Why are peak and trough concentrations monitored during therapy?

• A. To ensure concentrations stay within the therapeutic window and adjust dosing.
• B. To measure genetic factors affecting PK.
• C. To determine drug color in the formulation.
• D. To assess patient satisfaction with dosing schedule.

Answer: (A)

Monitoring peak and trough concentrations aims to keep drug exposure within a safe and effective range. The peak is the highest level after dosing, and the trough is the lowest level just before the next dose. For many drugs, especially those with a narrow therapeutic index, small changes in concentration can shift from therapeutic to toxic. By measuring these levels and comparing them to target ranges, clinicians can adjust the dose or dosing interval so the trough stays above the minimum effective concentration and the peak stays below the level that causes toxicity. This approach, therapeutic drug monitoring, accounts for individual differences in absorption, distribution, metabolism, and elimination. Factors like genetics or patient satisfaction don’t directly determine bloodstream concentrations, and drug color is irrelevant to pharmacokinetics.