The nurse is to administer the patient's next dose of vancomycin at 9:30 a.m. What time will the nurse draw the patient's blood to check the trough vancomycin level?

Choice A reason: Drawing at 8:30 a.m., 60 minutes before, is too early; trough levels, taken just before the next dose, reflect minimum concentration, and this timing risks inaccurate results. Choice B reason: At 9:00 a.m., 30 minutes before the 9:30 a.m. dose, the trough level accurately measures the lowest vancomycin concentration, ensuring therapeutic monitoring aligns with pharmacokinetics. Choice C reason: Drawing at 10:00 a.m., after the dose, measures a post-infusion level, not the trough; this timing misses the minimum concentration critical for dosing adjustments. Choice D reason: At 10:30 a.m., well after the dose, blood reflects peak or random levels, not the trough, skewing data needed to assess vancomycin’s therapeutic efficacy and safety.