Therapeutic Drug Monitoring (TDM)

Therapeutic drug monitoring (TDM) refers to the measurement and interpretation of principally blood plasma drug concentration measurements with the purpose of optimizing a patient’s drug therapy and clinical outcome while minimizing the risk of drug-induced toxicity.

TDM involves tailoring a dosing regimen to an individual patient by maintaining the plasma or blood concentration within a particular range.

To achieve optimal drug therapy 3 objectives should be met:
  1. To attain desired pharmacological effect of the drug.
  2. To reach the maximal effect in the shortest possible time.
  3. To decrease the risk of toxicity.

TDM is useful in drugs:
  1. With a narrow therapeutic index.
  2. Which is highly protein bound.
  3. Which are liable to interact?
  4. In which the metabolite might be toxic.

A reliable and responsive TDM service depends on teamwork between nurses, doctors, pharmacists, scientists, and technical staff. The clinical pharmacist should provide advice to medical staff on the appropriate use and timing of TDM and assist with the interpretation of results. 
In addition, the pharmacist may be involved in:
  1. An initial selection of drug regimen. This may involve decisions about drug choice, dose, dosing interval, route of administration and dosage form of the drug, taking into account factors such as sex, age, body weight, race, metabolism status, renal function, plasma albumin concentration, use of other drugs and laboratory results.
  2. Adjustment of the dosage regimen based on TDM results and the patient's clinical response,.
  3. Assessment of possible causes for unexpected results, such as non-compliance, bioavailability problems, medication errors, drug interactions or pharmacogenetic variability.
  4. Dose adjustment for patients on haemodialysis or peritoneal dialysis.
  5. Provision of poisons information.

  • It is a fundamental responsibility of a pharmacist to ensure the appropriateness of medication orders.
  • It serves as starting point for other clinical pharmacy activities (medication counseling, TDM, DI, and ADR).
  • Organizing information according to medical problems (example disease) helps breakdown a complex situation into its individual parts.

  1. To optimize the patient's drug therapy.
  2. To prevent or minimize drug-related problems/medication errors.

  • The patient’s medical record should be reviewed in conjugation with the medication administration record.
  • Recent consultations, treatment plans and daily progress should be taken into account when determining the appropriateness of current medication orders and planning each patient’s care.
  • All current and recent medication orders should be reviewed.


It includes:
  • Checking that medication order is written in accordance with legal and local requirements.
  • Ensuring that the medication order is comprehensible and unambiguous, that appropriate terminology is used and that drug names are not abbreviated. Annotate the chart to provide clarification as required.
  • Detecting orders for medication to which the patient may be hypersensitive/ intolerant.
  • Ensuring that medication order is appropriate with respect to:
  1. The patient’s previous medication order.
  2. Patient’s specific considerations e.g. disease state, pregnancy.
  3. Drug dose and dosage schedule, especially with respect to age, renal function, liver function.
  4. Route, dosage form and method of administration.
  • Checking complete drug profile for medication duplication, interactions or incompatibilities.
  • Ensuring that administration times are appropriate e.g. with respect to food , other drugs and procedures.
  • Checking the medication administration record to ensure that all ordered have been administered.
  • Ensuring that the drug administration order clearly indicates the time at which drug administration is to commence.
  • special considerations should be given especially in short course therapy as in antibiotics and analgesics.
  • Ensuring that the order is cancelled in all sections of medication administration record when the drug therapy is intended to cease.
  • If appropriate follow up of any non-formulary drug orders, recommending a formulary equivalent if required.
  • Ensuring appropriate therapy monitoring is implemented.
  • Ensuring that all necessary medication is ordered. E.g. premedication, and prophylaxis.
  • Reviewing medication for cost-effectiveness.
  • Identification of drug-related problems.
  1. Untreated indication.
  2. Inappropriate drug selection.
  3. Sub-therapeutic dose.
  4. Adverse drug reaction.
  5. Failure to receive drug.
  6. Drug interactions.
  7. Drug use without indication.
  8. Overdosage.

Medication chart Endorsement
  • Another important goal of treatment char review is to minimize the risk of medication errors that might occur at the level of prescribing and / or drug administration.
  • A medication error is any preventable error that may lead to inappropriate medication use or patient harm.
  • To prevent potential morbidity and mortality associated with these errors, pharmacists should systematically review the medication chart and write annotations on the chart where the medication orders are unclear.

Clinical review is one of the integral components of medication review and should preferably be performed on a daily basis. It is the review of the patients’ progress for the purpose of assessing the therapeutic outcome. The therapeutic goal for the specific disease should be clearly identified before the review.

  • The primary aims of the clinical review are to:
  • Assess the response to drug treatment.
  • Evaluate the safety of the treatment regimen.
  • Assess the progress of the disease and the need for any change in therapy.
  • Assess the need for monitoring, if any.
  • Assess the convenience of therapy (to improve compliance).

Clinical pharmacists can audit their impact on patient care by intervention monitoring. Some hospitals undertake these audits at regular intervals and present the results internally or to the multidisciplinary team. Data collection forms or electronic hand-held systems are used to collect the relevant data on a pharmacist’s interventions to improve patient care. Examples of data collected for this purpose include the following.
  1. Patient details and demographics.
  2. Area of work/specialization.
  3. Written details of the intervention.
  4. Date of intervention.
  5. Other healthcare professionals were contacted.
  6. Evidence was used to support the intervention.
  7. Who initiated the intervention — e.g. pharmacist, doctor, nurse, or patient.
  8. The possible effect the intervention would have on patient care.
  9. Outcome of the intervention.
  10. Actual outcome on patient care that the intervention had.
  11. Significance of intervention.
  12. Category of intervention.

Examples of the categories of pharmacist interventions in drug therapy:
  1. ADRs
  2. Allergy
  3. Additional drug therapy required
  4. Medication error
  5. Medication without indication
  6. Untreated condition or undertreated condition
  7. Minimal or no therapeutic effectiveness
  8. Therapeutic duplication
  9. Patient adherence, compliance, or drug administration issue
  10. Patient education
  11. Communication with prescriber
  12. Incorrect medication prescribed
  13. Inappropriate or suboptimal dose, schedule, or route
  14. Optimization of drug therapy, including improving cost-effectiveness
  15. Dose advice
  16. Advice on drug choice
  17. Drug–drug, drug–food, or drug–disease interaction
  18. Side effect/toxicity
  19. Therapeutic monitoring for toxicity or effectiveness
  20. Formulation
  21. Compatibility
  22. Formulary or protocol adherence
An example of an intervention monitoring form is shown in Table.

Significance of Intervention



Unlikely to have an effect on patient outcome


Potentially undesirable for patient outcome


Potentially Detrimental to patient outcome

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