Biomedical subjects

Meinhard Kieser

Publications and source records attributed to Meinhard Kieser.

10 recordsLinked to original sources

PubMed2007

Planning and analysis of three-arm non-inferiority trials with binary endpoints.

Three-arm trials including an experimental treatment, an active control and a placebo group are frequently preferred for the assessment of non-inferiority. In contrast to two-arm non-inferiority studies, these designs allow a direct proof of efficacy of a new treatment by comparison with placebo. As a further advantage, the test problem for establishing non-inferiority can be formulated in such a way that rejection of the null hypothesis assures that a pre-defined portion of the (unknown) effect the reference shows versus placebo is preserved by the treatment under investigation. We present statistical methods for this study design and the situation of a binary outcome variable. Asymptotic test procedures are given and their actual type I error rates are calculated. Approximate sample size formulae are derived and their accuracy is discussed. Furthermore, the question of optimal allocation of the total sample size is considered. Power properties of the testing strategy including a pre-test for assay sensitivity are presented. The derived methods are illustrated by application to a clinical trial in depression.

Controlled Clinical Trials as Topic↗

PubMed2006

Hamamelis in children with skin disorders and skin injuries: results of an observational study.

Published clinical experience with hamamelis ointment in children is limited. This observational study included children (age 27 days to 11 years) with minor skin injuries, diaper dermatitis, or localized inflammation of skin. The children received either hamamelis ointment or dexpanthenol ointment in groups at a 3-to-1 ratio. Baseline and post-treatment assessments compared the total scores of predefined signs and symptoms for each condition. Physicians and parents were asked for a global assessment of efficacy and tolerability of the respective treatments at the end of therapy. A total of 309 children were treated (hamamelis n = 231; dexpanthenol n = 78). The treatment groups were comparable regarding demographic data and baseline total scores of signs and symptoms. In all three diagnosis groups, the efficacy of hamamelis and dexpanthenol was shown by a statistically significant and clinically relevant decrease of total scores from baseline to endpoint (p < 0.0001 for each group, Wilcoxon signed-rank test). Overall, the results for the hamamelis and the dexpanthenol groups were similar. Descriptive advantages for the hamamelis group were observed for a number of parameters and diagnosis groups. Both treatments were well tolerated. Ratings of the tolerability of hamamelis were "excellent" or "good" in 99.1% (physicians) and 98.2% (parents) of cases, respectively. The corresponding ratings for dexpanthenol were 97.4 and 92.3%. In conclusion, hamamelis ointment is an effective and safe treatment for certain skin disorders in children up to the age of 11 years. The observed effects are similar to dexpanthenol.

Anti-Inflammatory Agents↗

PubMed2006

Superior efficacy of St John's wort extract WS 5570 compared to placebo in patients with major depression: a randomized, double-blind, placebo-controlled, multi-center trial [ISRCTN77277298].

BACKGROUND: The aim of the current study was to assess the antidepressant efficacy and safety of Hypericum perforatum (St. John's wort) extract WS 5570 at doses of 600 mg/day in a single dose and 1200 mg/day in two doses. METHODS: The participants in this double-blind, randomized, placebo-controlled, multi-center clinical trial were male and female adult out-patients with an episode of mild or moderate major depressive episode (single or recurrent episode, DSM-IV criteria). As specified by the relevant guideline, the study was preceded by a medication-free run-in phase. For the 6-week treatment, 332 patients were randomized: 123 to WS 5570 600 mg/day, 127 to WS 5570 1200 mg/day, and 82 to placebo. The primary outcome measure was the change in total score on the Hamilton Rating Scale for Depression (HAM-D, 17-item version) between baseline and endpoint. Additional measures included the number of responders, the number of patients in remission, and several other standard rating scales. Efficacy and safety were assessed after 2 and 6 weeks. The design included an interim analysis performed after randomization with the option of early termination. RESULTS: After 6 weeks of treatment, mean +/- standard deviation decreases in HAM-D total scores of 11.6 +/- 6.4, 10.8 +/- 7.3, and 6.0 +/- 8.1 points were observed for the WS 5570 600 mg/day, 1200 mg/day and placebo groups, respectively (endpoint analysis). Secondary measures of treatment efficacy also showed that both WS 5570 groups were statistically superior to placebo. Significantly more patients in the WS 5570 treatment groups than in the placebo group showed treatment response and remission. WS 5570 was consistently more effective than placebo in patients with either less severe or more severe baseline impairment. The number of patients who experienced remission was higher in the WS 5570 1200 mg/day group than the WS 5570 600 mg/day group. The incidence of adverse events was low in all groups. The adverse event profile was consistent with the known profile for Hypericum extract preparations. CONCLUSION: Hypericum perforatum extract WS 5570 at doses of 600 mg/day (once daily) and 1200 mg/day (600 mg twice daily) were found to be safe and more effective than placebo, with comparable efficacy of the WS 5570 groups for the treatment of mild to moderate major depression.

Adolescent↗

PubMed2006

Sample size recalculation in internal pilot study designs: a review.

The adequacy of sample size is important to clinical trials. In the planning phase of a trial, however, the investigators are often quite uncertain about the sizes of parameters which are needed for sample size calculations. A solution to this problem is mid-course recalculation of the sample size during the ongoing trial. In internal pilot study designs, nuisance parameters are estimated on the basis of interim data and the sample size is adjusted accordingly. This review attempts to give an overview on the available methods. It is written not only for biometricians who are already familar with the the topic and wish to update their knowledge but also for users new to the subject.

Clinical Trials as Topic↗

PubMed2005

A randomized, double-blind, placebo-controlled trial of two doses of Ginkgo biloba extract in dementia of the Alzheimer's type.

CONTEXT: Previous studies of Ginkgo biloba extract (GbE) in patients with various forms of cognitive impairment or dementia have shown promising results. OBJECTIVE: To determine the clinical efficacy of GbE in mild to moderate dementia of the Alzheimer type. DESIGN: Randomized, placebo-controlled, double-blind, parallel-group, multicenter trial. SETTING: Outpatient clinics of universities and private research centers specialized in dementia. PATIENTS: 513 outpatients with uncomplicated dementia of the Alzheimer's type scoring 10 to 24 on the Mini-Mental State Examination and less than 4 on the modified Hachinski Ischemic Score, free of other serious illnesses and not requiring continuous treatment with any psychoactive drug. INTERVENTION: 26-week treatment with GbE at daily doses of 120 mg or 240 mg or placebo. MAIN OUTCOMES: Cognitive subscale of the Alzheimer's Disease Assessment Scale (ADAS-cog), Alzheimer's Disease Cooperative Study Clinical Global Impression of Change (ADCS-CGIC). RESULTS: There were no significant between-group differences for the whole sample. There was little cognitive and functional decline of the placebo-treated patients, however. For a subgroup of patients with neuropsychiatric symptoms there was a greater decline of placebo-treated patients and significantly better cognitive performance and global assessment scores for the patients on GbE. CONCLUSION: The trial did not show efficacy of GbE, however, the lack of decline of the placebo patients may have compromised the sensitivity of the trial to detect a treatment effect. Thus, the study remains inconclusive with respect to the efficacy of GbE.

Aged↗

PubMed2004

Power and sample size determination when assessing the clinical relevance of trial results by 'responder analyses'.

A fundamental issue in regulatory decision making is the assessment of the benefit/risk profile of a compound. In order to do this, establishing the existence of a treatment effect by a significance test is not sufficient, but the clinical relevance of a potential benefit must also be taken into account. A number of regulatory guidelines propose that clinical relevance should be assessed by considering the rate of responders, i.e. the proportion of patients who are observed to achieve an apparently meaningful benefit. In this paper, we present methods for planning clinical trials that aim at demonstrating both statistical and clinical significance in superiority trials. Procedures based on analytical calculations are derived for normally distributed data and the case of a single endpoint as well as multiple primary outcomes. A bootstrap procedure is proposed that can be applied to non-normal data. Application is illustrated by a clinical trial in Alzheimer's disease.

Activities of Daily Living↗

PubMed2004

Influence of a 7-day treatment with Ginkgo biloba special extract EGb 761 on bleeding time and coagulation: a randomized, placebo-controlled, double-blind study in healthy volunteers.

During recent years, several case reports have been published in which the authors have voiced their suspicion of a causal relationship between hemorrhagic complications and the intake of Ginkgo biloba preparations. Therefore, a trial was conducted to investigate the influence of Ginkgo biloba special extract EGb 761 on hemostasiological parameters. Fifty healthy, male volunteers underwent 7 days of crossover treatment with 2 x 120 mg/day EGb 761 and placebo in randomized sequence. Between the two treatment phases, a washout-period of at least 3 weeks was inserted. The study's main outcome measures were bleeding time, coagulation parameters, platelet activity in response to various agonists and platelet morphology. The equivalence of the two treatments was analyzed by computing the 90% Fieller confidence intervals for the ratio between the means of the pre-post treatment differences for EGb 761 and placebo, respectively. Treatment safety was investigated by clinical laboratory and vital signs assessment and by adverse events monitoring. Among the 29 coagulation and bleeding parameters assessed, none showed any evidence of an inhibition of blood coagulation and platelet aggregation through EGb 761. Furthermore, the study did not reveal any evidence to substantiate a causal relationship between the administration of EGb 761 and hemorrhagic complications. As regards treatment tolerability, there were no interpretable differences between EGb 761 and placebo except for a slight increase of gastrointestinal complaints during administration of the herbal extract.

Adult↗

PubMed2003

Simple procedures for blinded sample size adjustment that do not affect the type I error rate.

For normally distributed data, determination of the appropriate sample size requires a knowledge of the variance. Because of the uncertainty in the planning phase, two-stage procedures are attractive where the variance is reestimated from a subsample and the sample size is adjusted if necessary. From a regulatory viewpoint, preserving blindness and maintaining the ability to calculate or control the type I error rate are essential. Recently, a number of proposals have been made for sample size adjustment procedures in the t-test situation. Unfortunately, none of these methods satisfy both these requirements. We show through analytical computations that the type I error rate of the t-test is not affected if simple blind variance estimators are used for sample size recalculation. Furthermore, the results for the expected power of the procedures demonstrate that the methods are effective in ensuring the desired power even under initial misspecification of the variance. A method is discussed that can be applied in a more general setting and that assumes analysis with a permutation test. This procedure maintains the significance level for any design situation and arbitrary blind sample size recalculation strategy.

Anxiety Disorders↗

PubMed2003

Blinded sample size reassessment in non-inferiority and equivalence trials.

Even in situations where the design and conduct of clinical trials is highly standardized, there may be a considerable between-study variation in the observed variability of the primary outcome variable. As a consequence, performing a study in a fixed sample size design implies a considerable risk of resulting in a too high or too low sample size. This difficulty can be alleviated by applying a design with internal pilot study. After a provisional sample size calculation in the planning stage, a portion of the planned sample is recruited and the sample size is recalculated on the basis of the observed variability. To comply with the requirement of some regulatory guidelines only blinded data should be used for the reassessment procedure. Furthermore, the effect on the type I error rate should be quantified. The current literature presents analytical results on the actual level in the t-test situation only for superiority trials. In these situations, blinded sample size recalculation does not lead to an inflation of the type I error rate. We extended the methodology to non-inferiority and equivalence trials with normally distributed outcome variable and hypotheses formulated in terms of the ratio and difference of means. Surprisingly, in contrast to the case of testing superiority, we observed actual type I error rates above the nominal level. The extent of inflation depends on the required sample size, the sample size of the internal pilot study, and the standardized equivalence or non-inferiority margin. It turned out that the elevation of the significance level is negligible for most practical situations. Nevertheless, the consequences of sample size reassessment have to be discussed case by case and regulatory concerns with respect to the actual size of the procedure cannot generally be refuted by referring to the fact that only blinded data were used.

Asthma↗

PubMed2002

On the inappropriateness of an EM algorithm based procedure for blinded sample size re-estimation.

When planning a clinical trial the sample size calculation is commonly based on an a priori estimate of the variance of the outcome variable. Misspecification of the variance can have substantial impact on the power of the trial. It is therefore attractive to update the planning assumptions during the ongoing trial using an internal estimate of the variance. For this purpose, an EM algorithm based procedure for blinded variance estimation was proposed for normally distributed data. Various simulation studies suggest a number of appealing properties of this procedure. In contrast, we show that (i) the estimates provided by this procedure depend on the initialization, (ii) the stopping rule used is inadequate to guarantee that the algorithm converges against the maximum likelihood estimator, and (iii) the procedure corresponds to the special case of simple randomization which, however, in clinical trials is rarely applied. Further, we show that maximum likelihood estimation leads to no reasonable results for blinded sample size re-estimation due to bias and high variability. The problem is illustrated by a clinical trial in asthma.

Administration, Inhalation↗