Therapeutic window

The concentration range for a drug in an individual that lies above the “minimum effective concentration” (MEC) and below the “maximum tolerated concentration” (MTC). It is the range within which the drug’s steady state concentration, that will be reached with chronic dosing, must lie in order to treat the patient effectively, while avoiding serious side-effects. The smaller a drug’s therapeutic window, quantified by a value for the drug’s therapeutic index, the greater the need to customise a dosing regimen to an individual patient in order to minimise the risk of side effects.