SciDev.Net
Science and Development Network
News, views and information about science, technology and the developing world
Definitions
In this section you will find a directory of terms used in the field of research ethics. Several have been reproduced from the Nuffield Council on Bioethics.
Developing countries are increasingly recognising the importance of science in developing their economies, and the challenges that entails.
P
Perinatal transmission
Transmission of an infection-causing agent (such as HIV) from mother to child in the period either shortly before or after birth. [Source: Nuffield Council on Bioethics]
Phase I trials
Phase I trials are the first time that human subjects are exposed to a potential novel medicine. The objectives behind the study will be to investigate the biochemical and physiological effects of the drug and its mechanisms and, in the case of vaccines, immune response, and to determine the maximum dose that can be tolerated by participants. In the case of most new medicines these studies will be undertaken in a small number of healthy volunteers. It is not expected that evidence of the medicine's efficacy will be provided by Phase I trials. (See also clinical research.) [Source: Nuffield Council on Bioethics]
Phase II trials
Using information regarding the safe dosage range obtained from the Phase I studies, the compound is administered to patients suffering from the target disease. Almost always these trials will be conducted in a number of clinical centres and will include significant numbers of individuals. The objective of the Phase II trials is to seek evidence of the efficacy of the medicine against the specific disease. More information about the safety of the medication will emerge from these studies as larger numbers of individuals are exposed to it. In Phase II trials the patient will often be randomly assigned to the novel treatment group or to a group receiving a placebo (a compound possessing no therapeutic effect) or, more usually, a conventional and established treatment. (See also clinical research.) [Source: Nuffield Council on Bioethics]
Phase III trials
Where a compound has shown evidence of efficacy without significant side effects it will enter Phase III trials in which many hundreds, or sometimes a few thousand patients will be enrolled. These trials generally seek not only to confirm the clinical efficacy of the novel compound, but also to establish its efficacy in comparison with existing treatments. These studies areoften multi-centre and sometimes undertaken on an international basis. Again, careful attention is paid to possible side effects as larger numbers of patients are exposed to the intervention. The end-points for Phase III studies include demonstration of a statistically significant improvement in the efficacy of the novel medicine over established therapies, if any such exist. (See also clinical research.) [Source: Nuffield Council on Bioethics]
Phase IV trials
Once a new medicine reaches the market it is subjected to post-marketing surveillance in order to identify side-effects and other adverse effects which only become evident as much larger numbers of individuals are treated with it. In addition, formal clinical trials continue in order to develop a greater understanding of the compound and its effects in a wider clinical environment, but also to extend its use for other indications or for different patient groups, such as children or the elderly. Special study designs may be used according to the objectives of the study to evaluate safety or efficacy, and may include the study of temporal trends, case-control studies, or the phased introduction of an intervention in different areas. Phase IV trials may also be designed to measure the impact of the intervention on the epidemiological pattern or transmission of an infectious disease. (See also clinical research.) [Source: Nuffield Council on Bioethics]
Placebo
A treatment known to be without effect, usually used as a control to be compared against a potentially effective substance or method which is being subjected to clinical trial. [Source: Nuffield Council on Bioethics]
