Measurement of Skeletal Muscle Area Improves Estimation of Aminoglycoside Clearance across Body Size.

A consistent approach to the dosing of aminoglycosides across the modern body size distribution has been elusive. We evaluated whether radiologically derived measures of body composition could explain more of the interpatient variability in aminoglycoside pharmacokinetics (PK) than standard body size metrics. This retrospective study included adult patients treated with gentamicin or tobramycin with at least three drug concentrations and computed tomography (CT) imaging available. Aminoglycoside volume and clearance (CL) estimates were computed using a two-compartment model by Bayesian analysis. Morphomic data were extracted from CT images using a custom algorithm. Bivariable and multivariable linear regression were used to assess relationships between PK parameters and covariates. A total of 335 patients were included with a median (minimum, maximum) of 4 (3, 16) aminoglycoside concentrations per patient. The median (minimum, maximum) age, height, and weight of included patients were 57 (21, 93) years, 170 (145, 203) centimeters, and 81 (42, 187) kilograms. Both standard and morphomic measures poorly explained variability in volume (R2 < 0.06). Skeletal muscle area and volume explained more of the interpatient variability in CL than weight or sex. Higher precision was observed using a modified Cockcroft-Gault equation with skeletal muscle area at L3 (R2= 0.38) or L4 (R2= 0.37) than the standard Cockcroft-Gault equation using lean (R2= 0.23), adjusted (R2= 0.23), or total (R2= 0.22) body weights. These results highlight that skeletal muscle measurements from CT images obtained in the course of care can improve the precision of aminoglycoside CL estimation over current body size scalars.