What is therapeutic drug monitoring (TDM) and provide an example of a drug typically monitored this way?

• A. Measuring drug concentrations to optimize therapy; example: vancomycin trough levels, or aminoglycoside levels
• B. Predicting patient response via genetics
• C. Monitoring only liver enzymes
• D. Checking electrolytes

Answer: (A)

Therapeutic drug monitoring is measuring a drug’s concentration in the blood to keep its level within a range that is effective but not toxic. This is especially important for medicines with a narrow therapeutic index and highly variable pharmacokinetics, where small differences between patients can lead to underdosing or toxicity.

Vancomycin is a classic example. Clinicians often check trough levels (the concentration just before the next dose) to guide dosing and ensure adequate exposure while avoiding nephrotoxicity. Aminoglycosides, such as gentamicin or tobramycin, are another common instance where blood concentration checks help balance bacterial killing with risks of kidney and ear toxicity. In practice, these measurements inform dose adjustments and, for some drugs, dosing strategies that optimize exposure (and sometimes target specific pharmacodynamic goals like AUC).

Other options don’t fit this concept because they describe different kinds of monitoring. Predicting patient response via genetics refers to pharmacogenomics, not measuring drug levels. Monitoring liver enzymes or checking electrolytes involves organ function or general labs, not drug concentrations for dose optimization.