WHAT IS A CLINICAL TRIAL?
Clinical Trial or Clinical Study - Definition
Any investigation in human subjects intended to discover or verify the clinical, pharmacological and/or other pharmacodynamic effects of an investigational product(s), and/or to identify any adverse reactions to an investigational product(s), and/or to study absorption, distribution, metabolism, and excretion of an investigational product(s), with the object of ascertaining its safety and/or efficacy. The terms "clinical trial" and "clinical study" are synonymous.
TESTING OF EXPERIMENTAL DRUGS IN HUMANS
Before a medication can be sold over the counter or with a prescription, it must undergo rigorous testing. The process by which new medications are tested so they may ultimately be marketed to treat or cure various diseases or conditions is as follows:
1. Development of a Compound
Chemists in a laboratory develop compounds with a certain chemical structure that the scientists believe may function in humans to alleviate certain symptoms in a disease, or perhaps even cure it.
2. Pre-clinical Testing
To prove that the compound works as is hypothesized and does not produce any negative side effects, it is first thoroughly tested in animals (e.g.., mice, rats, dogs, monkeys). This stage of testing is commonly referred to as the "pre-clinical" stage. The purpose of these animal studies is to prove that the drug is not carcinogenic (cancer causing), mutagenic (causing changes in the genetic material), or teratogenic (causing fetal malformations), and to understand how the drug is absorbed and excreted. Once a pharmaceutical company proves that the compound appears to be safe, and possibly effective in animals, the company will provide this information to the Food and Drug Administration (FDA) requesting approval to begin testing the compound (experimental drug) in humans via an Investigational New Drug (IND) application.
3. Clinical Trials/Studies in Humans
The clinical testing (investigation) of experimental drugs (previously unproven in humans, therefore "experimental") in humans is normally done in three phases (Phase I, II and III) with more and more people included in each subsequent phase. Although in general the phases are conducted sequentially, they may overlap. The three phases for testing experimental drugs are as follows:
- Phase I Clinical Studies
Phase I studies are primarily concerned with the drug's safety, and are the first time the drug is tested in humans. These studies are typically done in a small number of healthy volunteers (20-100), usually in a hospital setting where the volunteers can be closely watched and treated should there be any side effects. These volunteers are usually paid for their participation and for the most part tend to be men (approximately 30 years of age on average). The purpose of these studies is to determine how the experimental drug works in humans. That is, how is the drug absorbed, metabolized, and excreted. Additionally, they seek to determine what types of side effects occur as the dosage levels (that is, the amount of drug) are increased, as well as to obtain early evidence on drug effectiveness.
The PSG has not been involved in Phase I testing. However, it is during Phase I testing that the PSG is collaborating with the pharmaceutical company to plan Phase II and III clinical trials in Parkinson's disease.
- Phase II Clinical Studies
Once an experimental drug has been proven to be safe and well tolerated in healthy volunteers, it must be tested in the patients that have the disease or condition that the experimental drug is expected to improve/cure. In addition to ensuring that the experimental drug is safe and effective in the patient population of interest, Phase II studies are also designed to evaluate the effectiveness of the drug. The second phase of testing may last from several months to a few years and up to several hundred patients. Most Phase II studies are well controlled, randomized trials. That is, one group of patients (subjects) will receive the experimental drug, while a second "control" group will receive a standard treatment or placebo. Placement of the subject into the drug treatment or placebo group is by random chance (as if by the flip of a coin). Often these studies are "double-blinded", that is, the patient nor the researchers (investigator, coordinator, etc.) know who is getting the experimental drug. Additionally, Phase II studies are often designed to determine the correct dosage, that is the dosage with the least number of side effects that is most effective. These are often referred to as dose-ranging studies. In general, the purpose of Phase II studies is to provide the pharmaceutical company and the FDA comparative information about the relative safety of the experimental drug, the proper dosage, and the drug's effectiveness. Only about one-third of experimental drugs successfully complete both Phase I and Phase II studies.
The PSG has been heavily involved in the Phase II testing of numerous experimental drugs for PD. Many of these experimental drugs moved into Phase III testing and were ultimately approved by the FDA for use in PD.
- Phase III Clinical Studies
In a Phase III study, an experimental drug is tested in several hundred to several thousand patients with the disease/condition of interest. Most Phase III studies continue to be randomized and blinded. The large-scale testing provides the pharmaceutical company as well as the FDA with a more thorough understanding of the drug's effectiveness, benefits/risks, and range/severity of possible adverse side effects.
Phase III studies typically last several years. Seventy to 90 percent of drugs that enter Phase III studies successfully complete this phase of testing.
4. Marketing of New Drugs
After successful completion of Phase I-III testing, a company will submit the results of all of the studies to the FDA to obtain a New Drug Application (NDA). Once the FDA grants a company with a NDA, the company can market the drug (medication) to the public. Additional testing (post-marketing or late phase III/phase IV) to look at the long-term safety continues.
5. What about Natural Remedies
Patients are often interested in natural treatments of Parkinson's disease. It is important to understand that "natural" products are not subjected to the kind of rigorous testing outlined above. Therefore data are not always available for the safety or effectiveness of these treatments.
For more information about clinical trials, please go to ClinicalTrials.gov.
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