Therapeutic Drug Monitoring
- Also Known As:
- TDM

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What is therapeutic drug monitoring (TDM)?
Therapeutic drug monitoring is the measurement of specific drugs and/or their breakdown products (metabolites) at timed intervals to maintain a relatively constant concentration of the medication in the blood. Some of the monitored drugs tend to have a narrow “therapeutic index,” which is a ratio between the toxic and therapeutic (effective) dose of medication.
As soon as a drug enters the body, different processes start removing the drug from the body. The amount of time it takes for the body to reduce the drug concentration to half from the initial value is called a half-life of the drug. It generally takes around five half-lives to remove a drug completely from the body.
Generally, a person must be given a drug dose at regular intervals to ensure that the effective or the therapeutic concentration of the drug is maintained in the body. For some drugs, maintaining this steady state is not as simple as giving a standard dose of medication. Each person will absorb, metabolize, utilize and eliminate drugs at different rates based upon their age, general state of health and genetic makeup. The drug concentration in the body may be enhanced or decreased by the interference of other medications that you may be taking along with the drug which has to be motioned. This is also known as drug-drug interaction.
Not all medications require therapeutic monitoring. Most drugs have a wide therapeutic index and can be prescribed based upon pre-established dosing schedules. The effectiveness of these treatments has been evaluated, but monitoring the concentration of the drug in the blood is not required for dosing. Examples of drugs that do not require monitoring include high blood pressure (hypertension) medications and many of the antibiotics given to treat bacterial infections. If an infection resolves with a given antibiotic or if blood pressure is lowered with the prescribed blood pressure medication, then the treatments have been effective.
Common Questions
Monitored Drugs by Category
Drug Category | Drugs | Treatment Use |
---|---|---|
Cardiac drugs | Digoxin, digitoxin, amiodarone, lidocane, quinidine, procainamide, N-acetyl-procainamide (a metabolite of procainamide) | Congestive heart failure, angina, arrhythmias |
Antibiotics | Aminoglycosides (gentamicin, tobramycin, amikacin), vancomycin, chloramphenicol | Infections with bacteria that are resistant to less toxic antibiotics |
Antiepileptics | Phenobarbital, phenytoin, valproic acid, carbamazepine, ethosuximide, sometimes gabapentin, lamotrigine, levetiracetam, topiramate, zonisamide, eslicarbazepine acetate, felbamate, lacosamide, oxcarbazepine, pregabalin, rufinamide, stiripentol, tiagabine, vigabatrin | Epilepsy, prevention of seizures, sometimes to stabilize moods |
Bronchodilators | Theophylline, caffeine | Asthma, chronic obstructive pulmonary disorder (COPD), neonatal apnea |
Immunosuppressants | Cyclosporine, tacrolimus, sirolimus, mycophenolate mofetil, azathioprine | Prevent rejection of transplanted organs, autoimmune disorders |
Anti-cancer drugs | Methotrexate, all cytotoxic agents | Psoriasis, rheumatoid arthritis, various cancers, non-hodgkin lymphomas, osteosarcoma |
Psychiatric drugs | Lithium, valproic acid, some antidepressants (imipramine, amitriptyline, nortriptyline, doxepin, desipramine) | Bipolar disorder (manic depression), depression |
View Sources
Sources Used in Current Review
2018 review completed by Jasbir Singh Arora, PhD, NRCC.
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Sources Used in Previous Reviews
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