The benefits of antimicrobial prophylaxis for cardiac surgery have been clearly demonstrated in placebo-controlled studies. Prophylactic intravenous antibiotics are therefore administered, with agent selection directed against the most common skin-colonising and gram-negative bacteria. Controversy persists regarding the optimal antimicrobial choice and duration of administration for cardiac surgery. In settings with a high incidence of methicillin-resistant Staphylococcus aureus (MRSA), administration of cefazolin or vancomycin for prophylaxis is considered reasonable (Class IIB recommendation, Level of Evidence C).

Vancomycin, a glycopeptide antibiotic, is widely used to treat serious gram-positive infections, including those caused by MRSA and methicillin-resistant Staphylococcus epidermidis (MRSE). Extensive pharmacokinetic/pharmacodynamic (PK/PD) studies reveal marked variability in population PK parameters across patient groups; clearance variability may reach 45 % and volume of distribution variability 48 %.

Oral vancomycin absorption is poor (≈5 % bioavailability), yet luminal concentrations remain sufficiently high for efficacy against Clostridioides difficile-associated pseudomembranous colitis. Inter-individual PK variability is substantial; two- or three-compartment models are typically employed. Protein binding ranges from 30 % to 50 %. Approximately 90 % of the dose is eliminated unchanged via the kidneys; biliary elimination is minimal. The elimination half-life is 4-7 h in individuals with normal renal function and is prolonged in patients >65 years or with renal impairment. Obesity, age, renal function, concomitant medications, disease state, and peri-operative interventions can all influence vancomycin clearance and apparent volume of distribution, potentially yielding sub- or supra-therapeutic serum concentrations.

To characterise current therapeutic drug monitoring (TDM) practices for vancomycin in cardiac-surgery patients undergoing cardiopulmonary bypass, this retrospective study combined multimodal data to develop a prognostic model predicting high- or low-risk vancomycin serum levels post-operatively. Model performance was evaluated to provide an evidence base for individualised dosing strategies aimed at optimising efficacy and minimising adverse effects.

Pharmacokinetic datasets from post-cardiac-surgery patients receiving cardiopulmonary bypass were analysed to identify determinants of vancomycin blood concentrations. Integration of baseline characteristics and medication records supports early intervention guidance for individualised vancomycin dosing and optimisation of anti-infective therapy.

Inclusion Criteria:

• Undergoing cardiac surgery with cardiopulmonary bypass
• Received intravenous vancomycin postoperatively for infection prophylaxis or treatment

Exclusion Criteria:

• Age <18 years
• Missing data on weight, height, or serum creatinine during vancomycin therapy
• No vancomycin trough plasma concentration recorded

Patients requiring cardiac surgery for conditions such as valvular heart disease who received postoperative vancomycin for infections.