Developing a drug or a therapeutic regimen is a complex, long, and expensive process. Before a pharmaceutical or biotechnology company can begin marketing its products, it must undergo a rigorous review process to gain approval from the various regulatory authorities in the market. This process can take several years and requires substantial investment.

This article will overview the process of drug discovery, preclinical, and clinical development leading up to regulatory approval. It will discuss the steps and stages involved, the challenges and timelines associated with developing drugs for serious bacterial infections such as C. difficile, and the importance of filing regulatory applications.

Drug Discovery

Drug discovery is the process of identifying compounds that are effective therapeutic agents. It combines laboratory research, computational analysis, and medicinal chemistry. The goal is to develop a molecule that is effective for treating a given pathogen that can safely be administered to patients. For a compound to be a candidate for development into a drug, the compound must offer potential for having a therapeutic effect on the disease that it would be developed to treat.

It is no easy feat to develop a new drug – only 5,000 of the 10,000 potential candidates make it to the preclinical testing stage and an even smaller fraction, just 1 in 5,000, ultimately receive market approval. This speaks to the complexity and dedication required for development [1].

Drug discovery typically starts with the identification of a target molecule. This is followed by several rounds of chemical synthesis and testing to identify molecules interacting with the target and having the desired therapeutic activity. Such molecules are then evaluated and refined to create potent compounds with optimal pharmacological and pharmacokinetic properties.

Preclinical Development

Once a drug candidate is identified, preclinical development begins. This stage involves a series of in vitro and in vivo studies to demonstrate the safety and efficacy of the drug. In vitro refers to studies done outside of a living organism and in vivo refers to studies performed within a living organism [2]. The results of these studies are used to develop a drug formulation, determine appropriate dosing, and establish toxicity profiles.

The core objective of the preclinical stage is to evaluate whether the product is safe for human use and possesses enough pharmacological potency to be considered viable for advancement into a commercial setting [3].

At the end of preclinical development, a detailed report on the drug’s safety, efficacy, and pharmacology is submitted to regulatory authorities in the market. This is known as an Investigational New Drug (IND) application. The submission of the IND application is the first step toward regulatory approval [3].
The IND Application must include information in three distinct categories to be considered for authorization by the FDA. These consist of [3]:

  • Toxicology and Pharmacology – details the overall safety of the drug in question [5].
  • Manufacturing Information – pertains to the composition of the drug chemically, as well as the specific methods needed to produce it, and the controls and stability used in the manufacturing of the drug [5].
  • Investigator Information and Clinical Protocols – included will be a very detailed report of the protocols for the clinical study of the drug, as well as qualifications that investigator must meet to be a clinical investor for the study [5].

If the application is approved by the FDA, meaning that it is reasonable to believe that participants in a clinical study will not be exposed to unreasonable risks, then the drug can enter a Phase 1 clinical trial [5].

Clinical Development

Clinical development involves testing the drug in humans to assess safety and efficacy. It is divided into three phases, each consisting of different studies. The first phase entails the initial testing of the drug in a small number of healthy volunteers and/or patient populations. During this phase, investigators evaluate dosage, safety, efficacy, pharmacokinetics, and side effects [4].

The second phase builds on the data generated in phase one and involves more extensive testing in sometimes larger patient populations. This phase is designed to provide additional information on the drug’s effectiveness, safety, and tolerability [4].

The third phase, which is the final phase before filing a New Drug Application (NDA), is the definitive clinical trial of the drug. It involves testing the drug in large patient populations and comparative studies with existing treatments. At the end of this phase, a detailed report is compiled and submitted as part of the NDA for review by the regulatory authority.

Filing Regulatory Applications

The submission of regulatory applications is a crucial step toward commercializing a drug. Depending on the market, this could involve submitting an IND application, a New Drug Application (NDA), and/or a Marketing Authorization Application (MAA). These applications provide the FDA and other regulatory authorities with detailed information on the safety and efficacy of the drug.


The process of developing a drug or therapeutic regimen is long and complex. It involves several stages: drug discovery, preclinical development, clinical development, and regulatory approval. Although the process is laborious and expensive, it is necessary to ensure that new drugs developed are safe and effective. With the help of advanced technology, scientists and clinicians strive to make this process faster and more efficient. Ultimately, their efforts are aimed at saving lives and improving patient outcomes.


  1. “The Drug Discovery Process: What Is It and Its Major Steps.” BioBide,
  2. Lakna. “Difference between in Vitro and in Vivo: Definition, Facts, Examples, Differences.” Pediaa.Com, 4 June 2019,
  3. Center for Drug Evaluation and Research. “Investigational New Drug (IND) Application.” U.S. Food and Drug Administration, FDA,
  4. Center for Drug Evaluation and Research. “The FDA’s Drug Review Process: Ensuring Drugs Are Safe and Effective.” U.S. Food and Drug Administration, FDA,
  5. “The Regulatory Process.” CISN,