Therapeutic drug monitoring (TDM) is the clinical practice of measuring specific drug at designated intervals to maintain a constant concentration in a patients blood stream, thereby optimizing individual dosage regimen.

1. THERAPEUTIC
DRUG
MONITORING

2. INTRODUCTION
• Therapeutic drug monitoring (TDM) is the clinical
practice of measuring specific drug at designated
intervals to maintain a constant concentration in a
patients blood stream, thereby optimizing individual
dosage regimen.
• In other words, TDM refers to the individualization
of drug dosage by maintaining plasma or blood
concentration within a targeted therapeutic range or
window.
• The goal of this process is to individualization of
therapeutic regimen for optimal patient benefits.

3. • TDM is based on the principle that for some drugs
there is a close relationship between the plasma
level of the drug and its clinical effect
• TDM aims to promote optimum drug treatment by
maintaining serum drug concentration within a
therapeutic range.

4. THE TDM PROCESS
 Decision to request drug level
 Biological samples
 The request
 Laboratory measurement
 Result communication by laboratory
 Clinical interpretation
 Therapeutic management

5. NEED FOR TDM
 To assist the optimization of drug therapy, including
minimizing the risk of serious drug toxicity.
 To identify a drug or substance which may be
contributing to the presentation of a medical
emergency.
 It is performed for the drug with narrow therapeutic
index, where small change in dose of efficiency or
toxicity.
 Useful in the patient with bipolar disorder receiving
lithium who continuous to have a symptoms of
mania.

6.  Used to assess the appropriateness of the dosing
regimen to maintain this minimum concentration &
also used to minimize the time period needed for
dosage adjustment.

7. THE BIOLOGICAL SAMPLE
 Once a decision has been made to perform TDM, it is
necessary to obtain blood sample or biological fluid
sample due to which meaningful interpretation of drug
concentration result achieved.
 Blood sample should be taken once steady- state drug
concentration have been achieved i.e., after at least 5
half-lives.
 Usually blood sample are collected at the end of
dosage interval and immediately before the next dose.
 For drugs with long half lives samples can be collected
at any time once the distribution phase is over.

8. THE MANAGEMENT OF THERAPY USING
PLASMA CONCENTRATION
Request to
laboratory
Analysis
Report
Record Previous
Results
Quality
Assessment
Interpretation Clinical
Action

9. FACTORS TO BE CONSIDERED DURING TDM
 Patient’s demographic
 Dosage regimen and duration of therapy
 Pathologic factors
 Alcohol and tobacco use
 Medicine or sampling errors
 Laboratory errors
 Sampling time
 Patient compliance
 Individual capacity to distribute, metabolise and
discrete the drug
 Altered protein binding

10.  PATIENT’S DEMOGRAPHIC: It includes patient’s
information, patient age, indication for TDM, precipitation,
etiology, past, present or future treatment, and
investigation.
 DOSAGE REGIMEN AND DURATION OF THERAPY:
Sufficient time should elapse to allow steady state to be
achieved before TDM is performed. If a loading dose has
not be given, this means at least 5 half lives of the drug
should elapse.
 PATHOLOGIC FACTORS: The patient’s comorbidities
should be taken into consideration when interpretation of
TDM results. Condition such as vomiting, diarrhoea,
inflammatory bowl disease.
 ALCOHOL AND TOBACCO USE: Chronic use of alcohol
ha been shown to cause non specific hepatic microsomal
enzyme induction, resulting in increased clearance and
decreased serum concentration of hepatically cleared
drugs such as phenytoin.

11.  MEDICINE OR SAMPLING ERRORS: In cases
where TDM result is incompatible with drug
administration records, the possibility of medication
or sampling error should be considered.
 LABORATORY ERRORS: If laboratory error
should be suspected, the laboratory should be
contacted and asked to repeat the assay.
 SAMPLING TIME: The serum concentration of
drug depends on time when the blood drawn for a
TDM assay was sampled in a relation to the last
dose.
 PATIENT COMPLIANCE: If the concentration of
drug is lower than expected, the possibilities of non
compliance should be considered.

12.  INDIVIDUAL CAPACITY TO DISTRIBUTE,
METABOLISE AND DISCRETE THE DRUG:
Patient with renal impairment have a reduced
ability to excrete renally cleared drugs & the
interpretation of TDM for renally cleared drugs
should always be made in context.
 ALTERED PROTEIN BINDING: For drugs which
are strongly bound to plasma protein, a reduced
level of albumin may result in higher concentration
of unbound drug.