Unfolding Case: The Trough That Was Drawn Too Early

The case

0900 day 1 A 68-year-old adult inpatient begins intravenous vancomycin, a glycopeptide antibiotic, every 12 hours for a confirmed deep tissue infection. Piperacillin-tazobactam is running concurrently. Admission serum creatinine 0.9. Urine output 60 mL per hour.

2130 day 2 During the infusion the patient develops flushing and itching across the upper torso and neck. The infusion is slowed and the reaction resolves without other treatment.

0700 day 3 Over the previous shift, urine output has fallen to 20 mL per hour. Serum creatinine is now 1.7.

0700 day 3 A vancomycin trough is collected. The dose is scheduled for 0900. The specimen was drawn at 0700, two hours before the dose, rather than within the window immediately preceding it. The reported level is 24 mcg per mL, above the value the prescriber is targeting → BOOK 07 · P8.

Step 1 · Recognize cues. Which findings require the nurse's attention? Select all that apply.

1. Urine output falling from 60 mL per hour to 20 mL per hour
2. Serum creatinine rising from 0.9 to 1.7
3. A drug level whose documented collection time does not match protocol
4. Flushing and itching during the previous infusion
5. Concurrent piperacillin-tazobactam
6. The patient's age of 68 Answers: 1, 2, 3, 4, 5.

Step 2 · Analyze cues. What is the nurse's best interpretation of the reported level of 24 mcg per mL?

1. The level is valid and confirms accumulation.
2. A trough drawn 2 hours early is not a trough; the number reflects a different point on the elimination curve and cannot be compared to a target.
3. The level is invalid because the patient received a concurrent antibiotic.
4. The level is expected to be high on day 3 of therapy and needs no action. Answer: 2.

Step 3 · Prioritize hypotheses. Which concern takes priority?

1. The elevated number itself
2. Emerging nephrotoxicity, with the invalid specimen preventing any dose decision
3. Recurrence of the infusion reaction
4. Patient discomfort from repeated venipuncture Answer: 2.

Step 4 · Generate solutions. Which actions are within the nurse's scope here? Select all that apply.

1. Hold the 0900 dose pending prescriber clarification
2. Request a redraw within the correct window before the next dose
3. Report the urine output and creatinine trend together
4. Slow the rate of future infusions to prevent recurrence of the reaction
5. Reduce the vancomycin dose by half and document the change
6. Raise the concurrent nephrotoxic therapy with the prescriber Answers: 1, 2, 3, 4, 6.

Step 5 · Take action. Which does the nurse do first?

1. Document the reaction in the electronic record
2. Notify the prescriber, stating the collection time explicitly and reporting the renal trend
3. Redraw the level immediately
4. Restart the infusion at the previous rate Answer: 2.

Step 6 · Evaluate outcomes. Which findings indicate the plan is working? Select all that apply.

1. The repeat level is drawn in the correct window and is reported as valid
2. Urine output rises above the prior shift's total
3. No flushing occurs on the slower infusion rate
4. Serum creatinine continues to climb
5. The patient reports the infusion site is comfortable Answers: 1, 2, 3, 5.

Watch outtwo nephrotoxic agents running together multiply risk rather than add it. The pairing itself is a reportable finding.

Margin notea number with the wrong timestamp is not a number. No trough target is printed → BOOK 07 · P8. No rate is calculated → BOOK 06. The clinical judgment steps themselves → BOOK 02.

TakeawayBefore acting on a drug level, verify when it was drawn.