Therapeutic Drug Monitoring

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The page below is a sample from the LabCE course Special Topics in Phlebotomy. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Therapeutic Drug Monitoring

Therapeutic drug monitoring helps to ensure that a dosing regimen is appropriate for a given patient. The blood plasma concentration of the drug is measured to determine the correct dose that will achieve a therapeutic level of the drug without overdosing into a toxic range. When a drug enters the body, it reaches a peak concentration that starts to fall as the drug is eliminated.
The amount of time it takes for a drug's concentration in the body to decrease by 50% is called the drug's half-life. The longer a drug's half-life, the slower it is removed from the body. Most drugs are eliminated from the body in one to three days, but some drugs with longer half-lives can still be detected in the body weeks after the initial dose.
The figure on the right illustrates a typical concentration pattern for a drug that is given orally (ingested).