Trough levels are measured just before the next dose.

• A. Just Before the Next Dose
• B. Immediately Before the Next Dose
• C. Fifteen Minutes After the Dose
• D. At the Time of the Next Dose

Answer: (A)

The main idea is that a trough level shows the drug’s lowest concentration in the body between doses, so it must be measured just before the next dose is given. This timing captures the point where the drug level has fallen to its minimum before re-administration, which is exactly what clinicians use to ensure the dose keeps the level therapeutic without dipping too low. If you sample after dosing, you’d be measuring a higher concentration as the drug is absorbed and distributed, which reflects the peak or rising levels rather than the trough. Sampling at the exact moment the next dose is due can be ambiguous, whereas “just before the next dose” clearly targets that lowest concentration right before re-dosing.