Aims Anecdotal evidence has suggested that patients prescribed intermittent intravenous vancomycin infusion do not achieve plasma vancomycin concentrations within the therapeutic range in a timely manner when dosed according to Trust guidelines. The aims of this study were: to evaluate adherence to Trust dosing and therapeutic drug monitoring guidelines¹ for intermittent intravenous vancomycin infusion, and, to determine whether adherence to these guidelines achieves and maintains therapeutic vancomycin plasma concentrations in paediatric patients.

Method A retrospective audit of vancomycin dosing and therapeutic drug monitoring was carried out over a 12-month period. Patients aged between 1 month and 18 years at the start of treatment who were prescribed an inpatient course of intermittent intravenous vancomycin consisting of at least three doses were identified from electronic prescribing records. Electronic medical notes and prescribing records were used to retrieve demographic data, vancomycin prescription data, serum creatinine levels and data relating to vancomycin therapeutic drug monitoring. Vancomycin plasma concentrations between 10–15 mg/L were considered therapeutic unless an alternative range was stated in the patient’s medical notes. Data analysis was conducted on SigmaPlot, Version 14.5. Ethical approval was not required.

Results Fifty treatment courses and an associated 171 plasma vancomycin concentrations were identified and included for analysis. Treatment duration ranged from 2.9 to 50 days (mean 8.9 days). The initial prescribed dose and dosing interval were fully adherent to the guidelines for 41/50 (82%) treatment courses. The initial vancomycin plasma concentration was measured at the recommended time for 20/50 (40%) courses. The action taken in response to a plasma concentration was in accordance with the guideline recommendation in 129/171 (75%) cases. One treatment course was completed without measurement of a vancomycin plasma concentration. Plasma concentrations within the therapeutic range were achieved for 22/49 (45%) treatment courses for which concentrations were monitored. The mean time taken to reach the therapeutic range was 2.3 days (standard deviation 1.9 days) from when treatment was commenced. Collectively, 21.5% of time from all treatment courses was spent with plasma concentrations within the therapeutic range.

Conclusion The study showed good adherence to guidelines for the prescribing of the initial vancomycin dose and dosing frequency. Despite suboptimal timing of the measurement of initial vancomycin plasma concentrations, the actions taken (such as dose alteration) in response to plasma concentrations were in accordance with the guideline in three-quarters of cases. However, less than half of all treatment courses achieved therapeutic plasma concentrations, and for those that did, a mean of 2.3 days from when treatment was commenced was required to reach therapeutic range. This suggests that Trust vancomycin dosing recommendations may be insufficient to achieve plasma concentrations within the therapeutic range in a timely manner for most patients. An increase to the recommended initial dosing of intermittent intravenous vancomycin infusion should be considered.

Reference

1. Paediatric Formulary Vancomycin Monograph, Evelina London Children’s Hospital, Guy’s and St Thomas’ NHS Foundation Trust (2022).