Therapeutic Drug Monitoring (TDM)
Facilitates the prevention and detection of therapeutic failure and toxicity.
TDM involves the measurement and interpretation of drug concentrations.
Measuring drug concentrations
- Accurate recording of drug doses and times of administration is necessary to interpret results. Put details in request form.
- Timing of samples:
- Take trough plasma samples (just before next dose) at steady state where possible.
- Patients presenting acutely are often not at steady state.
- If toxicity is suspected, take samples as required.
- Some drugs, such as aminoglycosides, require peak and trough samples.
- Ensure you use the correct tube (see below).
Interpreting drug concentrations
- Routine TDM support is provided through the ward/clinical pharmacists and the Medicines Information Service (
80900).- For aminoglycoside and vancomycin TDM, see specific guidance.
- For immunosuppressants in transplant, contact the relevant transplant team.
- For other advice on TDM or interpretation of results:
- During work hours: Clinical Pharmacology registrar (pager 8524)
- After hours: on-call General Medical ward registrar
- Key resources:
Topic Code: 93303
