ABSTRACT
Therapeutic drug monitoring (TDM) is a concept that utilizes the drug concentration measurement in biological ¥uids as a tool for individualization of drug therapy and dosage adjustment. This concept is based on the strong correlation observed between the drug concentration in the systemic circulation and the therapeutic as well as toxic effects for many drugs. This strong correlation indicates that most drugs exert their desired therapeutic effects with minimal adverse effects in the majority of patients when their blood or plasma concentrations are maintained within a certain concentration range, which is known as the therapeutic range. The drug concentration achieved at steady state in a particular patient is dependent on the dosing rate of the drug and the drug total body clearance in this particular patient. When the same dose of a drug is administered to a group of patients, different drug concentrations are achieved in different patients due to many factors related to the drug product and the patient-specic characteristics. This explains why the correlation between the blood drug concentration and effect is stronger than the correlation between the drug dose and effect.
