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/m2) and who gave written informed consent were randomized to receive either the 1st 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 (AUC0‐inf) 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 (AUC0‐inf 2784 ng*h/mL, 95% confidence interval 2436–3183 ng*h/mL) was similar to the concentration of docetaxel monotherapy (AUC0‐inf 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.