IMPROVING ACHIEVEMENT OF THERAPEUTIC FIRST VANCOMYCIN TROUGH LEVELS IN PATIENTS WITH BONE AND JOINT INFECTION

Introduction & Aim Vancomycin is commonly used in bone and joint infections, but achieving therapeutic targets can be difficult, particularly in patients with preserved renal function. On a specialist bone infection unit, this may lead to frequent subtherapeutic early levels and delayed dose optimisation. This quality improvement project aimed to determine the proportion of patients with a subtherapeutic first vancomycin trough level and identify modifiable factors contributing to this. Methods A retrospective review was undertaken of 252 courses of intravenous vancomycin for bone and joint infection from March 2025 to February 2026. Patients with estimated glomerular filtration rate (eGFR) below 20 mL/min/1.73 m 2 were excluded, as these are managed according to different dosing guidelines. Data were collected from electronic prescribing systems and clinical records, including age, renal function, loading dose, maintenance dose, timing of maintenance dosing, timing of first trough measurement, prescription location, dose adjustment, and acute kidney injury. The primary outcome was the percentage of subtherapeutic first trough levels, defined as less than 15 mg/L. Results Mean patient age was 59.7 years. 132/252 (52.4%) patients had an eGFR above 90. Process errors were common: 80/248 (32.3%) first trough levels were taken at an incorrect time point, of which 40/80 (50%) were due to sampling before the third maintenance dose rather than before the fourth in twice-daily regimens. Where maintenance dosing was due 12 hours after the loading dose 127/238 (53.4%) doses were started late, with mean delay of 4.1 hours. Documentation of loading doses was often difficult to interpret, particularly when prescribing was split between documents. Prescription location varied, with approximately 83/252 (33.1%) on standard electronic prescribing, 69/252 (27.6%) on anaesthetic electronic prescribing, and 88/252 (34.6%) on the anaesthetic record. Among patients with trough levels measured correctly, 95/168 (56.5%) were subtherapeutic. The proportion sub-therapeutic increased to 70/90 (71.4%) among patients with eGFR above 90. Among patients with correctly timed trough levels and with correct loading and maintenance doses, 80/142 (56.3%) were below the therapeutic target. In total 53/80 (66.3%) had serum vancomycin levels 10-14.9mg/L, and 27/80 (33.8%) had levels <10mg/L. Conclusions Subtherapeutic first vancomycin trough levels are common in bone and joint infection, particularly in patients with preserved renal function. Contributing factors include delayed or inappropriate maintenance dosing, incorrect trough timing, and poor visibility of loading-dose documentation across prescribing platforms, which are clear targets for future quality improvement interventions. However, subtherapeutic levels are also common despite appropriate prescriptions.