You should check the Internet for a more detailed description, but, briefly, plenaxis is an injectable drug that is similar to Lupron or Zoladex, except that it does not cause an increase in testosterone levels (“flare response”) before lowering them. Thus, it is possible to give it without using an antiandrogen, such as Casodex or Flutamide to block the testosterone “flare” response that occurs during the first 10 days or so after an injection. It probably would have been a significant improvement over the drugs currently used; however, the disadvantage is that relatively large quantities of the drug have to be injected, and some patients have had a severe allergic reaction to it. The FDA has approved its use when other drugs cannot be used.