Frequency of Accurate Vancomycin Monitoring for Adult Patients in an Acute Tertiary Care Hospital: Implications for Patient Care

Background: Vancomycin is used widely for the treatment of infections due to gram-positive organisms including methicillin-resistant Staphylococcus aureus. Because of vancomycin’s complex pharmacokinetic profile and the need to achieve levels well above the isolate’s minimum inhibitory concentration while avoiding nephro- and ototoxicity, monitoring of serum vancomycin concentrations is standard of care. The quality of data resulting from therapeutic drug monitoring (TDM), however, has remained suboptimal. In January 2009 new guidelines for serum vancomycin TDM were released. 

Objective: We investigated to what extent the new guidelines are followed at our institution and whether the information obtained from vancomycin TDM is accurate and leads to appropriate dosage adjustments.
 Methods: We conducted a retrospective audit of vancomycin TDM on 63 randomly selected adult inpatients who received this drug in August 2009. Information was extracted regarding reason for TDM request, initial vancomycin dosage ordered, number of doses administered before first trough, accuracy of timing of drug level measurement, and resulting dosage changes. All parameters were coded as either appropriate or inappropriate according to the current guidelines.
Results: The initial loading dose was appropriate in 41% of the study population. Almost half of the patients (46%) received loading doses lower than recommended. Of all requests sent for TDM, one third were found to be unnecessary, an additional 43% were obtained too early in the course of treatment (i.e., before steady-state conditions were achieved). Inaccurate trough levels that subsequently led to inappropriate dosing adjustments were found in 62% of cases. Overall, the information provided by vancomycin TDM was accurate in only 14%.

Conclusions: The quality of information obtained from vancomycin TDM continues to be poor owing to inaccurate or unnecessary trough measurements as well as incorrect loading doses. Better vancomycin TDM must include use of a weight-based initial loading dose, measurement of drug levels at the correct time (just prior to administration of the next dose), and TDM measurements taken only during steady-state conditions. We are implementing an educational program for our physicians and nurses, as well as a pharmacist-run vancomycin protocol that we believe will increase the appropriate use of vancomycin, save money, and result in better patient care at our institution.