A patient is receiving vancomycin therapy. When should the nurse schedule the collection of blood samples to measure the peak and trough levels of vancomycin?

Vancomycin is a glycopeptide antibiotic used against serious gram-positive infections, including methicillin-resistant Staphylococcus aureus (MRSA). Because of its narrow therapeutic index and risk of nephrotoxicity and ototoxicity, serum drug level monitoring is essential. The peak level represents the highest drug concentration in the blood and is drawn 30 to 60 minutes after the end of the intravenous infusion, when distribution from the vascular compartment into tissues is complete. The trough level represents the lowest concentration, occurring just before the next scheduled dose, and is the sample most widely used to guide dosing adjustments and assess the risk of toxicity. Collecting the peak level immediately before the next dose would actually reflect the trough, not the peak, making that timing incorrect. Collecting both levels one hour before the next dose would only give a trough value and would miss the true peak. Collecting both samples two hours after the infusion ends would not capture the true trough and would give a post-distribution value at best, which does not accurately reflect either pharmacokinetic parameter. The correct protocol — peak at 30 minutes post-infusion and trough just before the next dose — gives clinically meaningful data to optimize vancomycin efficacy while minimizing the risk of toxicity.