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[A Survey on the Concomitant Use of Drugs with Enzalutamide in Medical Practice-The Effects and Resultant Decrease in Efficacy].

PURPOSE
Enzalutamide is a potent inducer of cytochrome P450 substrates. Hence, it induces major metabolizing enzyme effects in some of the concomitant drugs, raising the possibility of decreased efficacy. We investigated the actual status of drugs for which precautions for co-administration are indicated during concomitant use with enzalutamide.


METHODS
We retrospectively investigated the duration of enzalutamide use, concomitant medications, laboratory values, and events using the medical records of patients prescribed enzalutamide for castration-resistant prostate cancer at the National Cancer Center Hospital from May 2014 to May 2017.


RESULTS
The median age of the 107 studied patients was 74 years[range: 53-93], median duration of enzalutamide prescriptions was 120 days[range: 14-1,008], and the median number of concomitant medications(components)was 6[range: 0-16]. Sixty nine patients(64%)were taking drugs that could be affected by enzyme induction. The medications listed in the concomitant use section of the package insert were warfarin(3 patients) and omeprazole(2 patients). In this study, 4 patients(except for 1 on warfarin)were taking other drugs that could be affected by enzyme induction. Events considered to possibly reduce their efficacy during concomitant use with enzalutamide were elevated blood pressure and blood clots.


CONCLUSIONS
When enzalutamide is used in combination with other drugs, there exists the possibility that the effect of concomitant medications may be weakened by enzyme induction.