Drug resistance

Drug resistance is the reduced effectiveness of a medicine against a disease because biological or environmental changes make treatment less effective.

Target-site modification: A change to a drug’s binding site that reduces the drug’s ability to act. Pathogens and cancer cells can alter drug targets while preserving their essential function.
Natural selection: The change in inherited trait frequencies when individuals differ in survival or reproduction. Drug exposure favors organisms that already carry traits allowing survival.
Antimicrobial susceptibility testing: Laboratory methods that determine whether a microorganism is inhibited by particular antimicrobial drugs. Testing helps identify which medicines remain active against an infection.
Treatment failure: The inability of a treatment to achieve its intended clinical outcome. Resistance can allow disease to persist or progress despite an apparently appropriate medicine.
Drug susceptibility: The degree to which an organism or disease responds to a particular medicine. It is the counterpart to resistance: susceptible pathogens remain inhibited by the drug.
Drug efflux: The active transport of a substance out of a cell. Efflux pumps lower intracellular drug concentrations before medicines can act.
Mutation: A change in the DNA sequence of an organism. Random mutations can alter drug targets or other traits that affect susceptibility.
Minimum inhibitory concentration: The lowest concentration of an antimicrobial that visibly inhibits microbial growth under defined test conditions. MIC measurements help classify isolates and guide antimicrobial treatment.
Multidrug resistance: Resistance to multiple drugs, often from different classes, in an organism or disease. Resistance to several drug classes can sharply narrow available treatment options.
Antibiotic tolerance: The ability of a microbial population to survive longer exposure to an antibiotic without a higher minimum inhibitory concentration. Tolerance prolongs survival without necessarily increasing the concentration needed to stop growth.

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