Glossary for the Antibiotic Pipeline

Glossary for the Antibiotic Pipeline

This glossary was updated in September 2019 to include additional terms.

Clinical trial1: A research study that uses human volunteers to help test the safety and/or efficacy of new treatments for diseases and conditions.

Drug class: Molecules that share a common principal chemical scaffold, or specific arrangement of atoms, belong to a common drug class. For example, quinolone antibiotics share a distinctive ring system at their core.

Drug development2: The process of rigorously testing a new drug candidate for safety and efficacy in order to bring it to market. The U.S. Food and Drug Administration (FDA) reviews the results of this testing, as well as manufacturing information, before it will consider approving a drug for use in patients.

Clinical testing in the development of a drug involves multiple phases. Each has standard parameters and specific requirements that must be met before a drug can advance to the next stage. The progression is generally as follows:

  • Preclinical or nonclinical testing: Laboratory and animal studies are used to determine a drug’s antibacterial activity under experimental conditions, its efficacy in animal models, and whether the drug candidate may be safe enough to test in people. Before clinical trials can begin, drug developers must file an investigational new drug application with FDA based on preclinical information that supports testing the drug candidate in humans.
  • Phase 1: The drug or treatment is tested in a small group of healthy volunteers (20 to 80) to evaluate whether it is sufficiently safe. During this phase, developers examine how the drug is absorbed and metabolized.
  • Phase 2: A drug candidate’s effectiveness and safety are evaluated in a group of patients (generally 30 to 300) who have the condition the drug is meant to treat. Developers examine the side effects and potential risks of the drug and the initial indications of its effectiveness. Phase 2 studies provide information on the drug’s optimal dose and how it should be administered.
  • Phase 3: The drug is tested in a large group (often 1,000 or more people) to gather statistically significant evidence about its safety, effectiveness, benefits, and risks. Test subjects are patients with the condition the drug is meant to treat. Phase 3 studies provide key information that FDA considers in deciding whether to approve a drug for use.
  • New drug application (NDA): A drug developer’s request to FDA for approval to market a drug to patients. This application contains the results of all animal and human studies of the drug as well as information on its manufacturing. The agency reviews the application and decides whether the drug can be approved or needs additional testing.
  • Complete response letter3: If after review of the new drug application a drug is not approved, FDA issues a complete response letter, which reflects the complete review of data submitted in an original application. In the letter, the agency provides specific descriptions of deficiencies in the application and gives the drug developer an opportunity to address these issues.
  • Phase 4 (post-marketing studies): FDA sometimes requires sponsors to monitor the long-term risks and benefits of a drug after it has been approved and to make that information available to the public. In some cases, post-marketing studies focus on a subgroup of the general population that could not be adequately evaluated during clinical testing, such as pregnant women.

Drug discovery: Early laboratory research to identify or design promising compounds that could eventually become approved medicines.

Drug target: The bacterial structure that an antibiotic acts upon. For example, macrolide antibiotics bind to a specific part of the bacterial ribosome to impede the vital process of manufacturing proteins.

Gram-negative bacteria4:  Bacteria that appear pinkish or red when subjected to a laboratory staining method known as the Gram stain test, which is used to differentiate categories of bacteria. Gram-negative bacteria can readily acquire resistance to multiple drugs and easily spread resistance to other bacteria. They have a double-layered membrane and a variety of pumps that expel drugs from the cell, factors that make them particularly difficult to attack with antibiotics. Gram-negative bacteria cause a wide range of serious infections, and some have become increasingly resistant to available antibiotic treatments. Examples of important Gram-negative pathogens with known drug resistance are Escherichia coli, Neisseria gonorrhoeae, and Gram-negative ESKAPE bacteria: Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species.

Indication: The disease or condition for which a drug was approved by FDA. Antibiotics may be approved for several conditions, including urinary tract infections, bacterial pneumonia, skin infections caused by multidrug-resistant bacteria, and a variety of others. Indications are described on the drug’s label.

Nontraditional products: A wide-ranging category of antibacterial products that differs substantially from existing antibiotics in molecular structure and mechanism of action. Traditional antibiotics are generally small molecules that kill or inhibit the growth of bacteria directly. Nontraditional products affect bacteria through alternative approaches.

  • Antibody: Proteins naturally produced by the immune system to identify and help remove potentially harmful pathogens. Novel therapies may take advantage of the specific targeting capacities that antibodies have to bind to bacteria and inactivate them in a variety of ways.
  • Live biotherapeutic product (LBP): Live microorganisms that help maintain and restore populations of beneficial bacteria in the human gut. The administration of broad-spectrum antibiotics often indiscriminately kills gut bacteria, increasing the possibility of side effects and colonization by harmful bacteria. Administering LBPs alongside antibiotics may help alleviate these risks. In addition, LBPs may help in the treatment of challenging infections such as Clostridioides difficile.
  • Lysin: Derived from bacteriophages (viruses that infect bacteria) that target and break up bacterial cell wall architecture.
  • Peptide immunomodulator: Part of most organisms’ innate immune response. They modulate the immune system to enhance its response to infection.
  • Virulence inhibitor: Molecules that work by disarming pathogens, preventing and neutralizing their harmful effects (such as bacterial toxins), or weakening bacterial defenses to help patients’ immune systems overcome infections.
  • Vaccine: Agents that stimulate the body’s immune system to recognize and destroy pathogens, such as bacteria, protecting the patient from infection. Vaccines typically contain inactivated disease-causing pathogens or components that resemble them.

Qualified infectious disease product (QIDP): Under the Generating Antibiotic Incentives Now (GAIN) Act signed into law in 2012, drug developers may request that FDA grant a QIDP designation to “an antibacterial or antifungal drug for human use intended to treat serious or life-threatening infections.” Antibiotics designated as QIDPs are eligible for incentives, including faster FDA review and, if they are approved for patients, an additional period during which they are free from generic competition.

  1. National Institutes of Health, “NIH Clinical Research Trials and You,” accessed Sept. 19, 2016,
  2. U.S. Food and Drug Administration, “FDA Drug Approval Process Infographic,” accessed Sept. 19, 2016,; U.S. Food and Drug Administration, “The FDA's Drug Review Process: Ensuring Drugs Are Safe and Effective,” accessed Sept. 19, 2016, consumers/ucm143534.htm; PhRMA, “Biopharmaceutical Research & Development: The Process Behind New Medicines,” accessed Sept. 19, 2016,
  3. U.S. Food and Drug Administration, “Applications for FDA Approval to Market a New Drug,” 21 C.F.R. § 314.110,
  4. National Institute of Allergy and Infectious Diseases, “Gram-Negative Bacteria,” accessed Sept. 19, 2016,


Antibiotic Development
Antibiotic Development

Tracking the Pipeline of Antibiotics in Development

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This collection page was updated in December 2017 with new content. Drug-resistant bacteria, or superbugs, present a serious and worsening threat to human health. A majority of doctors have encountered patients with infections that do not respond to available treatments, and when new drugs come to market bacteria can quickly develop resistance. According to a report from the Centers for Disease Control and Prevention, 2 million Americans acquire serious infections caused by antibiotic-resistant bacteria each year, and at least 23,000 die as a result. A sustained and robust pipeline of new antibacterial drugs and novel therapies is critical to ensure that new interventions keep pace with these evolving pathogens.