Individualized dosing of vancomycin in geriatric patients

Area of Science:

• Pharmacology
• Geriatric Medicine
• Clinical Pharmacy

Background:

• Geriatric pharmacotherapy is complex due to multimorbidity and altered drug metabolism.
• Therapeutic drug monitoring (TDM) individualizes dosing to optimize vancomycin efficacy and minimize toxicity.
• Current vancomycin TDM guidelines (Rybak et al., 2009) focus on trough concentrations.

Purpose of the Study:

• Evaluate vancomycin TDM practices in geriatric and non-geriatric patients.
• Compare trough-based versus AUC-based vancomycin dosing adjustments.
• Identify covariates for optimal initial vancomycin dosing in the elderly.

Main Methods:

• Retrospective analysis of 1,458 vancomycin concentrations from 380 patients.
• Exclusion of hemodialysis patients.
• Pharmacokinetic modeling to assess individual AUC24 values and compare with trough concentrations.

Main Results:

• Initial dosing achieved optimal vancomycin exposure in only 37.8% of patients.
• Trough-based guidelines agreed with AUC-based adjustments in 65% of cases, but missed toxicity/sub-therapeutic levels in others.
• Geriatric patients often required lower vancomycin doses (≤1.5 g/day) compared to non-geriatric patients (3-4 g/day).
• Estimated glomerular filtration rate (eGFR) was a key covariate for dosing.

Conclusions:

• AUC-based vancomycin monitoring is superior to trough-based monitoring.
• Trough-based monitoring can lead to over-dosing in over 25% of patients.
• An eGFR-based nomogram can improve initial vancomycin dose optimization.