TYPES OF TRIALS

Before a new drug, surgical procedure, or therapy becomes available to the public, it must go through a rigorous testing process and be evaluated by the US Food and Drug Administration (FDA). This testing process consists of a series of clinical trials that are designed to test the safety and usefulness of the new drug compared to the current standard treatment. The clinical trials that make headlines are usually what are called phase III trials. These are large-scale tests with hundreds or thousands of patients. They are the culmination of earlier phase I and phase II trials that include many fewer people and still earlier preclinical experiments with animals. They are also the final tests in humans before the FDA is asked to authorize sale of new medicines.

Why Are Large-Scale Trials Needed? What Goes on Prior to a Large-Scale Phase III Trial? What Are the Different Types of Phase III Trials? What Happens After the Trials Are Over? What Questions Can't Be Answered by Phase III Trials?

Why Are Large-Scale Trials Needed?

Many volunteers are required because people are highly variable in how they respond to drugs Clinical trials are designed to test whether a drug is safe for humans, and whether the drug is effective in treating human diseases or conditions. Although the drug has generally gone through extensive animal testing before the trial begins, animal trials cannot always predict how new medicines will affect humans. Even the most painstaking tests with animals give only approximate indications of how people will respond to drugs. At some point, after thorough study in animals (and when the FDA is convinced human experimentation will probably be safe), tests with humans become necessary. Not only is it necessary to test new drugs in humans, but they need to be tested in a large number of humans in order for the results of the trial to be clear. The reason so many volunteers are required is that people are highly variable in how they respond to drugs. It is not unusual, for example, for a drug be somewhat effective in only 30 percent of those who take it. For medical researchers to prove such a slight benefit requires testing the drug in as many as several thousand patients. This extensive testing is part of what drives up the cost of new drugs – the average development time is over 10 years and costs from 500 to 700 million dollars.

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What Goes on Prior to a Large-Scale Phase III Trial?

Many volunteers are required because people are highly variable in how they respond to drugs An enormous amount of testing has gone on by the time a drug is ready for phase III. In general, a new drug or treatment goes through preclinical testing in animals, then small phase I and phase II trials in humans before being ready for large-scale testing. Preclinical testing When a drug is discovered that seems to have medical potential, a drug company will test it exhaustively in animals, looking for signs it may be poisonous, cause cancer, or cause birth defects. Animal studies will also be used to estimate the initial drug doses to be tested in humans. When animal experiments are finished, the company asks the FDA for permission to begin clinical trials. The FDA only grants approval once they are satisfied that the animal experiments are sound and that clinical trials are likely to be safe. Phase I Phase I trials are designed to find out if a drug is safe for humans The first test of the drug in humans is known as phase I. It is designed to find out if the drug is safe rather than whether the drug is effective. Phase I is also used to learn what drug doses to use in later trials, how the drug is broken down in the body and excreted, and study short-term side effects. A phase I trial rarely has more than 100 participants. Often healthy people are enrolled in phase I trials rather than patients on the assumption that if the drug has unexpected side effects, healthy people have the best chance of escaping permanent harm. But on other occasions, as with a drug treating a serious disease like cancer, phase I subjects may be patients who have failed standard treatments. Phase II Phase II trials are often the first time a drug is tested in actual patients If a drug passes the safety tests of phase I, it advances to a phase II trial with up to 200 participants. The goal of a phase II trial is to learn more about safety and side effects, sharpen estimates of proper doses, and get an early appraisal of whether the drug is going to work. This trial is often the first time a drug is tested in actual patients.

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What Are the Different Types of Phase III Trials?

The central question of a phase III trial is whether the drug works The phase III trial consists of hundreds or thousands of people. Commonly, phase III will be conducted at several medical centers to see if people treated in different locales have similar experiences. The central question of a phase III trial is whether the drug works. Phase III will also give doctors an extensive look at the drug's side effects. There are many different ways of conducting a phase III trial. Blinded, randomized trials Randomization is a way to help ensure that different groups in the trial have similar characteristics. This makes it easier to compare outcomes between groups Many Phase III trials are randomized, double-blind trials. Randomized means people are assigned at random either to receive the new drug, the standard treatment for that disease, or a nonfunctional substitute (such as a sugar pill). This last group is often called the control group, or the placebo group. Because phase III must answer definitively whether the drug works, it's important to compare people who receive it with others who do not. A good example of how people are randomly assigned to study groups is the phase III trial for Herceptin, which treats a form of breast cancer. In this trial women either received the standard breast cancer treatment with Herceptin or the standard treatment without Herceptin. In this case, there was no control group who received just a sugar pill because to do so would be to not treat women with a potentially fatal illness. In this trial, the women who received Herceptin with the standard treatment became the test group; the others, the controls. Women were assigned at random to the two groups. This means that the average age of the two groups was roughly similar as was the severity of their cancer so the results can be compared. If the two groups had differed considerably in age or health, researchers would not be able to tell if the drug itself was effective, or if the women in that group were just younger or healthier. Double-blind means that neither the doctor nor the trial participant knows whether the participant is receiving the experimental treatment Herceptin's trial was also considered double-blind, which means that neither the women nor their doctors knew who was receiving Herceptin. Of course, it is natural for doctors to want to know what treatments their patients are getting, and in single-blind trials they do. There, only the trial participants are unaware of which group they are in. But double-blind trials are considered better because they prevent doctors from acting on preconceived notions they may have about whether or not the drug works. For example, a doctor in the Herceptin trial might have been tempted to offer extra treatment to participants that weren't getting Herceptin. But the physician's attempt to compensate for the fact that the participant wasn't receiving the study drug would have collided with the requirement to keep groups comparable in everything except who received the new drug. Unintentionally, the doctor might have interfered with the trial, casting doubt on its conclusions. This is why it is considered good practice for phase III trials to be double-blind. Open trials Not every trial is blind. In unblinded trials, often described as open trials, both doctors and participants know what treatments are being given. Trials of surgical procedures and comparisons of medical devices are often by nature open. One of the problems with an open drug trial is that many participants may not want to take placebos, because they presume the drug will be better. Open trials, like single-blind trials, are considered to be more prone to error than double-blind procedures. Factorial trials When patients are being treated with a combination of drugs, as is current practice for HIV infection, a new drug may be evaluated by testing it in combination with other drugs rather than by itself. A factorial design trial may be used for this purpose. A simple factorial design would have one group testing therapy A, another testing therapy B, a third group testing A and B combined, and a control group testing neither A nor B. Factorial designs are considered an efficient way to test medicines in combination, but their results are not always easy to interpret. Crossover trials In a crossover trial, each participant gets both treatments being tested. Some participants are assigned at random to receive drug A, and later, drug B. Others receive B, then A. To produce valid results, the effect of the first drug must end before the second drug is taken, and vice-versa. This requirement can be hard to satisfy, and is one reason crossover trials are not often used. Orphan Drug Trials Orphan drug trials test drugs designed to treat diseases affecting fewer than 200,000 Americans. Some are rare genetic diseases that occur when missing or defective enzymes prevent essential biochemical reactions from happening. Because affected individuals are so few, an orphan drug may be tested only on a small number of participants, who generally are so sick that if the drug works, their improved health is readily apparent.

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What Happens When the Trials Are Over?

After a successful phase III trial, FDA approval moves the drug into everyday medical practice When the trials end, the drug company submits its data to the FDA and asks for permission to market the drug. The FDA approves the drug if it agrees that the drug is safe and effective. If it isn't convinced, the agency will reject the application or may request additional data before making a final decision. Approval moves the drug into everyday medical practice. The FDA then begins surveillance of side effects experienced by patients within the general population. Finally, there is the question of what happens to you if you benefit from a drug in a clinical trial and need to continue using it between the time the trial ends and the FDA grants approval. Especially for serious diseases, the FDA sometimes allows companies to distribute drugs prior to approval on grounds of compassion.

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What Questions Can't Be Answered by Phase III Trials?

Even after phase III trials, certain side effects may remain unknown. For example the trials may not have included enough people to detect rare side effects, or the drug may show harmful interactions with a common medication. After the drug enters the market and many thousands of people start taking it, these rare side effects and drug interactions can surface. If the side effects are severe the FDA has to take action. It may require stronger side effect warnings, narrow conditions for the drug’s use, or even force it to be withdrawn from the market.

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interview questions

Most Common Interview Questions:
What do you think is the role of Clinical Research Associate (CRA) in a Clinical Research Organization?
What are the steps involved in planning and conducting a study?
Which regulating bodies oversee workings of a CRO?
What is a healthy volunteer?


What are different types of trials that a CRO can conduct?
How will you deal with inconsistency in the analytical data?
How will you select File parameters for Mass Spectrometer?
On what basis are sample time points for the study selected?
What is the difference between Bio-availability study and Bio-equivalence study?
What is the difference between ANDA and NDA?
What is the composition of Ethical committee?
What constitutes Adverse event how will you deal with it?

Interview questions related to plasma and extraction and method development
What is matrix effect?
How matrix effect can be determined?
How matrix effect can be minimized?
What is recovery?
Criteria for recovery?

Interview questions related to bio method validation
What are the fundamental validation parameters, explain each?
What is selectivity?
What is the calibration curve?
What should consist in calibration curve?
What do you mean by stability?
Explain different types of stability?
Explain Precision and Accuracy?

What are clinical trials?

A clinical trial is a research study in human volunteers to answer specific health questions. Carefully conducted clinical trials are the safest and fastest way to find treatments that work in people, and new ways to improve health.

There are different kinds of clinical trials, including those to study:

• prevention options
• new treatments or new ways to use existing treatments
• new screening and diagnostic techniques
• options for improving the quality of life for people who have serious medical conditions

Clinical trials are conducted according to a plan called a protocol. The protocol describes what types of patients may enter the study, schedules of tests and procedures, drugs, dosages, and length of study, as well as the outcomes that will be measured. Each person participating in the study must agree to the rules set out by the protocol.

2. Why are clinical trials done?

Many clinical trials are done to see if a new drug or device is safe and effective for people to use. Clinical trials are also done for other reasons. Some compare existing treatments to determine which is better. The current, approved treatments are called the "standard treatments." Sometimes clinical trials are used to study different ways to use the standard treatments so they will be more effective, easier to use, and/or decrease side effects. Sometimes, studies are done to learn how to best use the treatment in a different population, such as children, in whom the treatment was not previously tested.

For most trials, researchers, doctors, and other health professionals administer the clinical trials according to strict rules set by the Food and Drug Administration (FDA). FDA sets the rules to make sure that people who agree to be in studies are treated as safely as possible.

3. Where can people find out about clinical trials?

People can find information about clinical trials now being conducted now by searching clinicaltrials.gov². ClinicalTrials.gov is an interactive online database, managed by the National Library of Medicine. It provides information about both federally and privately supported clinical research in human volunteers. ClinicalTrials.gov is updated regularly and offers information on each trial's purpose, who is eligible to participate, locations, and phone numbers to call for more information.

Since ClinicalTrials.gov is only available online, individuals without Internet access can use the database at the public library or other publicly available internet portal.

4. What types of clinical trials are available?

There are many different kinds of clinical trials, including:

• trials that test new treatments, new combinations of drugs, or new approaches to surgery or radiation therapy.
• Prevention trials, that look for better ways to prevent disease in people who have never had the disease or to prevent a disease from returning. These approaches may include medicines, vitamins, vaccines, minerals, or lifestyle changes.
• Diagnostic trials, that are conducted to find better tests or procedures for diagnosing a particular disease or condition.
• Screening trials to test the best way to detect certain diseases or health conditions.
• Quality of Life trials (or Supportive Care trials), that explore and measure ways to improve comfort and the quality of life for individuals with a chronic illness.

Usually, clincal trials compare a new product or therapy to something else to see if it works as well or better to treat or prevent a disease or condition. In a blinded study, a participant may be randomly assigned to receive the test product, or an existing, approved therapy. In some studies, participants may be assigned to receive a placebo (a product with no therapeutic action that looks like the test product). Comparison with a placebo can be the fastest and surest way to demonstrate therapeutic effectiveness of new products. However, placebos are not used where a patient would be put at risk, particularly in the study of treatments for serious illnesses, by not having effective therapy. Most studies of this kind compare new products to an approved therapy. Potential participants are told before they enter a trial whether placebos are going to be used in the study.

5. Who should consider clinical trials and why?

It is important to test drugs and medical products in the people they are meant to help. It is also important to conduct research in a variety of people because different people may respond differently to treatments. FDA seeks to ensure that people of different ages, races, ethnic groups, and genders are included in clinical trials.

Some people participate in clinical trials because they have exhausted standard (approved) treatment options - which either did not work for them, or they were unable to tolerate certain side effects. Clinical trials may provide another option when standard therapy has failed.

Other people participate in trials because the want to contribute to the advancement of medical knowledge.

For each clinical trial, researchers develop eligibility criteria, such as the age, sex, type and stage of disease, previous treatment history, and other medical conditions. These criteria help to reduce the amount of variation in the study, without threatening the scientific integrity of the trial, by removing medical variations that might complicate analyzing the results.

Not everyone who applies for a clinical trial will be accepted. Volunteers may be excluded based on the eligibility criteria and/or the number of participants needed by the researchers to collect enough information to determine the safety and effectiveness of a therapeutic agent.

6. Where are clinical trials conducted?

Clinical trials can be sponsored by an organization such as a pharmaceutical company, a federal agency - for example, the National Institutes of Health or Veterans Administration -or an individual, such as a physician or health care provider. The sponsor determines the location(s) of the trials which are usually conducted at universities, medical centers, clinics, doctor's offices, and/or at hospitals, federally- and industry-funded research sites.

7. Are clinical trials safe?

The FDA works to protect participants in clinical trials and to ensure that people have reliable information as they decide whether to join a clinical trial. The federal government has regulations and guidelines for clinical research³ to protect participants from unreasonable risks.

Although efforts are made to control the risks to clinical trial participants, some risks may be unavoidable because of the uncertainty inherent in medical research studies involving new medical treatments.

The government requires researchers to give prospective participants complete and accurate information about what will happen during the trial. Participants must sign an "informed consent" document before joining the study indicating they understand that the trial is research, and that they can leave the clinical trial at any time. This informed consent is part of a process that ensures a prospective participant in a clinical trial understands what known risks might be associated with the study, and whether there are potential, but as yet unknown risks that may be associated with the product being studied. This information permits someone deciding whether or not to enter a clinical trial to make an informed decision about the level of risk they are willing to accept before they enter the trial.

8. What should people think about before joining a clinical trial?

People should learn as much as possible about the clinical trials that interest them. They should also feel comfortable discussing their questions and concerns with members of the health care team. Prospective participants should understand what happens during the trial, the type of health care they will receive, and any costs to them - which may or may not include the cost of the product, costs associated with administering the product, etc.

Anyone considering a clinical trial should also know that there are benefits and risks associated with participating.

Potential Benefits

Participating in well-designed and well-executed clinical trials is one approach for eligible patients/volunteers to:

• get actively involved in their health care.
• gain access to potentially new research treatments
• have access to expert medical care for the condition being studied, since investigators are often specialists in the disease area being studied.
• help others by contributing to medical research.

Possible Risks

There are generally known and unknown risks associated with clinical trials, such as:

• there may be unpleasant, serious, or even life-threatening side effects resulting from the treatment.
• the treatment may not be effective for the participant.
• the protocol may require more of the participant's time and attention than a standard treatment. (Participants may need to visit the study site on a regular basis, be subjected to additional tests, get more treatments than are normally necessary, stay in the hospital and/or follow complex dosage requirements.)

Other considerations:

Payment/compensation:

• Subjects are sometimes paid for their participation in research, especially in the early phases of investigational drug, biologic or device development. Payment to research subjects for participation in studies is considered a a recruitment incentive. Financial incentives are most often used when health benefits to subjects are remote or nonexistent. Volunteers may be offered compensation in certain trials for their time, and for discomfort that may be experienced during the trial. The amount of compensation is determined by the amount of time you will be required to dedicate to the trial, and to the level of discomfort that might be associated with medical or surgical procedures related directly to the study. Payment information, including the amount and schedule of payment(s), as well as any possible costs to volunteers who participate in a study, are discussed with potential participants during the informed consent process, and documented in the informed consent form.

Potential Conflict of Interest:

• Some health care workers are paid fees for recommending, referring, or enrolling patients in clinical trials. This information is generally not discussed during informed consent, but potential volunteers may ask if the referring health care provider will receive monetary compensation, or if investigators have other potential conflicts of interest.

Continued Treatment:

• Will the treatment be stopped at the end of the trial, even if the participant feels it is beneficial? Some sponsors continue to provide product. Others do not.

9. What's the role of the FDA in approving new drugs & medical treatments?

The Food and Drug Administration's job is to make sure medical treatments are safe and effective for people to use. However, FDA does not develop new therapies, or conduct the clinical trials to demonstrate safety and effectiveness. FDA staff members meet with researchers, and perform inspections of clinical trial study sites to protect the rights of participants and to verify the quality and integrity of the data.

trails phases

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. Before moving to the next phase of development the data are carefully analyzed to ensure the experimental drug is at least safe and well tolerated. After successful completion ofPhase I-III testing, a company will submit the results of all of the studies to the FDA or TPD to obtain a New Drug Approval (NDA). Once the FDA or TPD 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 ongoing-term safety continues.

Phase I 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 they 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. (Women and children would be involved only in latest phases of clinical trial and only if substance in question is designed to be used in this groups of population.) The purpose of Phase I studies is to determine how the experimental drug is absorbed, metabolized, and excreted in humans. Additionally, they seek to determine what types ofside effects occur as the dosage of the drug is increased. Any beneficial effects of the drug are also noted. Phase I studies test a particular treatment in humans after it has been studied in the laboratory. The purpose of Phase I studies is to determine the maximum tolerated dose or amount of the treatment and answer questions about the best way to give the new treatment. Drugs that can cause seriousside effects are not tested on healthy humans, for example drugs for treating cancer. Phase I of these studies is carefully controlled by Cancer Therapy Evaluation Programs.

The following pre-clinical studies must be completed before phase 1 studies can begin in the United States.


Single dose toxicity in two mammalian species.Safety pharmacology studies to include assessment of effects on vital functions.Pharmacokinetic studies (ADME)Repeated dose toxicity studies in two species (one non-rodent) for two to four weeks, providing phase 1 studies will not exceed two weeks.Local tolerance studies using route of administration relative to propose clinical administration.In vitro tests for evaluation of mutations and chromosomal damage (genotoxicity)Carcinogenicitystudies (only if there is cause for concern)

Source: Safety Studies for the Conduct of Human Clinical Trials for Pharmaceuticals, U.S. Department of Health and Human Services and the FDA (CDER and CBER), July 1997, ICH.


Phase II Studies

Once Phase I studies have been completed and a dosage level is known, Phase II studies can start. 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 IIstudies 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 may involve up to several hundred patients. Most Phase II studies are well controlled, randomized trials. That is, one group of patients (subjects) receives the experimental drug, while a second "control" group receives 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 thesestudies 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 in USA and TPP/TPD in Canada with comparative information about the relative safety of the experimental drug, the proper dosage needed to treat the condition, and the drug's effectiveness. Only about one-third of experimental drugs successfully complete bothPhase I and Phase II testing.

Pre-clinical requirements before initiating phase II studies in the U.S.:
Repeated dose toxicity studies in two species (one non-rodent) for a period of time equivalent to the length of the phase II studies. Six-month rodent and chronic non-rodent studies will support clinical trials of six months’ duration in the U.S. Studies of longer treatment duration are supported by nine- to twelve-month long pre-clinical studies.

Source: Safety Studies for the Conduct of Human Clinical Trials for Pharmaceuticals, U.S. Department of Health and Human Services and the FDA (CDER and CBER), July 1997, ICH.

Phase III Clinical Studies

If the treatment is found to be effective, Phase III studies compare it to the standard treatment. This is done by having two or more "arms" of treatment in which patients are randomly selected to participate. The arm in which the patient participates is decided by chance (by a computer), not choice. This randomization assists in making the groups as equal as possible so that sound conclusions can be drawn from study results. Patients are randomized by a number of factors that may affect the outcome of the study (age, performance status, stage of disease, etc.). In all treatment arms, patients should receive the best care available. The Data Monitoring Committee oversees all Phase III studies conducted by Sponsor. 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-scaletesting 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 adverseside 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.

Pre-clinical requirements for initiation of phase III studies in the U.S.:

Repeated dose toxicity studies in two species (one non-rodent) for a period of time equivalent to the length of the phase III studies. Six-month rodent and chronic non-rodent studies would support clinical trials exceeding six months.Carcinogenicity studies if the duration of treatment of the drug is expected to be six months or longer or if intermittent exposure is equal to six months of continuous exposure, or if there is a cause for concern. Carcinogenicitystudies are not required if the patients receiving the drug have life expectancy of less than two years.Fertility studies in males.Repeated dose toxicology studies that include an evaluation of female reproductive organs must be done if women of non-childbearing potential are used.Assessment of female fertility and embryo-fetal development if women of childbearing potential will be included.All reproduction toxicitystudies and the standard and the standard genotoxicity tests should be completed if pregnant women will be included.

Source: Safety Studies for the Conduct of Human Clinical Trials for Pharmaceuticals, U.S. Department of Health and Human Services and the FDA (CDER and CBER), July 1997, ICH.

Phase IV Marketing of New Drugs and Post - Marketing Surveillance
After successful completion of Phase I-III testing, a company submits 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. Kriger Research Center has a couple of full scale independent projects andstudies on several groups of new drugs in post-marketing stage. FDA (in USA) or TPD (in Canada) may require that sponsor would do a long term safety study - epidemiological post-marketing surveillance, as a condition of approval, These may be required because there have been seen problems with similar compounds in the past, or because the compound is novel and additional safety information will be beneficial.

clinical trials

A clinical trial is designed to answer specific questions about new drugs, medical devices, or new ways of using known treatments.

Clinical trials are used to determine whether the new drug or treatment is safe, and whether it works.

Clinical trials consist of four phases:

Phase I tests a new treatment on a small group, and concentrates on safety;

Phase II deals with safety and efficacy, and expands the study to a larger group of people (several hundred);

Phase III expands the study to an even larger group of people (thousands), and is designed to determine conclusively whether or not the treatment is effective;

Phase IV takes place after the drug has been licensed, to monitor the drug for long-term effects.

The randomized, double-blind, placebo-controlled (or active-comparator-controlled) trial offers the strongest evidence that a treatment is effective. The number of participants also considerably effects how reliably the trial can determine the effects of a treatment.

Clinical trials must be consistent with good clinical practice (GCP), a rigorous set of guidelines designed to protect the participants’ safety and the integrity of the trial data. The FDA requires pharmaceutical companies and contract research organizations to conduct rigorous clinical trials verifying the safety and efficacy of the new drugs before granting approval for marketing.

The trial objectives and design are usually documented in clinical trial protocols. Once the objectives are determined, case report forms must be carefully designed to gather complete, unambiguous data from the trial.

During the trial, the data management team must continually monitor and verify the data to ensure that they are accurate and consistent. Any missing or inconsistent data must be investigated and corrected.

stem cell research

Stem cell research is intended to lead to the development of an infinitely renewable source of cells for cell-replacement therapies to treat disease. Embryonic stem cells, derived from 5–7 day old embryos, differ from other cells in the body in that they are both capable of self-renewal (i.e., able to divide and renew themselves), and are pluripotent (i.e., can differentiate into many kinds of specialized cell types, such as muscle or neuronal tissue). Research into embryonic stem cells seeks to identify precise approaches that would allow scientists to direct stem cell differentiation into specific tissue types, creating a source of tissue for transplantation to replace damaged tissues. Conditions such as Parkinson’s disease (see box below), spinal cord injury, muscular dystrophy, heart failure, and diabetes could conceivably be treated using these replacement cells.Progenitor cells, also called adult stem cells or somatic stem cells, are isolated from specific bodily tissues. Like embryonic stem cells, they are capable of self-renewal, but can differentiate into only a restricted range of tissues. For example, hematopoietic stem cells can differentiate into red blood cells, white blood cells, and platelets, while pancreatic progenitor cells can differentiate into insulin-secreting islet cells. The primary role of progenitor cells is to replenish the tissue from which they are cultured. Hematopoietic stem cells have been used in bone marrow transplants for the treatment of leukemia. The umbilical cords of newborn infants provide a source of cord progenitor cells that have hematopoietic origins. Stem Cells for the Future Treatment of Parkinson’s