The trough level is defined as what?

The trough level is defined as what?

• A. The highest blood level of a drug
• B. The lowest blood level of a drug
• C. The time to onset of action
• D. The therapeutic level

Answer: (B)

The trough level is the lowest drug concentration in the blood within a dosing interval, measured right before the next dose. This measurement helps confirm that levels remain above the minimum effective concentration but below toxic levels, which is crucial for drugs with narrow therapeutic windows. The highest blood level is the peak, not the trough, and the time to onset of action relates to when the drug begins to work rather than its concentration at a specific time. The therapeutic level refers to the target range overall, not specifically the lowest point in the interval.