Importance and Methods of Therapeutic Drug Monitoring

In this article, we will discuss the importance and methods involved in Therapeutic Drug Monitoring (TDM). As we know that Therapeutic Drug Monitoring is a branch of clinical chemistry and clinical pharmacology as discussed in the previous tutorial overview and steps involved in TDM.

Importance of Therapeutic Drug Monitoring

The importance of Therapeutic Drug Monitoring is the following:

  •  Accurate dispensing of the drug.
  •  Record accurate time for drug administration.
  •  No medication error.
  • Giving the correct dose of the drug.
  • Drawing the blood at the correct time and from correct site.
  • Accurate lab assay procedure.

Methods of Therapeutic Drug Monitoring

These methods are used for estimation of the drug in a TDM laboratory can be classified into:

1. Chromatographic Methods- HPLC, Gas chromatography measure and identify several drugs and their metabolite in one run. These are cheaper but lengthy procedure and technically demanding.

2. Immunological Methods- You can use the followings for immunological:

  • Like enzyme immunoassay(EIA)
  • Enzyme-linked immunosorbent assay (ELISA)- used for Theophylline
  • Enzyme multiplied immunoassay Technique(EMIT)- used for Phenytoin, Gentaycine
  • Solid Phase Enzyme Immuno Assay(SPEA)- used for Carbanazepine
  • Radial Partition Immunoassay(RPIA)- used for phenobarbitone
  • Florescene Polarization Immuno Assay(FPIA)- used for Digoxine, Primidone
  • Substrate linked Florescene ImmunoAssay(SLFIA)- used for Tobramycine

2.1 Immunoassay divided into two type-

Heterogeneous ImmunoassayHomogenous Immunoassay
Bound tracer separated from unbound in order to be measuredNo separation is necessary
A higher degree of sensitivityLess sensitivity
Minimize non-specific interferenceHigh interference due to the biological fluid
Uniquely suitable for TDM since the drug is not normally present in body fluid ac be obtained from in large quantitiesSame as Heterogeneous

Need of Therapeutic Drug Monitoring

TDM is necessary when-

  • Patient undergoing dialysis, haemofiltration, burn therapy.
  •  Suspected malabsorption.
  • Renal and hepatic impairment, cardiac dysfunction, cystic fibrosis.
  • Polypharmacy therapy.
  •  Drug as prophylactic.
  • The poor relationship between dose and blood level.
  • Low therapeutic index (TI).
  •  High adverse effect.
  •  Clinical and pharmacological response not measured easily and accurately or one or more condition.


  1. Overview of Therapeutic Drug Monitoring
  2. Therapeutic drug monitoring- Wiki

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Ankita Rai
Hey, I'm graduated in Pharmacy and working with a top reputed company as quality control and analysis. I love to share my ideas, and knowledge with everyone by writing articles on the latest pharmacy trends and thanks to Websparrow team to provide me a platform. Read all published posts by Ankita Rai.