Limited inter-occasion variability in relation to inter-individual variability in chemotherapy-induced myelosuppression

Purpose: A previously developed semi-physiological model of chemotherapy-induced myelosuppression has shown consistent system-related parameter and inter-individual variability (IIV) estimates across drugs. A requirement for dose individualization to be useful is relatively low variability between treatment courses (IOV) in relation to IIV. The objective of this study was to evaluate and compare magnitudes of IOV and IIV in myelosuppression model parameters across six different anti-cancer drug treatments.Methods: Neutrophil counts from several treatment courses following therapy with docetaxel, paclitaxel, epirubicin-docetaxel, 5-fluorouracil-epirubicin-cyclophosphamide, topotecan and etoposide were included in the analysis. The myelosuppression model was fitted to the data using NONMEM VI. IOV in the model parameters baseline neutrophil counts (ANC0), mean transit time through the non-mitotic maturation chain (MTT) and the parameter describing the concentration-effect relationship (Slope) were evaluated for statistical significance (P < 0.001).Results: IOV in MTT was significant for all the investigated datasets, except for topotecan, and was of similar magnitude (8-16 CV %). IOV in Slope was significant for docetaxel, topotecan and etoposide (19-39 CV %). For all six investigated datasets the IOV in myelosuppression parameters was lower than the IIV. There was no indication of systematic shifts in the system- or drug sensitivity-related parameters over time across data sets.Conclusion: This study indicates that the semi-physiological model of chemotherapy-induced myelosuppression has potential to be used for prediction of the time-course of myelosuppression in future courses and is thereby a valuable step towards individually tailored anticancer drug therapy