Population pharmacokinetic and exposure-toxicity analyses of nab-paclitaxel after pegylated recombinant human granulocyte colony-stimulating factor administration in patients with metastatic breast cancer.

PURPOSE

This study aimed to establish a population pharmacokinetic (PK) model to evaluate the dynamic relationship between the concentrations of total and unbound paclitaxel, and the exposure-response analysis of albumin-bound paclitaxel (nab-paclitaxel) after pegylated recombinant human granulocyte colony-stimulating factor (PEG-G-CSF) administration in patients with metastatic breast cancer.

METHODS

A total of 653 concentrations corresponding to total paclitaxel and 334 concentrations corresponding to unbound paclitaxel were analyzed in 24 subjects who randomized received a single 260 mg/m dose of two nab-paclitaxel formulations with a 21-35-day washout period. PEG-G-CSF was administered to all the patients in each cycle to prevent neutropenia. The exposure-response relationships were evaluated using the exposure to total, albumin-coated, and unbound paclitaxel, as well as the reduction in neutrophil count. The exposure data were analyzed using nonlinear mixed-effect modeling. A linear regression model was used to test the statistical significance of the correlation between percentage of reduction in neutrophil count and exposure.

RESULTS

The PK characteristics of total paclitaxel were described using a three-compartment model with first-order elimination, and a mechanism-based model incorporating linear release of nab-paclitaxel and the saturated binding of unbound paclitaxel to plasma components was established. The release ratio of paclitaxel from nab-paclitaxel was estimated to be 4.60% and the maximum unbound fraction (2.76%) was reached at the end of the infusion. The study found that a longer duration of total paclitaxel concentration > 0.19 µmol/L was significantly correlated with a reduction in neutrophil count (r = 0.23, P = 0.00062). Specifically, a duration of > 8.6 h was a predictor of a decreased neutrophil count.

CONCLUSION

The decrease in neutrophils induced by nab-paclitaxel was significantly correlated with the duration above a total paclitaxel concentration of 0.19 µmol/L despite the use of PEG-G-CSF.