Therapeutic Drug Monitoring (TDM)

Therapeutic Drug Monitoring (TDM)

The Programme aims to assess the performance of organisations utilising biochemical assays to aid in the management of patients on certain therapeutic drugs.

Drugs with a narrow Therapeutic index (difference between therapeutic concentration and toxic concentration) need to be monitored and controlled, as levels too high or low in the serum can result in adverse effects associated with toxic or fatal outcomes. The indications for drug monitoring have widened to include efficacy, compliance, drug-drug interactions, toxicity avoidance, and therapy cessation monitoring. These include certain antibiotics, antiepileptic drugs, digoxin, psychiatrics, and immunosuppressant drugs.

TDM are most commonly tested with serum or plasma using commercially available immunoassays. While convenient and cost-effective, some assay interferences have been observed due to cross-reactivity with the drug’s metabolites, and in some cases, endogenous compounds or drugs with similar structures.

Separate samples are provided in Whole Blood for the Immunosuppressant drugs: Ciclosporin, Sirolimus and Tacrolimus.

Three liquid human serum samples and three whole blood samples are distributed monthly, with a minimum of 36 samples of each type distributed over the year covering the therapeutic and/ or toxic range. The base material is “off the clot” sterile human serum or whole blood, tested negative for HIV, Hep B and C at donor level. Each therapeutic drug is gravimetrically added; the “weighed-in” value and its known linear dilution is then used to calculate the target concentration. A linear series of pools are prepared using calibrated and certified equipment allowing full gravimetric traceability.

The panels are distributed on a number of occasions over a year which allows for the assessment of the organisation’s and method’s performance, including sensitivity, specificity, linearity (recovery to gravimetric), bias, within and between batch imprecision.

Key Features:

  • Stable liquid human serum samples or whole blood requiring no pre-analytical preparation.
  • Linear panel with known traceable “gravimetric, weighed in” concentration of drug.
  • Programme assesses both laboratory and method performance, including, sensitivity, specificity, linearity (recovery to gravimetric), bias, within and between batch imprecision.
  • Clinically relevant concentration range at therapeutic and toxic concentrations.

3 x 1.0mL
Off the clot human serum and whole blood
Therapeutic Drug Monitoring (TDM) Programme
AnalyteApprox. Range Covered
Amikacin0 - 25mg/L
Carbamazapine0 - 12mg/L
Digoxin0 - 3µg/L
Gentamicin0 - 5mg/L
Lamotrigine0 - 24mg/L
Lithium0 - 2.0mmol/L
Methotrexate0 - 1.0µmol/L
Phenobarbital0 - 40mg/L
Phenytoin0 - 25mg/L
Teicoplanin0 - 60mg/L
Theophylline0 - 20mg/L
Tobramycin0 - 10mg/L
Valproic acid0 - 125mg/L
Vancomycin0 - 30mg/L
Whole Blood Immunosuppressants
- Ciclosporin0 - 600µg/L
- Sirolimus0 - 20µg/L
- Tacrolimus0 - 15µg/L

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