Vancomycin is a primary therapy for methicillin-resistant Staphylococcus aureus infections, but its pharmacokinetics show considerable variability, particularly among older adults. Data on factors affecting vancomycin pharmacokinetics in Saudi adult patients are scarce. This study aimed to develop a population pharmacokinetic (Pop-PK) model for vancomycin in medical ward patients and to identify patient-specific factors influencing trough concentrations.We conducted a retrospective multicenter study including patients aged 40 years or older admitted to medical wards in the Eastern Province of Saudi Arabia and treated with vancomycin from January to December 2022. Non-linear mixed-effects modeling (Monolix) was used to construct the Pop-PK model, with the base model chosen based on the Akaike information criterion. Covariates analyzed were age, sex, body weight, C-reactive protein (CRP), serum creatinine, creatinine clearance (CrCl), and albumin. Covariates were retained in the final model if P < 0.05 using stepwise addition. Model adequacy was evaluated with visual predictive checks, and simulations using Simulx assessed the impact of the significant covariates on vancomycin trough levels.Data from 124 patients encompassing 172 vancomycin trough measurements were included. The final Pop-PK model followed a one-compartment structure with linear elimination. CrCl and CRP were identified as the significant covariates, reducing between-subject variability in clearance from 173% to 81%. Simulations suggested that higher CRP and lower CrCl were associated with elevated vancomycin trough concentrations.Considerable variability exists in vancomycin trough levels among patients, and this study highlights the influence of renal function and systemic inflammation, reflected by CrCl and CRP, on vancomycin pharmacokinetics in non-critical medical ward patients.
