A Prospective Pharmacokinetic Study of Docetaxel in Breast Cancer Patients in Relation to CYP3A4 Activity

Purpose: To study the correlation between pharmacokinetics & pharmacodynamic of docetaxel and CYP3A4 activity in Egyptian cancer patients. Patients and methods: Fourteen Egyptian female Patients with metastatic breast cancer, World Health Organization (WHO) performance status 0 to 2, had received prior chemotherapy regimen, were treated with single-agent docetaxel (100 mg/m2), given every 21 days. Hydrocortisone 300 mg IV was administered 2 days before docetaxel treatment and Cytochrome 3A4 activity was determined by measuring the level of urinary metabolites of 6β-hydroxy cortisol (6β-OHF) and cortisol (FC). For the pharmacokinetic study, Blood samples were taken before and after IV infusion for 1 hr of 100 mg/m2 docetaxel. The level of the drug was determined using HPLC and the correlation between pharmacokinetics and CYP3A4 activity were determined. Results: After cortisol administration, the total amount of 24-hour urinary 6β-OHF and FC were19.97 ± 10.43 and 16.84 ± 10.36 mg/24 h (mean ± SD) respectively. On the other hand, the 6β-OHF/FC ratio after cortisol administration was 1.86 ± 1.933. The pharmacokinetic parameters of docetaxel were clearance 19.9 ± 4.5 L/hr, the volume of distribution 65.6 ± 28.6 L (mean ± SD) and AUC 7.2 μg/ml.hr (range 5-8.8 μg/ml.hr) ± SD). A significant correlation was found between 6β-OHF/FC ratio and neutropenia (p=0.04) in addition correlation between 6β-OHF and Cmax (p=0.04). Conclusion: The interpatient variability of CYP3A4 activity in each patient could be predicted by measuring the total amount of 24 hour urinary 63-OHF after cortisol administration. Individualized dosing to optimize drug exposure for each patient could be performed based on this method. A farther study of fixed versus individualized dosing of docetaxel is needed to determine whether individualized chemotherapy with the application of this method can reduce PK and toxicity variability.