Definitive clinical efficacy studies

Many of the issues relating to the definition of nonchni-cal laboratory study were addressed in the discussion of GLP 58.1 (Scope). Field trials in animals includes all efficacy studies of new animal drugs. Such studies are outside the scope of the GLP regulations. This is consistent with the GLP exemption for human clinical trials. The exemption for basic exploratory studies carried out to determine whether a test article has any potential utility would extend to early screening studies of a test article, the results of which are used to determine whether a test article merits further development or not. 

Phase III studies represent the confirmatory phase of drug development, which takes several years and usually involves several thousand patients at multiple trial centers. Large patient numbers are required in these trials to provide convincing documentation of clinical efficacy and safety, a more complete adverse event profile and covariates and estimates of variability in dose response relationship due to individual differences in pharmacokinetics and pharmacodynamics. They are aimed at definitively determining a drug s effectiveness and side-effect profile. Most of these studies are double-blind and placebo-controlled, sometimes with the option of open-label long-term extensions. 

Clinical trials and clinical trial authorizations in the European Union are controlled under the Clinical Trial Directive, 2001/20/EC [9], and all member states are bound by its requirements. Under the provisions of the Directive, a clinical trial is an investigation in human subjects that is intended to discover or verify the clinical, pharmacological, and/or other pharmacodynamic effects of one or more medicinal products, identify any adverse reactions or study the absorption, distribution, metabolism, and excretion, with the object of ascertaining the safety and/or efficacy of those products. This definition includes pharmacokinetic studies. 

This section describes some of the biological research experiments that could, and in most cases should, be conducted to evaluate the potential of a lead compound to become a developmental candidate. Figure 3 shows where these developability experiments fit into the drug discovery and development process. These nondefinitive developability studies may also uncover problems that have to be resolved before the definitive preclinical development studies required to support an IND submission are started and before the clinical protocols to evaluate the safety and efficacy of the drug candidate in humans are designed. 

Phase II clinical trial studies are designed primarily to explore the relationship between the dose level and frequency of administration and the efficacy and safety observed in patients with a particular therapeutic indication or disorder. Normally, a primary endpoint is selected to evaluate the efficacy however, secondary endpoints are often included to establish criteria for monitoring patients in the more definitive phase III clinical trials. Phase II clinical trials are commonly... 

The overall objective of clinical trials is to establish a drug therapy that is safe and effective in humans, to the extent that the risk-benefit relationship is acceptable. The ICH process has developed an internationally accepted definition of a clinical trial as Any investigation in human subjects intended to discover or verify the clinical, pharmacological and/or other pharmacodynamic effects of one or more investigational medicinal product(s), and/or to identify any adverse reactions to one or more investigational medicinal product(s) and/or to study absorption, distribution, metabolism and excretion of one or more investigational medicinal product(s) with the object of ascertaining its (their) safety and/or efficacy. ... 

Tables 2A and B summarize the results of clinical studies that assessed the efficacy of rifaximin in the treatment of bacterial diarrhea. Many of the studies suffer from small numbers and not uniform definitions of diarrhea. In the studies of DuPont et al. [6, 13], acute diarrhea was defined as three or more unformed stools passed in a 24-hour period accompanied by at least one symptom of...

Phase IV. Studies or trials conducted after a medicine is marketed to provide additional details about the medicine s efficacy or safety profile. Different formulations, dosages, durations of treatment, medicine interactions, and other medicine comparisons may be evaluated. New age groups, races, and other types of patients can be studied. Detection and definition of previously unknown or inadequately quantified adverse reactions and related risk factors are an important aspect of many Phase IV studies. If a marketed medicine is to be evaluated for another (i.e., new) indication, then those clinical trials are considered Phase II clinical trials. The term postmarketing surveillance is frequently used to describe those clinical studies in Phase IV (i.e., the period following marketing) that are primarily observational or nonexperimental in nature, to distinguish them from well-controlled Phase IV clinical trials or marketing studies. 

Phase I studies evaluate the pharmacokinetics and safety of the drug in a small number (tens) of healthy volunteers. Phase I studies are sometimes conducted in a small patient population (Proof of Concept studies) with a specific objective such as the validation of the relevance of preclinical models in man. The purpose of these studies may be the rapid elimination of potential failures from the pipeline, definition of biological markers for efficacy or toxicity, or demonstration of early evidence of efficacy. These studies have a potential go/no-go decision criteria such as safety, tolerability, bioavailability/PK, pharmacodynamics, and efficacy. Dosage forms used in Phase I or Proof of Concept studies must be developed with the objectives of the clinical study in mind. 

These issues must be kept in mind when interpreting claims made on the basis of clinical trial results. The variability in scales and definition of terms used in antidepressant trials also confounds attempts to make comparisons across studies and to do meta-analyses. With these caveats in mind, the next several sections review the acute and maintenance efficacy of the available antidepressant options, as well as some currently investigational antidepressants. 

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