What is the clinical consequence of drawing a trough sample too late before the next dose?

• A. Sampling too late has no effect on interpretation.
• B. Trough sampling timing only affects documentation.
• C. Inaccurate exposure assessment leading to inappropriate dosing.
• D. It always overestimates drug exposure.

Answer: (C)

Trough level timing is crucial for estimating drug exposure over the dosing interval. If the sample is drawn too late, the drug has continued to be eliminated after the ideal trough moment, so the measured concentration is lower than the true minimum just before the next dose. This yields an artificially low assessment of overall exposure (the trough and, by extension, the calculated exposure like AUC). Because dosing decisions for drugs with a narrow therapeutic window rely on this exposure estimate, the result is inappropriate dosing—either too aggressive or too conservative—based on a misread of how much drug the patient is actually receiving.