# A 60-year-old client is receiving IV gentamicin 1.7 mg/kg every 8 hours for gram-negative sepsis with traditional dosing. The provider orders peak and trough levels around the fourth dose. When does the nurse plan to draw the specimens?

> source: MyMerci (mymerci.kr)  
> url: https://mymerci.kr/pages/nclex_q.php?qn_id=375226&lang=en  
> language: en  
> subject: Medical Emergencies  
> category: PA

## Question

A 60-year-old client is receiving IV gentamicin 1.7 mg/kg every 8 hours for gram-negative sepsis with traditional dosing. The provider orders peak and trough levels around the fourth dose. When does the nurse plan to draw the specimens?

## Option

1. Trough about 30 minutes before the fourth dose, then administer the dose, and draw the peak about 30 minutes after the IV infusion ends; goal traditional peak 5 to 10 mg/L for systemic gram-negative infections and trough less than 2 mg/L; once-daily extended-interval dosing uses a different sampling and nomogram-based protocol. **✔ Correct answer**
2. Draw both peak and trough levels simultaneously at the midpoint between doses, approximately 4 hours after the last dose and 4 hours before the next, to represent the average drug concentration; this method simplifies monitoring and is acceptable for some drugs with predictable kinetics.
3. Draw the peak level 1 hour after starting the IV infusion and the trough 1 hour before the next scheduled dose; these collection times reflect the drug concentration at the end of the infusion and the lowest level before redosing; this timing is commonly used for drugs with a short half-life and a narrow therapeutic index.
4. Peak and trough monitoring is generally not required for gentamicin because its therapeutic window is wide and short courses rarely cause toxicity; levels are typically reserved for patients with renal dysfunction, prolonged therapy, or concomitant use of other nephrotoxic drugs.

**Correct answer: 1**

## Explanation

Aminoglycosides (gentamicin, tobramycin, amikacin, streptomycin) are concentration-dependent bactericidal antibiotics with narrow therapeutic windows requiring drug level monitoring. Two dosing strategies: (1) traditional multiple daily dosing — typical 1 to 2 mg/kg every 8 hours; trough drawn 30 minutes before the next scheduled dose; peak drawn 30 minutes after a 30-minute IV infusion ends (or 60 minutes after IM); steady state at the third or fourth dose; goal peak depends on indication (5 to 10 mg/L for systemic gram-negative; up to 8 to 10 for serious infections), trough less than 2 mg/L to limit toxicity; (2) extended-interval (once-daily, "high-dose pulse") — typical 5 to 7 mg/kg every 24 hours, monitored using a single drug level 6 to 14 hours post-dose plotted on a nomogram (Hartford), or random level 8 to 12 hours after dose to confirm clearance, with goal undetectable trough at 24 hours; this strategy maximizes concentration-dependent killing and post-antibiotic effect while limiting nephrotoxicity and ototoxicity. Both strategies require renal function monitoring (creatinine, urine output) and ototoxicity surveillance (hearing changes, tinnitus, vertigo). Drawing both at midway, both before the dose, or no levels at all are unsafe because of the narrow therapeutic window.

## In-depth explanation

Trough = 30 minutes before next dose, peak = 30 minutes after IV infusion ends. Goal trough

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