Trough drug levels are best described as which of the following statements?

Trough drug levels are best described as which of the following statements?

• A. They are drawn during the absorption phase.
• B. They reflect the peak serum concentration.
• C. They are drawn just before the next dose.
• D. They are measured in urine.

Answer: (C)

Trough levels measure the lowest concentration of a drug in the bloodstream within a dosing interval. They are drawn just before the next dose is given, capturing the minimum exposure at steady state. This timing helps ensure the drug remains within the therapeutic window and avoids toxicity, especially for medications with a narrow therapeutic index. Troughs are a serum (not urine) measurement, and they are different from peak levels, which occur after dosing when the concentration is highest.

Trough levels measure the lowest concentration of a drug in the bloodstream within a dosing interval. They are drawn just before the next dose is given, capturing the minimum exposure at steady state. This timing helps ensure the drug remains within the therapeutic window and avoids toxicity, especially for medications with a narrow therapeutic index. Troughs are a serum (not urine) measurement, and they are different from peak levels, which occur after dosing when the concentration is highest.