What are sensitive, intermediate, and resistant antibiotics?
To achieve simplification a standardised, threshold based assessment scheme is used in which the degree of drug effectiveness is characterised as susceptible, intermediate or resistant.
The goal of antimicrobial susceptibility testing is to predict the in vivo success or failure of antibiotic therapy.
Susceptible (earlier sensitive): a bacterial strain is said to be susceptible to a given antibiotic, when it is inhibited in vitro by a concentration of drug that is associated with a high likelihood of therapeutic success.
Intermediate : the sensitivity of a bacterial strain to a given antibiotic is said to be intermediate when it is inhibited in vitro by a concentration of the drug that is associated with an uncertain therapeutic effect.
Resistant : a bacterial strain is said to be resistant to a given antibiotic when it is inhibited in vitro by a conc of the drug that is associated with a high likelihood of therapeutic failure.
The classification 'intermediate' means that the organism may well be eliminated in body parts that are easily accessible by the drug( e.g. Urinary tract), while the same may not be adequately effective against the same organisms, if it is located at other site ( e.g. Meningitis).
Sensitivity testing is used to determine the right antibiotic treatment for an infection and to monitor changes in bacterial resistance to antibiotics.