in a bivariate outcome space. The framework uses a rectangular hyperbola to define a bivariate null curve that divides outcome space into regions of benefit and lack of benefit. The curve is shown to be a flexible mapping of bivariate space that allows a continuous tradeoff between the two endpoints in a manner that captures many previous bivariate designs. The curve is extended to a distance function in bivariate space that allows different decisions in each of the four quadrants that comprise bivariate space. The distance function forms a statistic ( ); the distribution of its estimate is derived and used as a basis for trial design and group sequential monitoring plans in bivariate space. A recursive form of the bivariate group sequential density is used to evaluate and control operating characteristics for the proposed design. The bivariate designs are shown to meet or exceed the usual standards for size and power. The proposed design is illustrated in the ongoing NHLBI-sponsored Kids-DOTT multinational randomized controlled trial comparing shortened versus conventional anticoagulation for the treatment of venous thromboembolism in patients less than 21 years of age. The proposed methods are broadly applicable to a wide range of clinical settings and trial designs.
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http://dx.doi.org/10.1002/sim.8696DOI Listing
November 2020

Rivaroxaban in Peripheral Artery Disease after Revascularization.

N Engl J Med 2020 05 28;382(21):1994-2004. Epub 2020 Mar 28.

From Colorado Prevention Center (CPC) Clinical Research (M.P.B., M.R.N., W.H.C., L.D., N.J., C.N.H., W.R.H.), the Department of Medicine, Division of Cardiovascular Medicine (M.P.B., C.N.H., W.R.H.), the Department of Surgery, Division of Vascular Surgery (M.R.N.), and the Department of Medicine, Division of Endocrinology (W.H.C.), University of Colorado Anschutz Medical Campus, and the Department of Biostatistics and Informatics, Colorado School of Public Health (J.M.K.) - all in Aurora; the Department of Vascular Medicine, Klinikum Darmstadt, Darmstadt, and Center for Thrombosis and Hemostasis, University of Mainz, Mainz (R.M.B.), the Department of Vascular Medicine, Vascular Surgery-Angiology-Endovascular Therapy, University of Hamburg-Eppendorf, Hamburg (E.S.D.), and Bayer, Wuppertal (A.F.P., E.M.) - all in Germany; the Population Health Research Institute, Hamilton Health Sciences and McMaster University, Hamilton, ON, Canada (S.S.A.); Duke Clinical Research Institute, Division of Cardiology, Duke University, Durham, NC (M.R.P.); the Vascular and Interventional Radiology Department, Careggi University Hospital, University of Florence, Florence, Italy (F.F.); Ivano-Frankivsk National Medical University, Ivano-Frankivsk, Ukraine (I.G.); B-A-Z County University Teaching Hospital, Miskolc, Hungary (L.M.); University of Latvia, Pauls Stradins University Hospital, Riga (D.K.K.); ECLA (Estudios Clínicos Latino América), ICR (Instituto Cardiovascular de Rosario), Rosario, Argentina (R.D.); the Division of Angiology, Medical University Graz, Graz, Austria (M.B.); and Janssen Research and Development, Raritan (L.P.H.), and Thrombosis Group Head, Clinical Development, Bayer U.S., Whippany (S.D.B.) - both in New Jersey.

Background: Patients with peripheral artery disease who have undergone lower-extremity revascularization are at high risk for major adverse limb and cardiovascular events. The efficacy and safety of rivaroxaban in this context are uncertain.

Methods: In a double-blind trial, patients with peripheral artery disease who had undergone revascularization were randomly assigned to receive rivaroxaban (2.5 mg twice daily) plus aspirin or placebo plus aspirin. The primary efficacy outcome was a composite of acute limb ischemia, major amputation for vascular causes, myocardial infarction, ischemic stroke, or death from cardiovascular causes. The principal safety outcome was major bleeding, defined according to the Thrombolysis in Myocardial Infarction (TIMI) classification; major bleeding as defined by the International Society on Thrombosis and Haemostasis (ISTH) was a secondary safety outcome.

Results: A total of 6564 patients underwent randomization; 3286 were assigned to the rivaroxaban group, and 3278 were assigned to the placebo group. The primary efficacy outcome occurred in 508 patients in the rivaroxaban group and in 584 in the placebo group; the Kaplan-Meier estimates of the incidence at 3 years were 17.3% and 19.9%, respectively (hazard ratio, 0.85, 95% confidence interval [CI], 0.76 to 0.96; P = 0.009). TIMI major bleeding occurred in 62 patients in the rivaroxaban group and in 44 patients in the placebo group (2.65% and 1.87%; hazard ratio, 1.43; 95% CI, 0.97 to 2.10; P = 0.07). ISTH major bleeding occurred in 140 patients in the rivaroxaban group, as compared with 100 patients in the placebo group (5.94% and 4.06%; hazard ratio, 1.42; 95% CI, 1.10 to 1.84; P = 0.007).

Conclusions: In patients with peripheral artery disease who had undergone lower-extremity revascularization, rivaroxaban at a dose of 2.5 mg twice daily plus aspirin was associated with a significantly lower incidence of the composite outcome of acute limb ischemia, major amputation for vascular causes, myocardial infarction, ischemic stroke, or death from cardiovascular causes than aspirin alone. The incidence of TIMI major bleeding did not differ significantly between the groups. The incidence of ISTH major bleeding was significantly higher with rivaroxaban and aspirin than with aspirin alone. (Funded by Bayer and Janssen Pharmaceuticals; VOYAGER PAD ClinicalTrials.gov number, NCT02504216.).
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http://dx.doi.org/10.1056/NEJMoa2000052DOI Listing
May 2020

Rationale and design for the Vascular Outcomes study of ASA along with rivaroxaban in endovascular or surgical limb revascularization for peripheral artery disease (VOYAGER PAD).

Am Heart J 2018 05 3;199:83-91. Epub 2018 Feb 3.

CPC Clinical Research, Aurora, CO; University of Colorado School of Medicine, Division of Cardiology, University of Colorado Denver, Aurora, CO. Electronic address:

Background: Patients with peripheral artery disease (PAD) undergoing a lower-extremity revascularization are at heightened risk for ischemic cardiac and limb events. Although intensification of antithrombotic therapy after revascularization has demonstrated benefit in coronary disease populations, this approach has not been well studied or shown consistent benefit in PAD. Recent trial evidence demonstrated that a treatment strategy of rivaroxaban added to background antiplatelet therapy reduced ischemic risk in patients following recent acute coronary syndromes, as well as in patients with stable atherosclerotic vascular disease. Whether these benefits extend to the population of patients with symptomatic lower-extremity PAD undergoing revascularization is the objective of the VOYAGER PAD trial.

Study Design: VOYAGER PAD is an international randomized, double-blind, placebo-controlled trial to evaluate the efficacy and safety of rivaroxaban in symptomatic PAD patients undergoing a peripheral surgical and/or endovascular revascularization. Patients are randomized in a 1:1 ratio to either rivaroxaban 2.5 mg twice daily or placebo, on a background of low-dose aspirin (100 mg daily). In addition, the use of a limited course of P2Y inhibition is allowed at the discretion of the site investigator. The primary efficacy end point is a novel composite of myocardial infarction, ischemic stroke, cardiovascular death, acute limb ischemia, and major amputation of vascular etiology. The primary safety end point is major bleeding according to the Thrombolysis in Myocardial Infarction definition. Enrolment began in August 2015 and will complete randomization of at least 6,500 patients by January 2018. This event-driven trial is expected to observe outcomes over a mean patient follow-up of 30 months.

Conclusions: VOYAGER PAD is evaluating the efficacy of rivaroxaban added to background antiplatelet therapy to reduce major cardiovascular and limb ischemic vascular outcomes in the high-risk population of PAD patients undergoing peripheral revascularization.
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http://dx.doi.org/10.1016/j.ahj.2018.01.011DOI Listing
May 2018

Bivariate evaluation of thromboembolism and bleeding in clinical trials of anticoagulants in patients with atrial fibrillation.

Thromb Haemost 2016 08 23;116(3):544-53. Epub 2016 Jun 23.

John M. Kittelson, Ph.D., Historic Building 500, Box B119, University of Colorado Anschutz Medical Campus, 13001 East 17th Place, Aurora, CO 80045, USA, Tel.: +1 303 724 4364, E-mail:

Clinical trials of antithrombotic therapy require a cohesive assessment of benefit and risk. A new graphical method to represent the bivariate relation of benefit and risk in trials of antithrombotic drugs is described and illustrated using published data from the four major registration clinical trials of non-vitamin K oral anticoagulants (NOACs) totalling 71,683 patients for prevention of thromboembolic events (TE) in patients with atrial fibrillation (RE-LY, ROCKET AF, ARISTOTLE, and ENGAGE-AF TIMI48). A curve representing a null hypothesis defines a region of benefit on a two-dimensional plane. Trial results are summarised by a rectangle defined by standard 95 % confidence intervals (CI) for thrombosis and bleeding risks. Benefit is judged by whether the confidence rectangle contains the null curve. The treatment effect is measured by the distance from the null curve to the opposing corners of the confidence rectangle (termed "corner distance (CD)"). Across trials NOACs reduced the absolute risk of TE compared to warfarin by 0.30 % (95 % CI: -0.56 % to -0.05 %) and reduced major bleeding by 0.88 % (95 % CI: -1.26 % to -0.51 %). Bivariate evaluation showed NOAC superiority to warfarin overall and elucidated dose differences; low dose edoxaban increased bivariate TE-bleeding risk 0.08 % (CD = -0.85 % to 0.78 %), whereas high dose edoxaban reduced risk 1.41 % (CD = -2.07 % to -0.70 %). In conclusion, bivariate evaluation facilitates visual assessment of the safety-efficacy profile of antithrombotic drugs. Its application to trials in atrial fibrillation found NOACs superior to warfarin without substantial differences between agents.
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http://dx.doi.org/10.1160/TH15-12-1000DOI Listing
August 2016

Improving evidence on anticoagulant therapies for venous thromboembolism in children: key challenges and opportunities.

Blood 2015 Dec 23;126(24):2541-7. Epub 2015 Oct 23.

Department of Pediatrics, Division of Cardiology, University of Alberta Faculty of Medicine, Edmonton, AB, Canada; and Stollery Children's Hospital, Edmonton, AB, Canada.

Venous thromboembolism (VTE) is increasingly diagnosed in pediatric patients, and anticoagulant use in this population has become common, despite the absence of US Food and Drug Administration (FDA) approval for this indication. Guidelines for the use of anticoagulants in pediatrics are largely extrapolated from large randomized controlled trials (RCTs) in adults, smaller dose-finding and observational studies in children, and expert opinion. The recently FDA-approved direct oral anticoagulants (DOACs), such as dabigatran, rivaroxaban, apixaban, and edoxaban, provide potential advantages over oral vitamin K antagonists and subcutaneous low-molecular-weight heparins (LMWHs). However, key questions arise regarding their potential off-label clinical application in pediatric thromboembolic disease. In this Perspective, we provide background on the use of LMWHs such as enoxaparin as the mainstay of treatment of pediatric provoked VTE; identify key questions and challenges with regard to DOAC trials and future DOAC therapy in pediatric VTE; and discuss applicable lessons learned from the recent pilot/feasibility phase of a large multicenter RCT of anticoagulant duration in pediatric VTE. The challenges and lessons learned present opportunities to improve evidence for anticoagulant therapies in pediatric VTE through future clinical trials.
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http://dx.doi.org/10.1182/blood-2015-06-651539DOI Listing
December 2015

Body composition and bone mineral density after ovarian hormone suppression with or without estradiol treatment.

Menopause 2015 Oct;22(10):1045-52

1Division of Geriatric Medicine, Department of Medicine, University of Colorado Anschutz Medical Campus, Aurora, CO 2Division of Endocrinology, Metabolism, and Diabetes, Department of Medicine, University of Colorado Anschutz Medical Campus, Aurora, CO 3Department of Biostatistics and Informatics, University of Colorado Anschutz Medical Campus, Aurora, CO 4Department of Clinical Pharmacy, University of Colorado Anschutz Medical Campus, Aurora, CO.

Objective: Suppression of ovarian hormones in premenopausal women on gonadotropin-releasing hormone agonist (GnRH(AG)) therapy can cause fat mass (FM) gain and fat-free mass (FFM) loss. Whether this is specifically caused by a decline in serum estradiol (E2) is unknown. This study aims to evaluate the effects of GnRH(AG) with placebo (PL) or E2 add-back therapy on FM, FFM, and bone mineral density (BMD). Our exploratory aim was to evaluate the effects of resistance exercise training on body composition during the drug intervention.

Methods: Seventy healthy premenopausal women underwent 5 months of GnRH(AG) therapy and were randomized to receive transdermal E2 (GnRH(AG) + E2, n = 35) or PL (GnRH(AG) + PL, n = 35) add-back therapy. As part of our exploratory aim to evaluate whether exercise can minimize the effects of hormone suppression, some women within each drug arm were randomized to undergo a resistance exercise program (GnRH(AG) + E2 + Ex, n = 12; GnRH(AG) + PL + Ex, n = 12).

Results: The groups did not differ in mean (SD) age (36 [8] and 35 [9] y) or mean (SD) body mass index (both 28 [6] kg/m). FFM declined in response to GnRH(AG) + PL (mean, -0.6 kg; 95% CI, -1.0 to -0.3) but not in response to GnRH(AG) + E2 (mean, 0.3 kg; 95% CI, -0.2 to 0.8) or GnRH(AG) + PL + Ex (mean, 0.1 kg; 95% CI, -0.6 to 0.7). Although FM did not change in either group, visceral fat area increased in response to GnRH(AG) + PL but not in response to GnRH(AG) + E2. GnRH(AG) + PL induced a decrease in BMD at the lumbar spine and proximal femur that was prevented by E2. Preliminary data suggest that exercise may have favorable effects on FM, FFM, and hip BMD.

Conclusions: Suppression of ovarian E2 results in loss of bone and FFM and expansion of abdominal adipose depots. Failure of hormone suppression to increase total FM conflicts with previous studies of the effects of GnRH(AG). Further research is necessary to understand the role of estrogen in energy balance regulation and fat distribution.
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http://dx.doi.org/10.1097/GME.0000000000000430DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4760356PMC
October 2015

Predicting functional performance and range of motion outcomes after total knee arthroplasty.

Am J Phys Med Rehabil 2014 Jul;93(7):579-85

From the Rueckert-Hartman College for Health Professions, School of Physical Therapy, Regis University, Denver, Colorado (MJB); Department of Biostatistics & Informatics, University of Colorado Anschutz Medical Campus, Colorado School of Public Health, Aurora, CO (JMK); and Department of Geriatrics (WMK) and Department of Physical Medicine and Rehabilitation (JES-L), University of Colorado Anschutz Medical Campus, School of Medicine.

Objective: The aim of this study was to assess the predictive value of functional performance and range of motion measures on outcomes after total knee arthroplasty.

Design: This is a secondary analysis of two pooled prospective randomized controlled trials. Sixty-four subjects (32 men and 32 women) with end-stage knee osteoarthritis scheduled to undergo primary total knee arthroplasty were enrolled. Active knee flexion and extension range of motion, Timed Up and Go (TUG) test time, and 6-min walk test distance were assessed.

Results: Preoperative measures of knee flexion and extension were predictive of long-term flexion (β = 0.44, P < 0.001) and extension (β = 0.46, P < 0.001). Acute measures of knee flexion and extension were not predictive of long-term flexion (β = 0.09, P = 0.26) or extension (β = 0.04, P = 0.76). Preoperative TUG performance was predictive of long-term 6-min walk performance (β = -21, P < 0.001). Acute TUG performance was predictive of long-term functional performance on the 6-min walk test, after adjusting for the effects of sex and age (P = 0.02); however, once adjusted for preoperative TUG performance, acute TUG was no longer related to long-term 6-min walk performance (P = 0.65).

Conclusions: Acute postoperative measures of knee range of motion are of limited prognostic value, although preoperative measures have some prognostic value. However, acute measures of functional performance are of useful prognostic value, especially when preoperative functional performance data are unavailable.
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http://dx.doi.org/10.1097/PHM.0000000000000065DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4350663PMC
July 2014

Amyloid precursor protein is an autonomous growth cone adhesion molecule engaged in contact guidance.

PLoS One 2013 14;8(5):e64521. Epub 2013 May 14.

Department of Pediatrics and Colorado Intellectual and Developmental Disabilities Research Center, University of Colorado School of Medicine, Aurora, Colorado, USA.

Amyloid precursor protein (APP), a transmembrane glycoprotein, is well known for its involvement in the pathogenesis of Alzheimer disease of the aging brain, but its normal function is unclear. APP is a prominent component of the adult as well as the developing brain. It is enriched in axonal growth cones (GCs) and has been implicated in cell adhesion and motility. We tested the hypothesis that APP is an extracellular matrix adhesion molecule in experiments that isolated the function of APP from that of well-established adhesion molecules. To this end we plated wild-type, APP-, or β1-integrin (Itgb1)- misexpressing mouse hippocampal neurons on matrices of either laminin, recombinant L1, or synthetic peptides binding specifically to Itgb1 s or APP. We measured GC adhesion, initial axonal outgrowth, and substrate preference on alternating matrix stripes and made the following observations: Substrates of APP-binding peptide alone sustain neurite outgrowth; APP dosage controls GC adhesion to laminin and APP-binding peptide as well as axonal outgrowth in Itgb1- independent manner; and APP directs GCs in contact guidance assays. It follows that APP is an independently operating cell adhesion molecule that affects the GC's phenotype on APP-binding matrices including laminin, and that it is likely to affect axon pathfinding in vivo.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0064521PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3653867PMC
December 2013

Estimation of treatment effect under non-proportional hazards and conditionally independent censoring.

Stat Med 2012 Dec 4;31(28):3504-15. Epub 2012 Jul 4.

Novartis Pharma AG, CH-4002, Basel, Switzerland.

In clinical trials with time-to-event outcomes, it is common to estimate the marginal hazard ratio from the proportional hazards model, even when the proportional hazards assumption is not valid. This is unavoidable from the perspective that the estimator must be specified a priori if probability statements about treatment effect estimates are desired. Marginal hazard ratio estimates under non-proportional hazards are still useful, as they can be considered to be average treatment effect estimates over the support of the data. However, as many have shown, under non-proportional hazard, the 'usual' unweighted marginal hazard ratio estimate is a function of the censoring distribution, which is not normally considered to be scientifically relevant when describing the treatment effect. In addition, in many practical settings, the censoring distribution is only conditionally independent (e.g., differing across treatment arms), which further complicates the interpretation. In this paper, we investigate an estimator of the hazard ratio that removes the influence of censoring and propose a consistent robust variance estimator. We compare the coverage probability of the estimator to both the usual Cox model estimator and an estimator proposed by Xu and O'Quigley (2000) when censoring is independent of the covariate. The new estimator should be used for inference that does not depend on the censoring distribution. It is particularly relevant to adaptive clinical trials where, by design, censoring distributions differ across treatment arms.
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http://dx.doi.org/10.1002/sim.5440DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3876422PMC
December 2012

Fat redistribution following suction lipectomy: defense of body fat and patterns of restoration.

Obesity (Silver Spring) 2011 Jul 7;19(7):1388-95. Epub 2011 Apr 7.

Division of Endocrinology, Metabolism, and Diabetes, Department of Medicine, University of Colorado Denver, Anschutz Medical Campus, Aurora, Colorado, USA.

No randomized studies in humans have examined whether fat returns after removal or where it returns. We undertook a prospective, randomized-controlled trial of suction lipectomy in nonobese women to determine if adipose tissue (AT) is defended and if so, the anatomic pattern of redistribution. Healthy women with disproportionate AT depots (lower abdomen, hips, or thighs) were enrolled. Baseline body composition measurements included dual-energy X-ray absorptiometry (DXA) (a priori primary outcome), abdominal/limb circumferences, subcutaneous skinfold thickness, and magnetic resonance imaging (MRI) (torso/thighs). Participants (n = 32; 36 ± 1 year) were randomized to small-volume liposuction (n = 14, mean BMI: 24 ± 2 kg/m(2)) or control (n=18, mean BMI: 25 ± 2) following baseline. Surgery group participants underwent liposuction within 2-4 weeks. Identical measurements were repeated at 6 weeks, 6 months, and 1 year later. Participants agreed not to make lifestyle changes while enrolled. Between-group differences were adjusted for baseline level of the outcome variable. After 6 weeks, percent body fat (%BF) by DXA was decreased by 2.1% in the lipectomy group and by 0.28% in the control group (adjusted difference (AD): -1.82%; 95% confidence interval (CI): -2.79% to -0.85%; P = 0.0002). This difference was smaller at 6 months, and by 1 year was no longer significant (0.59% (control) vs. -0.41% (lipectomy); AD: -1.00%; CI: -2.65 to 0.64; P = 0.23). AT reaccumulated differently across various sites. After 1 year the thigh region remained reduced (0.77% (control) vs. -1.83% (lipectomy); AD: -2.59%; CI: -3.91 to -1.28; P = 0.0001), but AT reaccumulated in the abdominal region (0.64% (control) vs. 0.42% (lipectomy); AD: -0.22; CI: -2.35 to 1.91; P = 0.84). Following suction lipectomy, BF was restored and redistributed from the thigh to the abdomen.
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http://dx.doi.org/10.1038/oby.2011.64DOI Listing
July 2011

Aspirin for the prevention of cardiovascular events in patients with peripheral artery disease: a meta-analysis of randomized trials.

JAMA 2009 May;301(18):1909-19

Department of Medicine, Division of Cardiovascular Medicine, University of Pennsylvania, Philadelphia, USA.

Context: Randomized trials have shown that aspirin decreases the risk of cardiovascular events in patients with symptomatic coronary and cerebrovascular disease. Despite guideline recommendations for secondary prevention in peripheral artery disease (PAD), the effect of aspirin in this population is not well established.

Objective: To investigate the effect of aspirin on cardiovascular event rates in patients with PAD.

Data Sources And Study Selection: MEDLINE, the Cochrane Central Register of Controlled Trials, EMBASE, Science Citation Index (1966 to December 2008), and unpublished studies from the supplemental index of the Antithrombotic Trialists' Collaboration. Eligible studies were prospective, randomized controlled trials of aspirin therapy, with or without dipyridamole that reported cardiovascular event rates. Eighteen trials involving 5269 individuals were identified.

Data Extraction: Studies were reviewed to determine the number of participants, mean follow-up, and the primary end point of cardiovascular events (nonfatal myocardial infarction [MI], nonfatal stroke, and cardiovascular death). Data on the secondary end points of all-cause mortality, major bleeding, and the individual components of the primary outcome measure were also abstracted. For the primary end point, the analysis had 88% power to detect a 25% reduction and 70% power to detect a 20% reduction in cardiovascular events in the aspirin group compared with the control group.

Data Synthesis: Among 5269 participants, cardiovascular events were experienced by 251 (8.9%) of 2823 patients taking aspirin (alone or with dipyridamole) and by 269 (11.0%) of 2446 in the control group (pooled relative risk [RR], 0.88; 95% confidence interval [CI], 0.76-1.04). Aspirin therapy was associated with a reduction in the secondary outcome of nonfatal stroke (52 of 2823 vs 76 of 2446; RR, 0.66; 95% CI, 0.47-0.94) but was not associated with significant reductions in all-cause or cardiovascular mortality, MI, or major bleeding. In the subset of 3019 participants taking aspirin alone vs control, aspirin was associated with a nonsignificant reduction in cardiovascular events (125 of 1516 vs 144 of 1503; RR, 0.75; 95% CI, 0.48-1.18), a significant reduction in nonfatal stroke (32 of 1516 vs 51 of 1503; RR, 0.64; 95% CI, 0.42-0.99), but no statistically significant reductions in all-cause or cardiovascular mortality, MI, or major bleeding.

Conclusions: In patients with PAD, treatment with aspirin alone or with dipyridamole resulted in a statistically nonsignificant decrease in the primary end point of cardiovascular events and a significant reduction in nonfatal stroke. Results for the primary end point may reflect limited statistical power. Additional randomized controlled trials of aspirin therapy are needed to establish the net benefit and bleeding risks in PAD.
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http://dx.doi.org/10.1001/jama.2009.623DOI Listing
May 2009

Increases in bone mineral density in response to oral dehydroepiandrosterone replacement in older adults appear to be mediated by serum estrogens.

J Clin Endocrinol Metab 2008 Dec 23;93(12):4767-73. Epub 2008 Sep 23.

Division of Geriatric Medicine, University of Colorado Denver, mail stop B179, Room 8111, 12631 East 17th Avenue, Aurora, Colorado 80045, USA.

Context: The mechanisms by which dehydroepiandrosterone (DHEA) replacement increases bone mineral density (BMD) in older adults are not known.

Objective: The aims were to determine the effects of DHEA therapy on changes in sex hormones and IGF-I and their associations with changes in BMD.

Design, Setting, And Participants: A randomized, double-blinded, placebo-controlled trial was conducted at an academic research institution. Participants were 58 women and 61 men, aged 60-88 yr, with low serum DHEA sulfate (DHEAS) levels.

Intervention: The intervention was oral DHEA 50 mg/d or placebo for 12 months.

Main Outcome Measures: BMD and serum DHEAS, testosterone, estradiol (E(2)), estrone (E(1)), SHBG, IGF-I, and IGF binding protein 3 were measured before and after intervention. Free testosterone and estrogen (FEI) indices were calculated.

Results: The average changes in hip and spine BMD (DHEA vs. placebo) ranged from 1.1 to 1.6%. Compared with placebo, DHEA replacement increased serum DHEAS, testosterone, free testosterone index, E(1), E(2), FEI, and IGF-I (all P < 0.001) and decreased SHBG (P = 0.02) in women and, in men, increased DHEAS, E(1), FEI (all P < 0.001), and E(2) (P = 0.02) and decreased SHBG (P = 0.037). The changes in total and regional hip BMD were associated with 12-month E(2) (all P
Conclusions: The significant increases in hip BMD in older adults undergoing DHEA replacement were mediated primarily by increases in serum E(2) rather than direct effects of DHEAS.
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http://dx.doi.org/10.1210/jc.2007-2614DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2626446PMC
December 2008

Frequentist evaluation of group sequential clinical trial designs.

Stat Med 2007 Dec;26(28):5047-80

Department of Biostatistics, Box 357232, University of Washington, Seattle, WA 98195, USA.

Group sequential stopping rules are often used as guidelines in the monitoring of clinical trials in order to address the ethical and efficiency issues inherent in human testing of a new treatment or preventive agent for disease. Such stopping rules have been proposed based on a variety of different criteria, both scientific (e.g. estimates of treatment effect) and statistical (e.g. frequentist type I error, Bayesian posterior probabilities, stochastic curtailment). It is easily shown, however, that a stopping rule based on one of these criteria induces a stopping rule on all other criteria. Thus, the basis used to initially define a stopping rule is relatively unimportant so long as the operating characteristics of the stopping rule are fully investigated. In this paper we describe how the frequentist operating characteristics of a particular stopping rule might be evaluated to ensure that the selected clinical trial design satisfies the constraints imposed by the many different disciplines represented by the clinical trial collaborators.
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http://dx.doi.org/10.1002/sim.2901DOI Listing
December 2007

Bayesian evaluation of group sequential clinical trial designs.

Stat Med 2007 Mar;26(7):1431-49

Department of Biostatistics, Box 357232, University of Washington, Seattle, Washington 98195-7232, USA.

Clinical trial designs often incorporate a sequential stopping rule to serve as a guide in the early termination of a study. When choosing a particular stopping rule, it is most common to examine frequentist operating characteristics such as type I error, statistical power, and precision of confidence intervals (Statist. Med. 2005, in revision). Increasingly, however, clinical trials are designed and analysed in the Bayesian paradigm. In this paper, we describe how the Bayesian operating characteristics of a particular stopping rule might be evaluated and communicated to the scientific community. In particular, we consider a choice of probability models and a family of prior distributions that allows concise presentation of Bayesian properties for a specified sampling plan.
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http://dx.doi.org/10.1002/sim.2640DOI Listing
March 2007

A novel design for estimating relative accuracy of screening tests when complete disease verification is not feasible.

Biometrics 2006 Jun;62(2):605-12

Department of Biostatistics, University of Southern California Keck School of Medicine, 440 E. Huntington Drive, Suite 300, P.O. Box 60012, Arcadia, California 91066, USA.

The accuracy (sensitivity and specificity) of a new screening test can be compared with that of a standard test by applying both tests to a group of subjects in which disease status can be determined by a gold standard (GS) test. However, it is not always feasible to administer a GS test to all study subjects. For example, a study is planned to determine whether a new screening test for cervical cancer ("ThinPrep") is better than the standard test ("Pap"), and in this setting it is not feasible (or ethical) to determine disease status by biopsy in order to identify women with and without disease for participation in a study. When determination of disease status is not possible for all study subjects, the relative accuracy of two screening tests can still be estimated by using a paired screen-positive (PSP) design in which all subjects receive both screening tests, but only have the GS test if one of the screening tests is positive. Unfortunately in the cervical cancer example, the PSP design is also infeasible because it is not technically possible to administer both the ThinPrep and Pap at the same time. In this article, we describe a randomized paired screen-positive (RPSP) design in which subjects are randomized to receive one of the two screening tests initially, and only receive the other screening test and GS if the first screening test is positive. We derive maximum likelihood estimators and confidence intervals for the relative accuracy of the two screening tests, and assess the small sample behavior of these estimators using simulation studies. Sample size formulae are derived and applied to the cervical cancer screening trial example, and the efficiency of the RPSP design is compared with other designs.
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http://dx.doi.org/10.1111/j.1541-0420.2005.00445.xDOI Listing
June 2006

Rheumatoid factor seropositivity is inversely associated with oral contraceptive use in women without rheumatoid arthritis.

Ann Rheum Dis 2007 Feb 25;66(2):267-9. Epub 2006 Jul 25.

Department of Preventive Medicine and Biometrics, University of Colorado at Denver and Health Sciences Center, Denver, 4200 East Ninth Avenue, Box B119, Denver, CO 80262, USA.

Objectives: To examine whether oral contraceptive use is associated with the presence of serum rheumatoid factor in women of reproductive age without rheumatoid arthritis.

Methods: 304 women selected from parents of children who were at increased risk of developing type 1 diabetes were studied, because they were enriched with the human leucocyte antigen-DR4 allele, a susceptibility marker for both type 1 diabetes and rheumatoid arthritis. Participants visited a clinic where blood was drawn for rheumatoid factor testing, and exposure data were collected via questionnaires. A medical history and joint examination were performed to rule out rheumatoid arthritis. Participants and examiners were unaware of the participants' rheumatoid factor status at the time of examination and questionnaire.

Results: Use of oral contraceptives at any time was inversely associated with rheumatoid factor positivity (adjusted odds ratio (OR) 0.2, 95% confidence interval (CI) 0.07 to 0.52) independent of age, education and smoking. Smoking > or = 20 pack-years was also associated with rheumatoid factor positivity (adjusted OR 56.38, 95% CI 4.31 to 736.98) compared with never smoking. Smoking 1-19 pack-years was not associated with a positive rheumatoid factor.

Conclusions: Our results suggest that oral contraceptive use, and possibly cigarette smoking, act early in the development of the immune dysregulation that occurs in rheumatoid arthritis.
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http://dx.doi.org/10.1136/ard.2006.060004DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1798510PMC
February 2007

Effects of dehydroepiandrosterone replacement therapy on bone mineral density in older adults: a randomized, controlled trial.

J Clin Endocrinol Metab 2006 Aug 30;91(8):2986-93. Epub 2006 May 30.

Health Sciences Center, University of Colorado at Denver, 4200 East Ninth Avenue, Campus Box B179, Denver, CO 80262, USA.

Context: Dehydroepiandrosterone (DHEA) and its sulfate (DHEAS) decrease with aging and are important androgen and estrogen precursors in older adults. Declines in DHEAS with aging may contribute to physiological changes that are sex hormone dependent.

Objective: The aim was to determine whether DHEA replacement increases bone mineral density (BMD) and fat-free mass.

Design, Setting, And Participants: A randomized, double-blinded, controlled trial was conducted at an academic research institution. Participants were 70 women and 70 men, aged 60-88 yr, with low serum DHEAS levels.

Intervention: The intervention was oral DHEA 50 mg/d or placebo for 12 months.

Measurements: BMD, fat mass, and fat-free mass were measured before and after intervention.

Results: Intent-to-treat analyses revealed trends for DHEA to increase BMD more than placebo at the total hip (1.0%, P = 0.05), trochanter (1.2%, P = 0.06), and shaft (1.2%, P = 0.05). In women only, DHEA increased lumbar spine BMD (2.2%, P = 0.04; sex-by-treatment interaction, P = 0.05). In secondary compliance analyses, BMD increases in hip regions were significant (1.2-1.6%; all P < 0.02) in the DHEA group. There were no significant effects of DHEA on fat or fat-free mass in intent-to-treat or compliance analyses.

Conclusions: DHEA replacement therapy for 1 yr improved hip BMD in older adults and spine BMD in older women. Because there have been few randomized, controlled trials of the effects of DHEA therapy, these findings support the need for further investigations of the benefits and risks of DHEA replacement and the mechanisms for its actions.
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http://dx.doi.org/10.1210/jc.2005-2484DOI Listing
August 2006

Group sequential clinical trials for longitudinal data with analyses using summary statistics.

Stat Med 2005 Aug;24(16):2457-75

Department of Preventive Medicine and Biometrics, University of Colorado Health Sciences Center, Denver, 80262, USA.

Longitudinal endpoints are used in clinical trials, and the analysis of the results is often conducted using within-individual summary statistics. When these trials are monitored, interim analyses that include subjects with incomplete follow-up can give incorrect decisions due to bias by non-linearity in the true time trajectory of the treatment effect. Linear mixed-effects models can be used to remove this bias, but there is a lack of software to support both the design and implementation of monitoring plans in this setting. This paper considers a clinical trial in which the measurement time schedule is fixed (at least for pre-trial design), and the scientific question is parameterized by a contrast across these measurement times. This setting assures generalizable inference in the presence of non-linear time trajectories. The distribution of the treatment effect estimate at the interim analyses using the longitudinal outcome measurements is given, and software to calculate the amount of information at each interim analysis is provided. The interim information specifies the analysis timing thereby allowing standard group sequential design software packages to be used for trials with longitudinal outcomes. The practical issues with implementation of these designs are described; in particular, methods are presented for consistent estimation of treatment effects at the interim analyses when outcomes are not measured according to the pre-trial schedule. Splus/R functions implementing this inference using appropriate linear mixed-effects models are provided. These designs are illustrated using a clinical trial of statin treatment for the symptoms of peripheral arterial disease.
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http://dx.doi.org/10.1002/sim.2127DOI Listing
August 2005

Gender differences in lipoprotein lipase activity after acute exercise.

Obes Res 2004 Feb;12(2):241-9

Department of Medicine, Division of Endocrinology, Metabolism and Diabetes, University of Colorado Health Sciences Center, Denver, Colorado 80262, USA.

Objective: To determine whether gender differences exist in lipoprotein lipase (LPL) activity in response to exercise and/or insulin. Exercise and insulin are known modulators of LPL activity in men, but this is less clear in women. LPL activity may predict propensity for obesity; therefore, understanding its modulators is of considerable importance.

Research Methods And Procedures: Gender differences in skeletal muscle and adipose tissue LPL activity were determined after a single bout of exercise followed by a hyperinsulinemic/euglycemic clamp and compared with an identical rest day in healthy lean men (n = 10) and women (n = 10). Muscle and adipose tissue biopsies were obtained pre- (post-exercise vs. rest) and post-clamp.

Results: Basal levels of muscle and adipose tissue LPL activity were not different between men and women. There was, however, a significant gender by day interaction for muscle LPL activity (p = 0.023) and adipose tissue LPL activity (p = 0.013). In muscle, this was because of a significant increase in LPL activity on the exercise vs. rest day in men (p < 0.001) but not women. Adipose tissue LPL activity also increased significantly in men on the exercise day relative to rest day (p = 0.04) but decreased in women (p = 0.10). The hyperinulinemic/euglycemic clamp had no independent effect on tissue LPL activity, in either gender, after rest or exercise.

Discussion: In the 3 to 4 hours after exercise, muscle and adipose tissue LPL activity increased significantly in men, whereas LPL activity remained unchanged in women.
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http://dx.doi.org/10.1038/oby.2004.31DOI Listing
February 2004

Prognostic importance of tumor size for localized conventional (clear cell) renal cell carcinoma: assessment of TNM T1 and T2 tumor categories and comparison with other prognostic parameters.

Cancer 2002 Feb;94(3):658-64

Department of Pathology, Wellington School of Medicine, University of Otago, Wellington, New Zealand.

Background: The T1 and T2 classifications of the International Union Against Cancer TNM classification system for renal cell carcinoma are based on primary tumor size, and in various editions of the classification, the cut points between T1 and T2 have been amended to provide clinical utility. In the current edition, the T1/T2 cut point is less than or equal to and greater than 7 cm. and more recently a subdivision of the T1 classification (less than or equal to and < 4 cm) has been proposed to identify patients suitable for partial nephrectomy. This study investigates the prognostic significance of tumor size in a series of organ-confined clear cell renal cell carcinomas.

Methods: One hundred thirty cases of organ-confined clear cell renal cell carcinomas, with a minimum of 5 years' follow-up, were identified from the New South Wales Cancer Registry. Tumor size was compared with survival using the method of Kaplan and Meier for TNM size categories, and proportional hazards regression was used for assessing size as a continuous variable. Proportional hazards regression also was used for multivariable comparisons of size and other prognostic parameters (Fuhrman grade, AgNOR score, and Ki-67 index) against survival.

Results: Of 116 cases for which tumor dimension was recorded, 25 patients had died of cancer-related causes. Primary tumor size ranged from 12 to 140 mm (mean, 57.3 mm). The association between survival and size was significant irrespective of the TNM classification and was also significant when size was modeled continuously (P = 0.000125, hazard of death increased by 3.51 times for each doubling of tumor size). On univariate analysis, Fuhrman grade (P = 0.04) and AgNOR score (P = 0.015) were associated with survival; however, on multivariate analysis only tumor size retained significance.

Conclusions: Although the cut point of T1 and T2 TNM categories and the proposed T1 subdivision cut point correlate with survival, our finding that size is a continuous variable indicates that as a prognostic parameter for clear cell renal cell carcinoma, primary tumor size is relative rather than indicative.
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http://dx.doi.org/10.1002/cncr.10255DOI Listing
February 2002
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