Vancomycin Clearance in Obese Adults is not Predictive of Clearance in Obese Adolescents

Background and Objective Contradictory pharmacokinetic (PK) results have been observed between obese adults and obese adolescents, with absolute clearance (CL) reported to be either unaltered, lower, or higher in obese adolescents compared to obese adults. This study investigates the PK of vancomycin in adolescents and adults who are overweight or obese. Methods Data from 125 overweight and obese adolescents (aged 10–18 years, weight 28.3–188 kg) and 81 overweight and obese adults (aged 29–88 years, weight 66.7–143 kg) were analysed using population PK modelling. In addition to age, sex, renal function estimates, and regular weight descriptors, we evaluated standard weight (WT standard , defined as weight for length, age, and sex in adolescents and weight for length in adults) and excess weight (WT excess , defined as total body weight (TBW) minus WT standard ) as covariates in order to distinguish between weight resulting from length versus weight resulting from obesity. Results Analyzing adolescents and adults together, vancomycin CL was found to increase with TBW and decrease with increasing age ( p < 0.001). A covariate analysis investigating adolescents and adults separately found that vancomycin CL increased with WT standard in adolescents and adults, albeit with different functions, with adolescents having a higher CL per WT standard than adults. Moreover, in this separate model, adolescent males had 21% higher CL than adolescent females of the same WT standard , while in adults, CL decreased with increasing age ( p < 0.001). Conclusion There are apparent differences in vancomycin CL in overweight and obese adults versus overweight and obese adolescents, implying that dosing of vancomycin cannot be directly extrapolated between these populations.