Therapeutic drug monitoring

Therapeutic drug monitoring


       Need for therapeutic drug monitoring

       Importance of TDM


After completion of this lecture, student will be able to:

       To study in detail about therapeutic drug monitoring

       To know the importance of TDM


       Therapeutic drug monitoring (TDM) involves tailoring a dose regimen to an individual patient, by maintaining plasma or blood concentrations with a therapeutic range

Why should drug levels be monitored?

       Certain drugs have a narrow therapeutic range

       In concentrations above the upper limit of the range, the drug can be toxic

       In concentrations below the lower limit  of the range, the drug can be ineffective

       Not all patients have the same response at similar doses

Conditions in which TDM will be useful

       The drug in question has a narrow therapeutic range

       A direct relationship exists between the drug or drug metabolite levels in plasma and the pharmacological or toxic effects

       The therapeutic effects cannot be readily  assessed by the clinical observations

       Large individual variability in steady state plasma concentrations exists at any given dose

       Appropriate analytical techniques are available to determine the drug or metabolite levels

Conditions in which TDM is unnecessary

       Clinical outcome is unrelated either to dose or to plasma concentration

       Dose need not be individualized

       Pharmacological effects can be clinically quantified

       When concentration effect relationship remains unestablished

       Drugs with wide therapeutic range

TDM indications for drugs

       Low therapeutic index

       Poorly defined clinical end point

       Non compliance

       Therapeutic failure

       Drugs with saturable metabolism

       Wide variation in the metabolism of drugs

       Major organ failure

Applicability of therapeutic ranges

       Therapeutic ranges are recommendations derived by observing the clinical reactions of a small group of patients taking the drug

       The lower limit (trough) is set to provide 50% of the maximum therapeutic effects while upper limit (peak) is defined by toxicity

       Some patients may achieve therapeutic effects at levels below the established range, while some may experience toxicity in the established range

Factors that affects the results




       Sampling time and type

       Testing methodology

       Genetic polymorphisms

Sources of pharmacokinetic variability

       Patient compliance



       Disease conditions

       Drug- drug interactions

       Environmental influences

Sampling time

       The drug concentrations varies over the entire dosing interval and with the duration of dosing in relation to achieve a steady state

       Drugs with short half-lives , in relation to the dosing interval, requires trough concentration monitoring

       Drugs with long half-lives can be monitored  at any point in the dosing interval

Other factors

       Some anti-coagulants may interfere with results for certain drugs. Ex. Heparin affects lithium results

       Some gel separators interfere with the results of certain drugs

       Sensitivity and specificity of the testing methodology

Interpretation of TDM values

       Measuring the blood concentration of certain drugs is one aspect of TDM monitoring

       Therapeutic ranges are available but should be used only as a guide. It must always be interpreted in the context of clinical data

       Many factors alter the effect of a drug concentration at a site of action

Factors that affect interpretation

       Protein binding

       Active metabolites

       Steady state

       Turnaround time

Sample Information Required For Accurate Interpretation

       Time of sample in relation to the last dose

       Duration of treatment with the current dose

       Dosing schedule

       Age, gender

       Other drug therapy

       Disease states

Testing methods

       HPLC- high pressure liquid chromatography

       GC/MS- gas chromatography mass spectrophotometry

       LC/MS- liquid chromatography mass spectrometry

       RIA- radio immune assay

       PETINIA- particle enhanced turbidimetric inhibition immuoassay

       EIA- enzyme immune assay

       EMIT- enzyme multiplied immunoassay technique

       FPIA- fluorescence polarization immunoassay


       ACMIA- affinity chrome- mediated immunoassay

       CEDIA- cloned enzyme donor immunoassay

Commonly Monitored Drugs


       Anti- arrythmic






       Therapeutic drug monitoring (TDM) involves tailoring a dose regimen to an individual patient, by maintaining plasma

       Condition in which TDM should be monitored

       Factors affecting TDM

       Testing Methods

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