Biomedical subjects

Alex Dmitrienko

Publications and source records attributed to Alex Dmitrienko.

6 recordsLinked to original sources

PubMed2007

Tree-structured gatekeeping tests in clinical trials with hierarchically ordered multiple objectives.

This paper discusses a new class of multiple testing procedures, tree-structured gatekeeping procedures, with clinical trial applications. These procedures arise in clinical trials with hierarchically ordered multiple objectives, for example, in the context of multiple dose-control tests with logical restrictions or analysis of multiple endpoints. The proposed approach is based on the principle of closed testing and generalizes the serial and parallel gatekeeping approaches developed by Westfall and Krishen (J. Statist. Planning Infer. 2001; 99:25-41) and Dmitrienko et al. (Statist. Med. 2003; 22:2387-2400). The proposed testing methodology is illustrated using a clinical trial with multiple endpoints (primary, secondary and tertiary) and multiple objectives (superiority and non-inferiority testing) as well as a dose-finding trial with multiple endpoints.

Antihypertensive Agents↗

PubMed2007

Challenge of multiple co-primary endpoints: a new approach.

There are many disorders where regulatory agencies have required a new treatment to demonstrate efficacy on multiple co-primary endpoints, all significant at the one-sided 2.5 per cent level, before accepting the treatment's effect for the disorder. This requirement, rooted in the intersection-union (IU) test, has led many researchers to increase the study sample size to make up for the reduction in the statistical power at the study level. Unfortunately, the increase in sample size could be substantial when the endpoints are minimally correlated and the treatment effects on the multiple endpoints are comparable. In this paper, we demonstrate that the frequentist concept of controlling the maximum false positive rate, even when applied to a restricted null space, has only limited success in keeping the sample size increase at a reasonable level. We therefore propose an approach that is based on the notion of controlling an average type I error rate. By employing an upper bound for the average type I error rate, the new approach provides an adjustment to the significance level that depends only on the correlation among the endpoints. For the most common case of two or three co-primary endpoints, the adjusted significance level is at most 5 per cent (one-sided) when the endpoints are moderately correlated. We show how sample size could be calculated under the proposed approach and contrast the needed sample size with that required under the IU test. We provide additional comments and discuss why the new approach is consistent with the principle requiring evidence of significance in the drug development and approval process.

Algorithms↗

PubMed2006

Fallback tests in dose-response clinical trials.

This article introduces a general testing procedure for performing dose-control comparisons in dose-response trials with one or more endpoints. The procedure (termed multi-stage fallback procedure) is an extension of the fallback test proposed by Wiens (2003). The multi-stage fallback procedure features a simple stepwise form and improves the power of dose-control tests at higher doses by taking into account the ordering of the doses. It also serves as an efficient tool for handling multiplicity caused by multiple endpoints. It is shown in this article that the multi-stage fallback procedure can be formulated as a closed testing procedure and thus controls the Type I error rate with respect to multiple dose-control comparisons as well as multiple endpoints. The proposed testing method is illustrated using examples from dose-response clinical trials with single and multiple endpoints.

Algorithms↗

PubMed2005

LY315920NA/S-5920, a selective inhibitor of group IIA secretory phospholipase A2, fails to improve clinical outcome for patients with severe sepsis.

OBJECTIVE: Group IIA secretory phospholipase A2 (sPLA2-IIA), released during inflammation, is increased in severe sepsis, and plasma levels are inversely related to survival. In a previous study, a selective inhibitor of sPLA2-IIA (LY315920NA/S-5920) was well tolerated and appeared to improve survival in a subgroup of patients who received the drug within 24 hrs of first sepsis-induced organ failure. This study was designed to determine whether improvement in survival could be confirmed in a larger patient population meeting the characteristics of that subgroup. DESIGN: Multicenter, double-blind, placebo-controlled, parallel-group clinical trial of LY315920NA/S-5920 in patients with severe sepsis. SETTING: Seventy-five institutions worldwide. PATIENTS: A total of 373 patients with at least two sepsis-induced organ failures. INTERVENTIONS: Patients were randomized 1:1 to receive LY315920NA/S-5920 (target plasma concentration of 800 ng/mL; n = 188) or placebo (n = 185). Study medication was administered as a continuous intravenous infusion for 168 hrs. MEASUREMENTS AND MAIN RESULTS: The study was terminated after data on 250 patients suggested a significant improvement in 28-day all-cause mortality would not be found if the trial continued as planned. The mortality rate was 39.4% in the LY315920NA/S-5920 group, compared with 31.9% in the placebo group (p = .092). The negative trend in mortality was most pronounced among patients with cardiovascular failure at baseline (41.6% vs. 28.7%; p = .008) and patients whose culture data at baseline were negative (42.9% vs. 22.7%; p = .045). The negative trend in mortality is not explained by adverse events, microbiology, or laboratory data. CONCLUSIONS: Continuous 7-day infusion of an inhibitor of sPLA2-IIA had no beneficial effect on 28-day all-cause mortality among severe sepsis patients with at least two organ failures. This study did not confirm earlier promising subgroup results with LY315920NA/S-5920, which provides a reminder that subgroup effects should be viewed cautiously, especially when primary effects are not significant.

Acetates↗

PubMed2003

Covariate-adjusted reference intervals for diagnostic data.

The analysis of extreme diagnostic measurements in clinical trials relies on reference intervals that help drug developers quickly determine whether a particular value is typical or atypical. The distribution of diagnostic variables is often greatly influenced by various covariates and it is important to properly account for this influence in the analysis of extreme measurements. This paper discusses three approaches to constructing covariate-adjusted reference intervals for quantitative diagnostic data: global quantile smoothing, local quantile smoothing, and stepwise quantile approximations based on recursive partitioning. A detailed review of methods for optimizing the quantile estimation procedures is provided. The paper presents algorithms for selecting the degree of a polynomial approximation in global smoothing, bandwidth parameter in local smoothing, and number of strata in recursive partitioning. The described methods for computing covariate-adjusted reference intervals are applied to the analysis of electrocardiographic data.

Adolescent↗

PubMed2003

Efficacy and safety of LY315920Na/S-5920, a selective inhibitor of 14-kDa group IIA secretory phospholipase A2, in patients with suspected sepsis and organ failure.

OBJECTIVE: Concentrations of group IIA secretory phospholipase A, an inflammatory response mediator, are increased in the plasma of patients with sepsis and septic shock, and the extent of elevation is correlated with mortality. LY315920Na/S-5920 is a selective inhibitor of group IIA secretory phospholipase A that has been shown to inhibit serum group IIA secretory phospholipase A enzyme activity in patients with severe sepsis. The primary objectives of this study were to determine whether there was a dose-response relationship between two doses of LY315920Na/S-5920 compared with placebo in the reduction of 28-day all-cause mortality in patients with severe sepsis and to determine whether LY315920Na/S-5920 had an acceptable safety profile.(2) (2) (2) DESIGN: Multicenter, double-blind, placebo-controlled trial of two doses of LY315920Na/S-5920 in a parallel design. PATIENTS: A total of 586 patients with severe sepsis at 72 institutions in the United States. INTERVENTIONS Patients enrolled within 72 hrs from onset of first sepsis-induced organ failure were randomized (1:1:1) to low-dose LY315920Na/S-5920 (target plasma concentration of 200 ng/mL, n = 196), high-dose LY315920Na/S-5920 (800 ng/mL, n = 194), or placebo (n = 196). Study medication was administered as a constant-rate intravenous infusion for 168 hrs. MEASUREMENTS AND MAIN RESULTS: The study was stopped prematurely because it was unlikely that a statistically significant difference in mortality between LY315920Na/S-5920 and placebo would be found. There was no effect of LY315920Na/S-5920 on the primary end point of 28-day all-cause mortality across the entire study population. The 28-day all-cause mortality was distributed as follows: placebo group, 33.2% (65/196 patients); low-dose LY315920Na/S-5920, 37.2% (73/196); and high-dose LY315920Na/S-5920, 36.1% (70/194); p = .525. However, in a prospectively planned analysis, there was a favorable overall dose-response effect on 28-day all-cause mortality in patients administered LY315920Na/S-5920 within 18 hrs of onset of the first sepsis-induced organ failure. Among these patients, 28-day all-cause mortality was distributed as follows: placebo group, 43.5% (20/46 patients); low-dose LY315920Na/S-5920, 31.4% (16/51); and high-dose LY315920Na/S-5920, 20.8% (10/48); p = .018. CONCLUSIONS: Administration of LY315920Na/S-5920 had an acceptable safety profile in patients with severe sepsis. There was no overall survival benefit associated with the use of LY315920Na/S-5920 in this study. However, prospectively planned secondary analyses suggested that treatment with LY315920Na/S-5920 was associated with an improvement in survival in patients treated within 18 hrs of the first sepsis-induced organ failure.

Acetates↗