Impact of Curcumin (with or without Piperine) on the Pharmacokinetics of Tamoxifen.

Tamoxifen is a prodrug that is primarily metabolized into the pharmacologically active metabolite endoxifen and eventually into inactive metabolites. The herb curcumin may increase endoxifen exposure by affecting phase II metabolism. We compared endoxifen and tamoxifen exposure in breast cancer patients with or without curcumin, and with addition of the bio-enhancer piperine. Tamoxifen (20⁻30mg per day (q.d.)) was either given alone, or combined with curcumin (1200 mg three times daily (t.i.d.)) +/- piperine (10 mg t.i.d.). The primary endpoint of this study was the difference in geometric means for the area under the curve (AUC) of endoxifen. Genotyping was performed to determine CYP2D6 and CYP3A4 phenotypes. The endoxifen AUC0⁻24h decreased with 7.7% (95%CI: -15.4 to 0.7%; p = 0.07) with curcumin and 12.4% (95%CI: -21.9 to -1.9%; p = 0.02) with curcumin and piperine, compared to tamoxifen alone. Tamoxifen AUC0⁻24h showed similar results. For patients with an extensive CYP2D6 metabolism phenotype (EM), effects were more pronounced than for intermediate CYP2D6 metabolizers (IMs). In conclusion, the exposure to tamoxifen and endoxifen was significantly decreased by concomitant use of curcumin (+/- piperine). Therefore, co-treatment with curcumin could lower endoxifen concentrations below the threshold for efficacy (potentially 20⁻40% of the patients), especially in EM patients.

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.