Therapeutic drug monitoring (TDM) involves measuring drug levels in a patient's bloodstream to maintain an optimal concentration range. It is important because the effects of drugs can vary between patients due to differences in pharmacokinetic parameters like bioavailability. TDM allows for individualized dosing by considering a patient's serum drug concentrations, pharmacokinetics, pharmacodynamics, and maintaining therapeutic levels. Key parameters monitored in TDM include drug clearance, concentrations, half-life, and timing of administration.
2. THERAPEUTIC DRUG MONITORING (TDM)
The action of a drug varies from patient to patient
Thus the pharmacodynamic effects of drugs depends on
the pharmacokinetic parameters and Pharmacokinetic
parameters vary from person to person and thus the
bioavailability of drug varies
TDM refers to the individualization of dosage by using
the serum drug concentrations (SDCs), pharmacokinetic,
and pharmacodynamic data and maintaining plasma or
blood drug concentration within a target range
It is the measurement of specific drugs at intervals in
order to maintain a relatively constant concentration in
the bloodstream.
It is a practice applied to drugs, which has a direct
correlation between SDCs and narrow therapeutic index
3. Importance of Therapeutic Drug Monitoring
The importance of Therapeutic Drug Monitoring is the
following:
for treatment as well as for diagnostic purposes
helps in designing patient-specific dosage regimen
to reduce the toxicity of drug
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.
4. Parameters used to monitor TDM
These are:
Drug clearance
Maximum concentration
Minimum concentration
Half life
Onset of action
Duration of action
Time to reach maximum concentration
Average concentration resulting from intermittent
administration
Steady state concentration from continuous
administration Important facts
5. Information Required for TDM
Pharmacokinetics of the drug
Patient’s clinical condition
Patient’s clinical history concerning past therapeutic
responses
Dosage regimen
Sampling time
Purpose of therapeutic drug monitoring, i.e. whether to
determine efficacy, toxicity or for diagnostic purpose
Patient’s clinical responses
6.
7. Timing of specimen collection
The specimen should be collected after the absorption
and distribution phases are complete and steady-state
has been achieved,
Drug levels obtained before steady state has been
achieved could be interpreted improperly as being sub-
therapeutic and prompt an increase in dose,
for half-lives drugs, such as the Aminoglycosides, both a
steady-state, peak and trough level should be obtained,
Trough levels are collected just prior to the next dose,
Drugs with a long half-life, steady-state trough levels
provide sufficient clinical information.
