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.
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:
DOSE → ADME → RECEPTOR INTERACTION AND RECEPTOR RESPONSE → CLINICAL EFFECTS
↑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
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Categories of drugs which required therapeutic drug monitoring
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| Drug category | Drugs in the category | Treatment used |
| Antiarrhythmic | Procainamide | Arrhythmia |
| Antibiotics | Aminoglycoside, gentamycin, tobramycin, netilmicin (peak>5)
Vancomycin (peak 20-40) Chloramphenicol |
Bacterial infection |
| Antiepileptics | Phenobarbital
Phenytoin Valproic acid Ethosuximide |
Epilepsy
Prevention of seizures |
| Bronchodilators
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Theophylline | Asthma, COPD, neonatal apnea, |
| Imunosupperasants | Cyclosporine
Tacrolimus |
Prevention rejection of transplanted organs |
| Anticancer drugsq\ | Methotrexate | Cancer
Rheumatic arthritis |
| Psychiatric disease | Lithium, desipramine,
Imipramine Amytriptaline
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Bipolar disorder
Manic depression |
