Vancomycin Dosing in Renal Impairment
A 75-year-old woman (weight 60 kg, height 160 cm) is admitted with MRSA bacteremia. Her serum creatinine is 2.0 mg/dL (stable). She is prescribed vancomycin 1 g IV every 12 hours. After 3 days, a trough level drawn just before the 4th dose is 28 mg/L (target 10–15 mg/L for bacteremia, but some guidelines recommend 15–20 mg/L for serious infections). The patient's renal function is estimated by Cockcroft-Gault: CrCl = [(140-75) × 60] / (72 × 2.0) × 0.85 = 23 mL/min.
1. Calculate the patient's creatinine clearance and evaluate the appropriateness of the current vancomycin dose.
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CrCl = [(140 - age) × weight (kg)] / (72 × SCr) × 0.85 (for female) = [(140-75) × 60] / (72 × 2.0) × 0.85 = (65 × 60) / 144 × 0.85 = 3900 / 144 × 0.85 = 27.08 × 0.85 ≈ 23 mL/min.
The patient has severe renal impairment (CrCl <30 mL/min). The standard vancomycin dose of 1 g every 12 hours is too high. For CrCl 20–30 mL/min, typical dosing is 15–20 mg/kg loading dose then 250–500 mg every 24 hours or based on levels. The trough of 28 mg/L is supratherapeutic and increases risk of nephrotoxicity and ototoxicity.
2. Recommend a new dosing regimen and monitoring plan.
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Recommendation:
- Hold next dose and consider rechecking trough after 24 hours.
- For CrCl 23 mL/min, a loading dose of 25–30 mg/kg (actual body weight) may be given initially, but since patient already has high trough, no loading needed now.
- Maintenance dose: 500 mg IV every 24 hours or 750 mg every 48 hours, with subsequent trough monitoring before the 4th dose of new regimen.
- Target trough for MRSA bacteremia: 15–20 mg/L (per guidelines).
- Monitor renal function daily (SCr, BUN) and urine output.
- Consider infectious disease consult and alternative therapy if nephrotoxicity develops.
- Ensure adequate hydration and avoid other nephrotoxins.