Which of the following drugs is an antiandrogen?

Casodex, also known by its generic name bicalutamide, is classified as an antiandrogen. Antiandrogens are agents that inhibit the effects of androgens, which are male hormones such as testosterone. This inhibition can be beneficial in conditions where androgen action needs to be reduced, such as prostate cancer.

The mechanism of Casodex involves binding to androgen receptors, thereby blocking the action of testosterone and other androgens. By preventing these hormones from exerting their effects on prostate tissue, Casodex can help slow the progression of androgen-dependent tumors.

In contrast, the other options listed serve different purposes: Leuprolide and Triptorelin are both gonadotropin-releasing hormones (GnRH) analogs that reduce testosterone production by suppressing gonadotropins. Firmagon (degarelix) is a GnRH antagonist that also lowers testosterone levels but does not act directly on androgen receptors like Casodex does. Therefore, Casodex is the correct answer as it directly functions to prevent androgens from influencing cellular activity.