Studying the influence of prednisone on docetaxel exposure.

1.Histologicallly or cytologically confirmed adenocarcinoma of the prostate without neuro-endocrine differentitation or small cell features.

2. Continued androgen deprivation therapy either by gonadotropin releasing hormone (GnRH) analogues or orchiedectomy

3. Age ≥18 years

4. Metastatic disease progression

5. ECOG performance status 0-1

6. Written informed consent according to ICH-GCP

1. Impossibility or unwillingness to take oral drugs

2. Serious concurrent illness or medical unstable condition requiring treatment

3. Symptomatic CNS metastases or history of psychiatric disorder that would prohibit the understanding and giving of informed consent

4. Known hypersensitivity to studiemedication

5. Use of medication or dietary supplements known to induce CYP3A

6. Any active systemic or local bacterial, viral, fungal - or yeast infection.

7. Abnormal renal function defined as (within 21 days before randomization): Serum creatinin > 1.5 x upper limit of normal (ULN). If creatinine 1.0 - 1.5 x ULN, creatinine clearance will be calculated according to CKD-EPI formula and patients with creatinine clearance <60 mL/min will be excluded.

8. Abnormal liver functions consisting of any of the following (within 21 days before randomization):

o Total bilirubin ≥ 1 x ULN (except for patients with documented Gilbert’s disease)

o alanine aminotransferase (ALAT) and aspartate aminotransferase (ASAT) ≥ 2.5 x ULN. (in case of liver metastases >5 x ULN)

o Alkaline phosphatase (AF) > 5 x ULN (in case of bone metastases > 10 x ULN)

9. Abnormal hematological blood counts consisting of any of the following (within 21 days before randomization):

o Absolute neutrophil count ≤ 1.5 x 109/L

o Platelets ≤ 100 x 109/L

10. Geographical, psychological or other non-medical conditions interfering with follow-up