Therapeutic drug monitoring

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Therapeutic drug monitoring (TDM) is a branch of clinical chemistry and clinical pharmacology that specializes in the measurement of medication concentrations in blood. Its main focus is on drugs with a narrow therapeutic range, i.e. drugs that can easily be under- or overdosed.[1] TDM aims at improving patient care by individually adjusting the dose of drugs for which clinical experience or clinical trials have shown it improved outcome in the general or special populations. It can be based on a priori pharmacogenetic, demographic and clinical information, and/or on the a posteriori measurement of blood concentrations of drugs (pharmacokinetic monitoring) or biological surrogate or end-point markers of effect (pharmacodynamic monitoring).[2]

There are numerous variables that influence the interpretation of drug concentration data: time, route and dose of drug given, time of blood sampling, handling and storage conditions, precision and accuracy of the analytical method, validity of pharmacokinetic models and assumptions, co-medications and, last but not least, clinical status of the patient (i.e. disease, renal/hepatic status, biologic tolerance to drug therapy, etc.).[3]

Many different professionals (physicians, clinical pharmacologists, clinical pharmacists, nurses, medical laboratory scientists, etc.) are involved with the various elements of drug concentration monitoring, which is a truly multidisciplinary process. Because failure to properly carry out any one of the components can severely affect the usefulness of using drug concentrations to optimize therapy, an organized approach to the overall process is critical.[3]

A priori therapeutic drug monitoring[edit]

A posteriori therapeutic drug monitoring[edit]

Characteristics of drugs subject to therapeutic drug monitoring[edit]

In pharmacotherapy, many medications are used without monitoring of blood levels, as their dosage can generally be varied according to the clinical response that a patient gets to that substance. In a small group of drugs, this is impossible, as insufficient levels will lead to undertreatment or resistance, and excessive levels can lead to toxicity and tissue damage.

Indications for therapeutic drug monitoring include:

  • There is an experimentally determined relationship between plasma drug concentration and the pharmacological effect.
  • Knowledge of the drug level influences management.
  • There is a narrow therapeutic window
  • There are potential patient compliance problems.
  • The drug dose cannot be optimised by clinical observation alone.

Examples of drugs analysed by therapeutic drug monitoring:[1]

Therapeutic drug monitoring can also detect poisoning with above drugs, should the suspicion arise.


  1. ^ a b Marshall WJ, Bangert SK. Clinical Chemistry, 6th Edition. Edinburgh, London: Mosby Elsevier. 2008. ISBN 978-0-7234-3455-9
  2. ^ a b c IATDMCT Executive Committee. "Definition of TDM", 2004, accessed July 18, 2011. Cite error: Invalid <ref> tag; name "Definition_of_TDM" defined multiple times with different content (see the help page). Cite error: Invalid <ref> tag; name "Definition_of_TDM" defined multiple times with different content (see the help page).
  3. ^ a b Burton ME, Shaw LM, Schentag JJ, Evans, WE. Applied Pharmacokinetics & Pharmacodynamics, 4th Edition. Baltimore, Philadelphia: Lippincott Williams & Wilkins. 2006. ISBN 978-0-7817-4431-7

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