Does one dose fit all? Determinants of therapeutic vancomycin concentrations in adult patients

Background: Recent guidelines suggest aiming for higher trough concentration of Vancomycin. However, the dosing recommendations in place are often insufficient to acheive desired trough concentrations thus leading to significant underdosing of patients.

Objectives: To measure the cumulative dose and time require to reach therapeutic vancomycin concentration and to determine factors affecting therapeutic vancomycin concentration in hospitalized adults.

Settings: A tertiary care teaching hospital of urban Melbourne, Australia.

Method: Patients receiving vancomycin between 15th of April to 15th of May, 2010 were followed until they reached trough vancomycin concentration of more than or equal to 10 mg/L. Following variables were collected: age, gender, weight, eGFR, initial dose (mg/kg), level aims, vancomycin levels and their times and treating unit. Independent sample t test was used to study the differences and Pearson correlations were used to study the relationship between the study variables. Linear regression model was used to determine the predictors of therapeutic vancomycin levels.

Main outcomes measures: Time to reach target trough therapeutic vancomycin concentrations. Results: A total of 46 patients received vancomycin during the study period. Fifteen out of 46 patients were excluded; 5 patients had vancomycin prior to admission, 4 patients received less than 2 doses and levels were not measured in 6 patients. Eleven out of 31 eligible patients were female; no significant differences were observed in study variables based on the gender. The average time required to reach therapeutic vancomycin concentration was 61.8 h. Four patients were unable to reached therapeutic levels while only 6 patients were able to reach therapeutic levels within 24 h. Patients’ age and eGFR were found to be the best predictors of therapeutic vancomycin concentration (Adjusted R2 = 0.929) after eliminating all the other study variables in a stepwise backward linear regression model. No significant correlations were observed between body weight and either cumulative dose required or time to reach therapeutic vancomycin concentrations.

Conclusion: The present study highlights the need of quality initiatives to improve vancomycin prescribing to achieve therapeutic vancomycin concentration earlier in the course of treatment.