I have been writing in a number of prior blog posts and in answers to comments and questions on the blog that I believe that Xtandi (enzalutamide) is a superior drug compared to Zytiga (abiraterone). A number of people have asked me why I say this, so I have decided to respond to the issue.
The phase III trials for both Xtandi and Zytiga were very similar to each other. In both trials investigators measured the percentage of men who progressed or died against placebo. In this very important measurement Xtandi blew Zytiga out of the water. Only 14% of men taking Xtandi during the trial progressed or died compared to 40% of the men in the placebo group. In the phase III trial of Zytiga 28% of the men progressed or died, compared with 46% on placebo. This figure is very significant, as it appears that almost twice as many men died or progressed in the Zytiga group opposed to the Xtandi group.
I am not ignoring the fact that these two trials were not head-to-head clinical trials, which we will never see, so any comparisons must be taken with a grain of salt.
Then, of course is the other very clear advantage for Xtandi, unlike Zytiga it does not require the concurrent taking of Prednisone, a poorly tolerated steroid that comes with many side effects.
If you look at the sales figures of these two drugs, doctors are beginning to favor Xtandi over Zytiga despite it higher price tag. The medical community is beginning to catch on to the superiority of Xtandi, it has taken them longer than it should have, but they finally are recognizing the superiority of Xtandi.
Even the U.K.’s notoriously tight-fisted National Institute for Health and Care Excellence proposed last December endorsing Xtandi in pre-chemo patients but snubbed Zytiga. This endorsement alone speaks volumes about the superiority of Xtandi
I expect to see Xtandi become the preferred drug. If your doctor suggests that you take Zytiga and prednisone instead of Xtandi stop the conversation and have a heart to heart. Tell your doctor to do their homework and make a better choice.