Association of older age and lower body mass index with initial teicoplanin trough concentrations: a single-center retrospective cohort study

Abstract Background The pharmacokinetics of teicoplanin and optimal loading strategies remain poorly characterized in older underweight patients. This retrospective, single-center, observational study evaluated the initial trough concentration (C min ) of teicoplanin in this population. Methods Among 199 enrolled patients, C min was compared between the older underweight group (aged ≥ 75 years and body-mass-index [BMI] < 18.5 kg/m 2 ) and the control group. Multivariable linear regression analyses were performed to confirm the associations of age and BMI with C min , adjusting for estimated glomerular filtration rate, serum albumin, serum alanine aminotransferase, admission to the intensive care unit, and the loading dose of teicoplanin. As exploratory analyses, C min values and the dose–C min relationship were evaluated in 4 subgroups classified by age (≥ 75 or < 75 years) and BMI (< 18.5 or ≥ 18.5 kg/m²). The early clinical response was assessed in 28 patients with bacteremia requiring teicoplanin treatment. Results The median C min was 17.1 µg/mL (interquartile range [IQR]: 14.3–18.5 µg/mL) in the older underweight group, and 18.8 µg/mL (IQR: 15.8–22.7 µg/mL) in the control group ( P < 0.01). Multivariable linear regression analyses revealed that teicoplanin concentration decreased by 0.80 µg/mL per 10-year increase in age and by 0.30 µg/mL per 1.0 kg/m² decrease in BMI. The dose of teicoplanin exhibited the strongest effect on C min among the tested explanatory variables, with C min increasing by 1.17 µg/mL per 1.0 mg/kg. Among the 4 subgroups, the older underweight group showed the smallest regression coefficient (C min increasing by 0.66 µg/mL per 1.0 mg/kg dose increment). The median (IQR) teicoplanin C min was 20.0 (18.4–22.5) µg/mL in patients with a clinical response ( n = 18) and 17.8 (15.4–18.9) µg/mL in those without a clinical response ( n = 10). The difference was not statistically significant (Hodges–Lehmann estimated median difference, 2.40 µg/mL; 95% CI, − 0.70 to 5.50). Conclusions The older underweight group exhibited lower C min values than controls. The C min decreased with increasing age and decreasing BMI. Our findings highlight the need for further prospective studies to evaluate the efficacy and safety of individualized loading strategies in the older underweight population.