Therapeutic drug monitoring


Therapeutic drug monitoring

TDM evolved out of a need to optimize & individualize drug therapy. It is based on the pharmacokinetic and utilizes drug concentration in the body fluids as a guide to the individualize dosage form.

There is an excellent correlation between plasma concentration of a drug and the response it produces, the aim is  to maintain plasma concentration within the therapeutic range as to maximize the therapeutic benefit which id minimal adverse affect

It is usually indicated for large no of drugs especially those showing a narrow therapeutic range, wide individual variation multiple drug interactions example Aminoglycoside, Antiarrhythmics, Antiepileptics, Antidepressants, Digoxin, Theophylline etc.

Plasma or Serum
Plasma or Serum

What is Therapeutic drug monitoring?

TDM can be defined as a pragmatic manipulation of the dose of a drug using plasma level as a guide to optimize its efficacy to avoid or identify toxicity and to detect or confirm.

It is a therapy involves administration of potent medication to a patient during administration of dosage form the concentration is maintained between maximum and minimum effective concentration that is minimum effective concentration and maximum safe concentration within the therapeutic window in the case of a potent drug.

Why Is TDM needed?

Everybody is unique some people so as there pharmacokinetic effects of drugs are also different and these are called variability there are basically two types of variability

  • Pharmacokinetic  variability- Dose and plasma concentration variability
  • Pharmacodynamic variability- Drug concentration at the receptor and the response

sources of pharmacodynamic and pharmacokinetic variability:


Pharmacokinetic phase of drug interaction                     ↑  Pharmacodynamic phase of drug interaction

  • Age                                                                                                  Receptor interaction
  • Physiology                                                                                       Receptor response
  • Disease states                                                                                 Drug interaction
  • Tissue, body fluid and mass                                                            Genetic factor
  • Compliance                                                                                     Tolerance
  • Drug interaction
  • Environmental factor influencing metabolism
  • Genetical polymorphism in drug metabolism

Which drugs require monitoring?

  • Drugs which have defined therapeutic concentration range
  • Drugs in which desired therapeutic effect is very difficult to detect
  • Drugs that shows marked pharmacokinetic variability
  • Drugs who have concentration related therapeutic and adverse effect
  • Drugs who have narrow therapeutic index



Categories of drugs which required therapeutic drug monitoring


Drug category Drugs in the category Treatment used
Antiarrhythmic Procainamide Arrhythmia
Antibiotics Aminoglycoside, gentamycin, tobramycin, netilmicin (peak>5)

Vancomycin (peak 20-40)


Bacterial infection
Antiepileptics Phenobarbital


Valproic acid



Prevention of seizures



Theophylline Asthma, COPD, neonatal apnea,
Imunosupperasants Cyclosporine


Prevention rejection of transplanted organs
Anticancer drugsq\ Methotrexate Cancer

Rheumatic arthritis

Psychiatric disease Lithium, desipramine,




Bipolar disorder

Manic depression