• Diminished or failed response of an organism, disease or tissue to the intended effectiveness of a chemical or drug. It should be differentiated from DRUG TOLERANCE which is the progressive diminution of the susceptibility of a human or animal to the effects of a drug, as a result of continued administration.
  NLM Medical Subject Headings
  U.S. National Library of Medicine, 2021
• Tendency of biological systems (organisms, cells, or cell-free systems) to fail to respond as expected to drug treatment or exposure; may be due to specific enzymes, transporters, or receptors which block drug action.
  CRISP Thesaurus
  National Institutes of Health, 2006
• The failure of cancer cells, viruses, or bacteria to respond to a drug used to kill or weaken them. The cells, viruses, or bacteria may be resistant to the drug at the beginning of treatment, or may become resistant after being exposed to the drug.
  NCI Dictionary of Cancer Terms
  U.S. National Cancer Institute, 2021
• (drug resistance process) Mechanisms, functions, activities, or processes exhibited by tumors or pathogens to withstand previously toxic drugs.
  NCI Thesaurus
  U.S. National Cancer Institute, 2021
• (refractory drug response) Absent or significantly reduced efficacy of drug intervention characterized by lack of measurable benefit or deterioration of disease course.
  Human Phenotype Ontology (HPO)
  The Human Phenotype Ontology Project, 2021