On September 10, 2014, the U.S. Food and Drug Administration (FDA) approved enzalutamide (XTANDI® Capsules, Astellas Pharma U.S., Inc. and Medivation, Inc.) for the treatment of patients with metastatic castration-resistant prostate cancer (mCRPC). Enzalutamide was previously approved in August 2012 for the treatment of patients with metastatic castration-resistant prostate cancer who had prior docetaxel. 

The approval was based on the results of a randomized, double-blind trial in asymptomatic or minimally symptomatic chemotherapy-naïve patients with mCRPC. Patients received either enzalutamide 160 mg orally once daily (N = 871) or placebo (N = 844). Androgen deprivation therapy (GnRH therapy or prior bilateral orchiectomy) was continued during the trial. The co-primary endpoints were overall survival (OS) and radiographic progression-free survival (rPFS) as determined by independent central radiology review. 

The pre-specified interim analysis for OS demonstrated a statistically significant improvement in patients who received enzalutamide [HR = 0.71 (95% CI: 0.60, 0.84); p less than 0.0001] compared to those who received placebo. The median OS was 32.4 and 30.2 months in the enzalutamide and placebo arms, respectively. The OS improvement was supported by a statistically significant prolongation of rPFS in patients who received enzalutamide [HR = 0.17 (95% CI: 0.14, 0.21); p less than 0.0001]. The median rPFS was 3.7 months in the placebo arm and was not yet reached in the enzalutamide arm. A statistically significant improvement in time-to-initiation of cytotoxic chemotherapy was also observed in the enzalutamide arm compared to patients receiving placebo [HR = 0.35 (95% CI: 0.30, 0.40)]. The median time-to-initiation of cytotoxic chemotherapy was 28.0 and 10.8 months in the enzalutamide and placebo arms, respectively. 

The most common adverse reactions (greater than or equal to 10%) in patients treated with enzalutamide from the two randomized trials were asthenia/fatigue, back pain, decreased appetite, constipation, arthralgia, diarrhea, hot flush, upper respiratory tract infection, peripheral edema, dyspnea, musculoskeletal pain, weight loss, headache, hypertension, and dizziness/vertigo. Seizure was reported in one patient in each arm of the randomized trial of chemotherapy-naïve patients with mCRPC. In a previous trial of patients with mCRPC who had received docetaxel, seizure was reported in 0.9% of patients on enzalutamide and in none of the patients on control.

Two randomized trials, including those in patients previously treated with docetaxel and the chemo-naïve population, were considered for the following adverse reactions of special interest. Falls, including fall-related injuries, occurred in 9% of patients treated with enzalutamide compared to 4% of patients receiving placebo. Hypertension was reported in 11% versus 4% of patients on the enzalutamide and placebo arms, respectively. No patient experienced hypertensive crisis. 

The recommended enzalutamide dose is 160 mg orally daily and can be taken with or without food. Enzalutamide should be discontinued in patients who develop a seizure during treatment. 

Full prescribing information is available online.

Healthcare professionals should report all serious adverse events suspected to be associated with the use of any medicine and device to the FDA’s MedWatch Reporting System by completing an online form, by faxing (800-FDA-0178) or mailing the postage-paid address form provided online, or by telephone (800-FDA-1088).

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