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Therapeutic drug monitoring (TDM) relies on precise timing to correlate serum concentrations with dosing. A trough represents the lowest concentration before the next dose and is collected immediately prior to administration of that dose. Option B is correct and ensures the result reflects baseline accumulation and clearance, guiding dosing adjustments to avoid toxicity while maintaining efficacy. Option A describes a peak, not a trough; peak timing varies by drug and route (e.g., 30–60 minutes post-infusion for some agents), and collecting at peak when a trough is ordered would invalidate interpretation. Option C is overly rigid and does not account for regimen-specific kinetics. Option D undermines the purpose of TDM, as random timing yields uninterpretable data. The phlebotomist’s role includes confirming the exact dosing time with nursing/pharmacy, documenting collection time accurately, and prioritizing these draws as “timed” alongside STAT needs. Proper coordination prevents recollection, supports patient safety (especially with nephrotoxic antibiotics like aminoglycosides), and meets quality objectives tested on certification exams.