Determining the Clinical Relevance of the Interaction Between Enzalutamide and the Opioid Morphine and the DOAC Edoxaban to Improve Rational Pharmacological Care of Patients With Prostate Cancer

Enzalutamide is one of the oncolytic drugs that showed efficacy and safety in most of the features of prostate cancer. Approximately 17% of the patients treated with enzalutamide need pain control. Nearly all opioids are metabolized through one of the CYP enzymes induced by enzalutamide, making optimal pain management difficult. For pain control, while using enzalutamide, morphine is being advised since morphine is mainly glucuronidated by UGT2B7 and to a lesser extent UGT1A1. Enzalutamide is in vitro an inducer of UGT1A1 and may inhibit UGT2B7 which could alter morphine concentrations, though the clinical relevance of this interaction is unknown.

In patients with cancer, Direct Oral Anticoagulants (DOACs) are frequently used since vitamin-K antagonists were reported less effective than DOACs in preventing thromboembolic events. However, DOACs are all metabolized through CYP3A4 or P-gp. Due to interaction potential with DOACs, patients treated with enzalutamide are switched to Low Molecular Weight Heparin (LMWHs) administered subcutaneously which is considered safe but less patient friendly. For patients comfort DOACs are preferred over the use of LMWHs. Since rivaroxaban and apixaban are both major substrates for CYP3A4, combination with enzalutamide is prohibited. Dabigatran is a DOAC which is only metabolized by P-gp and edoxaban is a minor substrate for CYP3A4. Therefore, both might be safe to combine with enzalutamide. However, in patients with an active malignancy edoxaban is preferred according to national guidelines. Still, it is unknown if enzalutamide has a significant effect on the edoxaban exposure.

The purpose of this study is to evaluate the effect of enzalutamide on morphine and edoxaban pharmacokinetics.