Enzalutamide, sold under the brand name Xtandi, is a nonsteroidal antiandrogen (NSAA) medication which is used in the treatment of prostate cancer. It is indicated for use in conjunction with castration in the treatment of metastatic castration-resistant prostate cancer (mCRPC) and nonmetastatic castration-resistant prostate cancer. It is taken by mouth. Enzalutamide, sold under the brand name Xtandi, is a nonsteroidal antiandrogen (NSAA) medication which is used in the treatment of prostate cancer. It is indicated for use in conjunction with castration in the treatment of metastatic castration-resistant prostate cancer (mCRPC) and nonmetastatic castration-resistant prostate cancer. It is taken by mouth. Side effects of enzalutamide when added to castration include asthenia, back pain, diarrhea, arthralgia, and hot flashes. Rarely, it can cause seizures. It has a high potential for drug interactions. Enzalutamide is an antiandrogen, and acts as an antagonist of the androgen receptor, the biological target of androgens like testosterone and dihydrotestosterone. In doing so, it prevents the effects of these hormones in the prostate gland and elsewhere in the body. Enzalutamide was first described in 2006, and was introduced for the treatment of prostate cancer in 2012. It was the first second-generation NSAA to be introduced. The medication is available widely throughout the world. Enzalutamide is clinically effective in the treatment of mCRPC. An up to 89% decrease in serum prostate specific antigen (PSA) levels have been reported after a month of taking the drug. PSA level decreased more than 50% in 40 of 65 chemo-naive patients and 38 of 75 chemotherapy-treated patients. Median time to radiographic progression was 56 weeks for chemo-naive patients and 25 weeks for the post-chemotherapy population. Medivation, the developer of enzalutamide, conducted an international phase III trial that began in September 2009 known as AFFIRM. The aim of this trial was determine the safety and effectiveness of enzalutamide in patients who have previously failed chemotherapy treatment with docetaxel. In November 2011, this trial was stopped early after an interim analysis revealed that patients given the drug lived for approximately 5 months longer than those taking placebo. FDA approval was granted in August 2012. Another phase III trial known as PREVAIL is investigating the effectiveness of enzalutamide with patients who have not yet received chemotherapy. On October 22, 2013, Medivation and Astellas announced that the PREVAIL trial met both co-primary endpoints of overall survival, with a 30% reduction in the risk of death compared with placebo (hazard ratio = 0.7; 95% confidence interval, range of 0.59–0.83), and radiographic progression-free survival, with an 81% reduction in risk of radiographic progression or death compared with placebo (hazard ratio = 0.19); 95% confidence interval, 0.15-0.23). In addition, a phase II trial began in March 2011 comparing enzalutamide with bicalutamide in prostate cancer patients who have progressed while on gonadotropin-releasing hormone (GnRH) analogue therapy (e.g., leuprorelin) or surgical castration. Enzalutamide can be used as an antiandrogen in feminizing hormone therapy for transgender women. Enzalutamide is provided in the form of 40 mg Capsule. It is taken orally at a dosage of 160 mg once per day (four capsules). Enzalutamide is contraindicated in women during pregnancy. It may cause fetal harm.