Muscle mass affects paclitaxel systemic exposure and may inform personalized paclitaxel dosing

Aims: Patients with low muscle mass have increased risk of paclitaxel-induced peripheral neuropathy, which is dependent on systemic paclitaxel exposure. Dose optimization may be feasible through the secondary use of radiologic data for body composition. The objective of this study was to interrogate morphomic parameters as predictors of paclitaxel pharmacokinetics to identify alternative dosing strategies that may improve treatment outcomes. Methods: This was a secondary analysis of female patients with breast cancer scheduled to receive 80 mg/m(2) weekly paclitaxel infusions. Paclitaxel was measured at the end of initial infusion to estimate maximum concentration (C-max). Computed tomography (CT) scans were used to measure 29 body composition features for inclusion in pharmacokinetic modelling. Monte Carlo simulations were performed to identify infusion durations that limit the probability of exceeding C-max > 2885 ng/mL, which was selected based on prior work linking this to an unacceptable risk of peripheral neuropathy. Results: Thirty-nine patients were included in the analysis. The optimal model was a two-compartment pharmacokinetic model with T11 skeletal muscle area as a covariate of paclitaxel volume of distribution (Vd). Simulations suggest that extending infusion of the standard paclitaxel dose from 1 hour to 2 and 3 hours in patients who have skeletal muscle area 4907-7080 mm(2) and <4907 mm(2), respectively, would limit risk of C-max > 2885 ng/mL to <50%, consequently reducing neuropathy, while marginally increasing overall systemic paclitaxel exposure. Conclusion: Extending paclitaxel infusion duration in similar to 25% of patients who have low skeletal muscle area is predicted to reduce peripheral neuropathy while maintaining systemic exposure, suggesting that personalizing paclitaxel dosing based on body composition may improve treatment outcomes.