Predictability of vancomycin trough concentrations using seven approaches for estimating pharmacokinetic parameters

Purpose. Seven methods for estimating vancomycin pharmacokinetic parameters were studied to determine which method best predicted measured concentrations for patients at a community teaching hospital. Methods. Data from adult patients who were given vancomycin and had at least one steady-state trough concentration measured were retrospectively reviewed. Data analyzed included laboratory test values, concomitant medications, weight, height, sex, age, laboratory cultures, medical procedures performed, vancomycin dose and interval, measured vancomycin concentrations, and time of measurement. Relevant data were used in seven predictor methods that estimate volume of distribution, vancomycin clearance, and elimination rate constant to determine which yielded the best predictions of actual measured concentrations in the patient population. Results. Data from 189 patients were included in the analyses. The coefficients of determination for the methods ranged from 0.114 to 0.234. Bias ranged from -5.90 to 0.69 mg/L, and precision ranged from 6.05 to 8.08. The Matzke method had the best combination of the least bias and best precision. Predictions were within 2.5 and 5 mg/L of measured concentrations 18.0-43.9% and 43.4-66.1% of the time, respectively. The percentage of predictions within 25% and 50% of measured concentrations ranged from 7.9% to 31.2% and from 18.0% to 48.1%, respectively. Ten (5.3%) patients had trough concentrations exceeding 20 mg/L, and 11 (5.8%) had trough concentrations of <= 3 mg/L. Conclusion. The seven methods studied for estimating vancomycin pharmacokinetic parameters varied widely in predicting vancomycin trough concentrations compared with measured serum concentrations and were not sufficiently reliable to replace therapeutic monitoring of vancomycin serum concentrations.