What is the recommended vancomycin dose for a 77-year-old patient with impaired renal function (serum creatinine 40) and a weight of 75 kg, targeting a trough level of 10-13?

Vancomycin Dosing for 77-Year-Old with Renal Impairment

Recommended Dosing Regimen

For this 77-year-old patient weighing 75 kg with a serum creatinine of 40 μmol/L (approximately 0.45 mg/dL, indicating excellent renal function), start vancomycin at 1125 mg (15 mg/kg) every 12 hours, infused over at least 60 minutes, with trough monitoring before the fourth dose. 1, 2

Dosing Calculation and Rationale

• Initial dose: Calculate using 15 mg/kg of actual body weight: 75 kg × 15 mg/kg = 1125 mg per dose 1, 2

• Dosing interval: Every 12 hours is appropriate given the excellent renal function (SCr 40 μmol/L = 0.45 mg/dL suggests CrCl >100 mL/min) 2

• Target trough of 10-13 mg/L: This falls within the acceptable range for non-severe infections (10-15 mg/L), though it's at the lower end of the range for serious infections (15-20 mg/L) 3, 1

• Infusion rate: Each dose must be administered over at least 60 minutes (or at a rate ≤10 mg/min, whichever is longer) to minimize infusion-related reactions 2

Age-Specific Considerations

• Elderly patients may require dose reductions despite apparently normal serum creatinine, as creatinine production decreases with age and muscle mass, potentially overestimating true renal function 2

• The Cockcroft-Gault equation adjusted for age provides a more accurate estimate of renal function in elderly patients: CrCl = [(140 - 77) × 75 kg] / (72 × 0.45) = 146 mL/min 2

• However, this calculated clearance likely overestimates actual renal function in elderly patients due to decreased muscle mass, so conservative dosing is warranted 2

Therapeutic Monitoring Protocol

• Obtain first trough level before the fourth or fifth dose to ensure steady-state conditions 3, 1

• Target trough: 10-13 mg/L as specified, which is appropriate for most infections but may be subtherapeutic for serious MRSA infections (bacteremia, endocarditis, osteomyelitis, pneumonia) where 15-20 mg/L is preferred 3, 1

• Monitor serum creatinine closely for nephrotoxicity, defined as increases ≥0.5 mg/dL or ≥50% from baseline after several days of therapy 3

Dose Adjustment Algorithm

• If initial trough <10 mg/L: Increase dose by 15-20% or decrease dosing interval to every 8 hours 3

• If initial trough 10-13 mg/L: Continue current regimen (target achieved) 1

• If initial trough >13 mg/L but <20 mg/L: Consider maintaining current dose if treating serious infection, or reduce dose if treating non-severe infection 3, 1

• If trough >20 mg/L: Hold next dose, recheck trough, and resume at reduced dose or extended interval once trough decreases to target range 3

Critical Pitfalls to Avoid

• Do not use standard 1 g every 12 hours dosing without weight-based calculation, as this may result in underdosing in this 75 kg patient 1

• Do not target troughs of 15-20 mg/L for non-severe infections as this unnecessarily increases nephrotoxicity risk, especially in elderly patients 3, 1

• Do not rely solely on serum creatinine in elderly patients—the low SCr of 40 μmol/L may reflect decreased muscle mass rather than truly excellent renal function 2, 4

• Avoid concomitant nephrotoxic agents (aminoglycosides, NSAIDs, contrast) as these significantly increase vancomycin-associated nephrotoxicity risk 3

• Do not switch between dosing protocols mid-therapy without rechecking levels, as this increases risk of subtherapeutic or toxic concentrations 5

Alternative Consideration

• If treating a serious MRSA infection (not specified in question), consider a loading dose of 1875-2250 mg (25-30 mg/kg) to rapidly achieve therapeutic concentrations, followed by the maintenance regimen above 1