Early Drug Development: The phase of drug development in which synthetic small molecule compounds or biological molecules are identified and selected for further development as leads. This process typically includes assay development, high throughput screening, identification of "hits" that have activity in a test tube, characterization of hits and selection of lead molecules for further optimization. The early drug development process often takes several years to produce drug leads.
Lead Optimization: The improvement of hit compounds that have been identified as "leads" in early drug development. Lead optimization focuses on improving properties of compounds including efficacy, potency, exposure, safety, and stability in order to make them more drug-like. The goal of lead optimization is to identify a compound (Development Candidate) suitable for preclinical development.
Preclinical Development: This stage consists of testing a Development Candidate in various in vitro and in vivo assays to examine its safety pharmacology and toxicology profile; these evaluations are collectively also known as IND-enabling studies. This stage also includes a scale-up manufacturing of the Development Candidate and preparation for clinical trials. The end result and goal of testing in the preclinical stage is submission of an IND application to the Food and Drug Administration (FDA).
IND – Investigational New Drug: A request to the FDA for authorization to administer an experimental drug or biological product to humans. This application precedes the start of clinical trials.
Phase I Trials: Initial studies to determine the safety and pharmacokinetics of drugs in humans, and the side effects associated with increasing doses; in some cases the studies can also be used to gain early evidence of effectiveness. Healthy participants and/or patients may be recruited for this first phase of clinical trials.
Phase II Trials: Clinical studies conducted to evaluate the effectiveness of a drug for a particular disease or signs or symptoms in patients with the disease or condition under study, and to determine the common short-term side effects and risks associated with dosing.
Phase III Trials: Expanded trials which take place after review of preliminary safety and efficacy data from Phases I and II; the intent of Phase III trials is to gather additional information to evaluate the overall benefit-risk relationship of the drug. After Phase III is completed, a New Drug Application (NDA) or Biologic License Application (BLA) can be submitted to the FDA for approval of the drug for marketing.
Phase IV Trials: Post-marketing (i.e. post-approval) studies designed to provide additional information on the drug which may include the drug’s risks, benefits, and optimal use. These studies may be voluntary or required by regulatory agencies as part of their approval for marketing.