# A 55-year-old client is receiving IV vancomycin for MRSA bacteremia. The pharmacist orders a trough level. When does the nurse plan to draw the trough specimen?

> source: MyMerci (mymerci.kr)  
> url: https://mymerci.kr/pages/nclex_q.php?qn_id=375221&lang=en  
> language: en  
> subject: Medical Emergencies  
> category: PA

## Question

A 55-year-old client is receiving IV vancomycin for MRSA bacteremia. The pharmacist orders a trough level. When does the nurse plan to draw the trough specimen?

## Option

1. Any time during the infusion of the second dose.
2. 60 minutes after the third dose finishes infusing.
3. About 30 minutes before the next scheduled dose (typically before the fourth dose) to allow steady state and reflect the lowest serum concentration; goal trough is 15 to 20 mg/L for serious MRSA infections, with AUC-guided dosing increasingly preferred per current guidelines. **✔ Correct answer**
4. At the start of the very first dose to establish a peak.

**Correct answer: 3**

## Explanation

Vancomycin is a glycopeptide antibiotic for serious gram-positive infections including MRSA bacteremia, endocarditis, pneumonia, skin and soft tissue, and bone and joint infections. Therapeutic drug monitoring is essential because of a narrow therapeutic window between efficacy and toxicity. Trough timing: draw the specimen approximately 30 minutes before the next scheduled dose, after steady state is reached (typically before the fourth dose for q12 hour dosing). Goal trough varies by indication: 15 to 20 mg/L for serious MRSA infections (bacteremia, endocarditis, meningitis, osteomyelitis, severe pneumonia) and 10 to 15 mg/L for less invasive infections. Newer 2020 ASHP/IDSA/PIDS/SIDP guidelines recommend area-under-the-curve (AUC) over MIC-targeted dosing (target AUC/MIC 400 to 600) using two levels (peak and trough) or Bayesian software, because trough-only dosing may overshoot and cause AKI. Nursing duties: ensure timing accuracy, label the lab requisition with the dose number and timing, and report the result to the prescriber for adjustment. Drawing 60 minutes after the third dose is for peak-style monitoring (rarely used), drawing at the first dose precedes steady state, and any-time draw during the second-dose infusion is uninterpretable.

## In-depth explanation

Trough = 30 minutes before the next dose at steady state. Goal 15-20 mg/L for serious MRSA. AUC-guided dosing is the new gold standard.

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