Background and Importance Information regarding the impact of obesity on the pharmacokinetics of most drugs is limited. Obesity is associated with physiopathological changes that may affect the pharmacokinetics of vancomycin. Therefore, there is a need for pharmacokinetic models specific to the obese population to optimise dosing schedules in this group of patients.

Aim and Objectives To determine the differences in pharmacokinetic parameters (PKP) in hospitalised obese patients.

Material and Methods Retrospective observational study including adult patients who had a plasmatic concentration of vancomycin between March 2022 and August 2023. Critically ill patients and those with renal failure were excluded. Demographic variables collected were: sex, age, weight, height, body mass index (BMI), PKP (volume of distribution (Vc), stade state volume of distribution (Vss), clearance (Cl), half-life (t_1/2)), peak (Cmax) and through (Cmin) level, start date of vancomycin treatment and sample collection date. Patients were grouped according to BMI: obese (BMI ≥30 kg/m²) and non-obese (BMI <30 kg/m²). All data were collected from electronic health records and pharmacokinetic reports. This report includes the PKP calculated using a pharmacokinetic programme (PKS®), based on a bicompartimental model. Data were analyced by SPSS statistics 21®. Qualitative variables were presented by frecuency and quantitative variables by mean ± standard deviation and median (interquartile range). T-student and U-Mann-Whitney were used to compare parametric and non-parametric variables.

Results 57 patients (63.2% men) with a mean age of 67.3±12.8 years. 17.5% were obese. The pharmacokinetic data in the obese group were: Cmin=10±7.7 mg/L, Cmax=39.3± 28.1 mg/L, Vc=19.8 (19–23.4) L, Vss=74.6±19.8 L, Cl=5 ±2.4 L/h, t_1/2=11.4 (7.5–15.2) h. The pharmacokinetic data in the non-obese group were: Cmin=12 (9–16.7) mg/L, Cmax=24.7±7.2 mg/L, Vc=14.4±2.3 L, Vss=49.1±8.8 L, Clp=4 (3.25–4.59) L/h, t_1/2=9.6 (8.1–12.1) h. Statistically significant differences were only found between both groups in Vc (p<0.05) and Vss (p<0.05).

Conclusion and Relevance The volume of distribution (Vc and Vss) in obese patients is higher than in non-obese patients, with significant differences being found. For the rest of pharmacokinetic data, no significant differences were found. It is necessary to carry out studies that allow designing a pharmacokinetic model of vancomycin in obese patients in order to optimise treatment.

Conflict of Interest No conflict of interest.