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Phases of Clinical Research

Each phase of clinical research has its own unique goals and challenges. While clinical research is generally divided into four phases, two additional stages are sometimes part of the process:

Preclinical Study Phase

Preclinical studies are conducted before clinical research begins and typically involve in vitro and in vivo studies to collect data pertaining to the efficacy, toxicity, and pharmacokinetics of a drug, vaccine, or diagnostic assay.  Only when the results of such studies are favorable will the development of a drug move forward.

Phase 0

Phase 0 is not always considered part of the clinical research process, so Phase1 is more commonly regarded as the first clinical trial phase. Essentially, Phase 0 is a new designation for exploratory trials undertaken in accordance with the FDA’s Guidance on Exploratory Investigational New Drug (IND) Studies. 

Phase 0 involves human microdosing studies meant to expedite the development of promising new drugs by establishing that they behave as expected based on preclinical studies. 

Subtherapeutic doses are administered to a small group of human subjects to collect preliminary data on a drug’s pharmacokinetics. 

This phase is not concerned about safety or efficacy and is often carried out to rank different drug candidates to find the one with the best pharmacokinetic parameters. 


Phase 1

As noted above, Phase 1 is regarded as the start of formal clinical research and is described as a first in human study. During this phase, researchers test the safety, side effects, dosage, and formulation of a drug with a small group of voluntary human subjects. Usually, 20 to 100 people are recruited, and trials are conducted in a clinic where full-time staff can observe trial volunteers. 

In most cases, volunteers are healthy, but in certain circumstances, patients who have terminal cancer, HIV, or other conditions are recruited instead, as treatments for such diseases may make healthy subjects ill. 

Phase 2

After a range of doses is settled upon during the first phase of clinical research, the second phase studies the drug on a larger group of subjects to determine its safety and efficacy. Phase 2 is often divided into two sub-phases; the first is a pilot study focused on effectiveness and biological activity, while the second determines the optimal dose.

Phase 3

Next, we move to Phase 3 of clinical research, which weighs the overall effectiveness of the drug and its value in clinical practice compared to the current dominant treatment for a disease or condition. 

There are many test subjects, making this phase one of the most expensive, difficult, and time-consuming.

Phase 4

Phase 4 is also known as postmarketing surveillance or drug monitoring, as it involves ongoing surveillance after a final dosage form has received regulatory approval.


Resource Person: BARBARA PIROLA

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