Effects of Prednisone on Docetaxel Pharmacokinetics in Men with Metastatic Prostate Cancer: A Randomized Drug-drug Interaction Study

Aims: Docetaxel has been approved for the treatment of metastatic prostate cancer in combination with prednisone. Since prednisone is known to induce the cytochrome P450 iso-enzyme CYP3A4, which is the main metabolizing enzyme of docetaxel in the liver, a potential drug-drug interaction may occur. In this prospective randomized pharmacokinetic cross-over study we investigated docetaxel exposure with concomitant prednisone, compared to docetaxel monotherapy in men with metastatic prostate cancer.

Methods: Patients scheduled to receive at least 6 cycles of docetaxel (75 mg/m ) and who gave written informed consent were randomized to receive either the 1 3 cycles, or the last 3 consecutive cycles with prednisone (twice daily 5 mg). Pharmacokinetic blood sampling was performed during cycle 3 and cycle 6. Primary endpoint was difference in docetaxel exposure, calculated as area under the curve (AUC ) and analysed by means of a linear mixed model. Given the cross-over design the study was powered on 18 patients to answer the primary, pharmacokinetic, endpoint.

Results: Eighteen evaluable patients were included in the trial. Docetaxel concentration with concomitant prednisone (AUC 2784 ng*h/mL, 95% confidence interval 2436-3183 ng*h/mL) was similar to the concentration of docetaxel monotherapy (AUC 2647 ng*h/mL, 95% confidence interval 2377-2949 ng*h/mL). Exploratory analysis showed no toxicity differences between docetaxel monotherapy and docetaxel cycles with prednisone.

Conclusion: No significant difference in docetaxel concentrations was observed. In addition, we found similar toxicity profiles in absence and presence of prednisone. Therefore, from a pharmacokinetic point of view, docetaxel may be administrated with or without prednisone.