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with a clustered randomized design require a sample size almost seven times as large as that of the clinical trials using the traditional individual randomization. Two commonly encountered mistakes in most cluster randomized trials are given below 1. Although the trials adopt a cluster randomization, the analysis of data completely ignores this fact and uses subject as the unit of analysis. 2. Sample size estimation fails to take into consideration the variance inflation factor. The first...
Combination Trials
As was indicated in Chapter 1, a treatment is defined as a combination therapy if it consists of more than one active ingredient. A treatment is called a combined product if it is a combination of different pharmaceutical entities such as drugs, biologics, and or medical devices. Since the general principles of statistical designs and analyses for the assessment of the effectiveness and safety are the same for both combination therapy and combined product, in this section our discussion will be...
Goals Of Clinical Trials
The ultimate goal of clinical research is to obtain an unbiased inference with possibly best precision in order to scientifically address the clinical questions regarding the study drug under investigation with respect to a target patient population. As indicated by Lachin 2000 , the meaning of an unbiased trial is two-fold. First, the estimated treatment effect between the investigational drug and a control is unbiased. Second, the statistical testing procedure for detecting a treatment effect...
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It follows that the two-tailed p-value for the Fisher's exact test is the sum of probabilities over a set of tables with P Y11 less than or equal to the probability calculated from the observed frequency y11. Note that the only requirement for the assumption of a hypergeometric distribution in 9.3.16 and the expected frequency of Y11 in 9.3.13 is randomization of subjects to receive either the test drug or the placebo. As a result the variance of Y11 derived from hypergeometric distribution is...
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Figure 2.6.3 Sampling distribution of one-sided test. Figure 2.6.3 Sampling distribution of one-sided test. Then the level of proof required should be squared regardless of which test is used. Table 2.6.2 summarizes the levels of proof required for the marketing approval of a drug product. As Table 2.6.2 indicates, the levels of proof required for one-sided and two-sided tests are one out of 400 and one out of 1600, respectively. Fisher 1991 argues that the level of proof of one out of 400 is a...
Parallel Group Designs
A parallel group design is a complete randomized design in which each patient receives one and only one treatment in a random fashion. Basically there are two types of parallel group design for comparative clinical trials, namely, group comparison or parallel-group designs and matched pairs parallel designs. The simplest group comparison parallel group design is the two-group parallel design which compares two treatments e.g., a treatment group vs. a control group . Each treatment group...
Bias And Variability
As was indicated earlier, the FDA requires that the results from clinical trials be accurate and reliable in order to provide a valid and unbiased assessment of true efficacy and safety of the study medication. The accuracy and reliability are usually referred to as the closeness and the degree of the closeness of the clinical results to the true value regarding the targeted patient population. The accuracy and reliability can be assessed by the bias and variability of the primary clinical...
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Source Summarized from Temple 1982 . Source Summarized from Temple 1982 . baseline between captopril and placebo, reaches a plateau and remain constant after dosing period 2 during which 50 mg t.i.d. was administered. Consequently, Temple 1982 suggests that 50 mg t.i.d. seems to treat most hypertensive patients well. The design illustrated in Table 5.5.2 is an example of the optional titration design mentioned above. Inclusion of a parallel concurrent placebo control group can correct for...
Titration Designs
For phase I safety and tolerance studies, Rodda et al. 1988 classify traditional designs as follows 2. Rising single-dose crossover design. 3. Alternative-panel rising single-dose design. 4. Alternative-panel rising single-dose crossover design. 5. Parallel-panel rising multiple-dose design. 6. Alternative-panel rising multiple-dose design. As indicated in Chapter 1, phase I studies are usually conducted in young, healthy male volunteers. The purpose of phase I studies is to obtain initial...
Regulatory Process And Requirements
Chow and Liu 1995a indicated that the development of a pharmaceutical entity is a lengthy process involving drug discovery, laboratory development, animal studies, clinical trials, and regulatory registration. The drug development can be classified into nonclinical, pre-clinical, and clinical development phases. As indicated by the USA Today Feb. 3, 1993 , approximately 75 of drug development is devoted to clinical development and regulatory registration. In this section we will focus on...
Target Population And Patient Selection
As was indicated earlier, one of the primary objectives of a clinical trial is to provide an accurate and reliable clinical evaluation of a study drug for a target patient population with certain diseases. In practice, statistical and clinical inference are usually drawn based on a representative sample a group of patients to be enrolled in the trial selected from the target patient population of the clinical trial. A representative sample provides the clinician with the ability to generalize...
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In Chapter 2 we introduced some sources of bias and variation that can occur during the conduct of clinical trials. The control of bias and variability is extremely important to ensure the integrity of clinical trials. In comparative clinical trials, randomization is usually used to control conscious or unconscious bias in the allocation of patients to treatment groups. The purpose of randomization is not only to generate comparable groups of patients who have similar characteristics but also...
History Of Clinical Trials
We humans since our early days on earth have been seeking or trying to identify some interventions, whether they be a procedure or a drug, to remedy ailments that inflict ourselves and our loved ones. In this century the explosion of modern and advanced science and technology has led to many successful discoveries of promising treatments such as new medicines. Over the years there has been a tremendous need for clinical investigations of these newly discovered and promising medicines. In...
What Are Clinical Trials
Clinical trials are clinical investigations. They have evolved with different meanings by different individuals and organizations at different times. For example, Meinert 1986 indicates that a clinical trial is a research activity that involves administration of a test treatment to some experimental unit in order to evaluate the treatment. Meinert 1986 also defines a clinical trial as a planned experiment designed to assess the efficacy of a treatment in humans by comparing the outcomes in a...