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A post hoc evaluation of a sample size re-estimation in the Secondary Prevention of Small Subcortical Strokes study.

ABSTRACT: The use of adaptive designs has been increasing in randomized clinical trials. Sample size re-estimation is a type of adaptation in which nuisance parameters are estimated at an interim point in the trial and the sample size re-computed based on these estimates. The Secondary Prevention of Small Subcortical Strokes study was a randomized clinical trial assessing the impact of single- versus dual-antiplatelet therapy and control of systolic blood pressure to a higher (130-149?mmHg) versus lower (<130?mmHg) target on recurrent stroke risk in a two-by-two factorial design. A sample size re-estimation was performed during the Secondary Prevention of Small Subcortical Strokes study resulting in an increase from the planned sample size of 2500-3020, and we sought to determine the impact of the sample size re-estimation on the study results.We assessed the results of the primary efficacy and safety analyses with the full 3020 patients and compared them to the results that would have been observed had randomization ended with 2500 patients. The primary efficacy outcome considered was recurrent stroke, and the primary safety outcomes were major bleeds and death. We computed incidence rates for the efficacy and safety outcomes and used Cox proportional hazards models to examine the hazard ratios for each of the two treatment interventions (i.e. the antiplatelet and blood pressure interventions).In the antiplatelet intervention, the hazard ratio was not materially modified by increasing the sample size, nor did the conclusions regarding the efficacy of mono versus dual-therapy change: there was no difference in the effect of dual- versus monotherapy on the risk of recurrent stroke hazard ratios (n?=?3020 HR (95% confidence interval): 0.92 (0.72, 1.2), p?=?0.48; n?=?2500 HR (95% confidence interval): 1.0 (0.78, 1.3), p?=?0.85). With respect to the blood pressure intervention, increasing the sample size resulted in less certainty in the results, as the hazard ratio for higher versus lower systolic blood pressure target approached, but did not achieve, statistical significance with the larger sample (n?=?3020 HR (95% confidence interval): 0.81 (0.63, 1.0), p?=?0.089; n?=?2500 HR (95% confidence interval): 0.89 (0.68, 1.17), p?=?0.40). The results from the safety analyses were similar to 3020 and 2500 patients for both study interventions. Other trial-related factors, such as contracts, finances, and study management, were impacted as well.Adaptive designs can have benefits in randomized clinical trials, but do not always result in significant findings. The impact of adaptive designs should be measured in terms of both trial results, as well as practical issues related to trial management. More post hoc analyses of study adaptations will lead to better understanding of the balance between the benefits and the costs.

SUBMITTER: McClure LA

PROVIDER: S-EPMC5025324 | biostudies-literature | 2016 Oct

REPOSITORIES: biostudies-literature

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A post hoc evaluation of a sample size re-estimation in the Secondary Prevention of Small Subcortical Strokes study.

McClure Leslie A LA Szychowski Jeff M JM Benavente Oscar O Hart Robert G RG Coffey Christopher S CS

Clinical trials (London, England) 20160419 5

<h4>Background/aims</h4>The use of adaptive designs has been increasing in randomized clinical trials. Sample size re-estimation is a type of adaptation in which nuisance parameters are estimated at an interim point in the trial and the sample size re-computed based on these estimates. The Secondary Prevention of Small Subcortical Strokes study was a randomized clinical trial assessing the impact of single- versus dual-antiplatelet therapy and control of systolic blood pressure to a higher (130- ...[more]

PMID: 27094488

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Project description:BackgroundThe effect of intensive blood pressure (BP) lowering on kidney function among individuals with established cerebrovascular disease and preserved estimated glomerular filtration rate (eGFR) is not established.Methods and resultsAmong 2610 participants randomized to a lower (<130 mm Hg) versus higher (130-149 mm Hg) systolic BP target with repeated measures of serum creatinine, we evaluated differences by study arm in annualized eGFR decline and rapid decline (eGFR decline >30%) using linear mixed models and logistic regression, respectively. We assessed associations of both treatment and kidney function decline with stroke, major vascular events, and the composite of stroke, death, major vascular events, or myocardial infarction using multivariable Cox regression, separately and jointly including a test for interaction. Analyses were conducted by treatment arm. Mean age was 63±11 years; 949 participants (36%) were diabetic; and mean eGFR was 80±19 mL·min(-1)·1.73 m(-2). At 9 months, achieved systolic BP was 137±15 versus 127±14 mm Hg in the higher versus lower BP group, and differences were maintained throughout follow-up (mean, 3.2 years). Compared with the higher target, the lower BP target had a -0.50-mL·min(-1)·1.73 m(-2) per year (95% confidence interval [CI], -0.79 to -0.21) faster eGFR decline. Differences were most pronounced during the first year (-2.1 mL·min(-1)·1.73 m(-2); 95% CI, -0.97 to -3.2), whereas rates of eGFR decline did not differ after year 1 (-0.095; 95% CI, -0.47 to 0.23). A total of 313 patients (24%) in the lower BP group had rapid kidney function decline compared with 247 (19%) in the higher BP group (odds ratio, 1.4; 95% CI, 1.1-1.6). Differences in rapid decline by treatment arm were apparent in the first year (odds ratio, 1.4; 95% CI, 1.1-1.8) but were not significant after year 1 (odds ratio, 1.0; 95% CI, 0.73-1.4). Rapid decline was associated with higher risk for stroke, major vascular events, and composite after full adjustment among individuals randomized to the higher BP target (stroke hazard ratio, 1.93; 95% CI, 1.15-3.21) but not the lower BP arm (stroke hazard ratio, 0.93; 95% CI, 0.50-1.75; all P for interaction <0.06).ConclusionsIn patients with prior lacunar stroke and relatively preserved kidney function, intensive BP lowering was associated with a greater likelihood of rapid kidney function decline. Differences were observed primarily during the first year of antihypertensive treatment. Rapid kidney function decline was not associated with increased risk for clinical events among those undergoing intensive BP lowering.Clinical trial registrationURL: http://www.clinicalTrials.gov. Unique identifier: NCT00059306.

Project description:The role of the CYP2C19 genotype on clopidogrel efficacy has been studied widely, with data suggesting reduced clopidogrel efficacy in loss-of-function variant carriers taking clopidogrel after percutaneous coronary intervention; however, data are limited regarding the association between CYP2C19 genetic variants and outcomes in stroke patients. We investigated whether CYP2C19 metabolizer status affects the risk of recurrent stroke or major bleeding in subcortical stroke patients taking dual antiplatelet therapy with aspirin and clopidogrel.CYP2C19*2 and CYP2C19*17 were genotyped in 522 patients treated with dual antiplatelet therapy from the Secondary Prevention of Small Subcortical Strokes (SPS3) study. CYP2C19 metabolizer status was inferred from genotype, and associations with the risk of recurrent stroke and major bleeding were assessed in the overall cohort and by race/ethnic group with logistic regression modeling. In the overall cohort, there were no differences in outcomes by CYP2C19 metabolizer status (recurrent stroke, odds ratio 1.81 [95% CI 0.76 to 4.30]; major bleeding, odds ratio 0.67 [95% CI 0.22 to 2.03]). In white participants, those with CYP2C19 intermediate or poor metabolizer status had higher odds of recurrent stroke (odds ratio 5.19 [95% CI 1.08 to 24.90]) than those with extensive or ultrarapid metabolizer status, but there was no evidence of difference in major bleeding.There were significant differences in recurrent stroke by CYP2C19 genotype-inferred metabolizer status in white subcortical stroke patients receiving dual antiplatelet therapy with aspirin and clopidogrel, consistent with cardiovascular studies on CYP2C19 and clopidogrel; however, the bleeding risk that led to early termination of the antiplatelet arm of the SPS3 trial does not appear to be explained by CYP2C19 genotype. This study was relatively underpowered; therefore, these findings should be interpreted with caution and warrant replication.URL: www.clinicaltrials.gov. Unique identifier: NCT00059306.

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A post hoc evaluation of a sample size re-estimation in the Secondary Prevention of Small Subcortical Strokes study.

Publications

A post hoc evaluation of a sample size re-estimation in the Secondary Prevention of Small Subcortical Strokes study.

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