Bicalutamide dosages used in the treatment of prostate cancer

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Abstract
BACKGROUND Androgen deprivation is often used for the treatment of patients with prostate cancer. Androgen deprivation can be achieved by surgical castration or medical castration, with or without using an antiandrogen. Each of these treatments may be used alone, or an antiandrogen may be used alongside castration to produce combined androgen blockade therapy. METHODS The nonsteroidal antiandrogen, bicalutamide (Casodex®), has been evaluated as a component in combined androgen blockade and as monotherapy. We review the arguments that indicate why a 50‐mg once‐daily dose of bicalutamide is appropriate in combined androgen blockade, while ongoing clinical trials evaluate 150‐mg once‐daily as monotherapy in the treatment of prostate cancer. RESULTS The choice of the 50‐mg dose of bicalutamide when used in combined androgen blockade is supported by four main arguments. First, bicalutamide 50 mg is at least equivalent to, if not better than, flutamide 750 mg in terms of receptor affinity, potency, and favorable plasma concentration profile. Second, the reduction in testosterone concentrations produced by medical or surgical castration decreases the potential competition between bicalutamide and testosterone for androgen receptors in prostate cells, allowing the use of a lower dose of antiandrogen in combined androgen blockade than is necessary in monotherapy. Third, bicalutamide 50 mg has an excellent tolerability profile. Fourth, at the 50‐mg dose, bicalutamide plus luteinizing hormone‐releasing hormone analogue was equivalent to flutamide plus luteinizing hormone‐releasing hormone analogue, although there was a trend towards longer survival with bicalutamide. Furthermore, investigations of higher doses of bicalutamide have justified evaluation of bicalutamide 150 mg as monotherapy. First, pharmacodynamic studies reveal an increasing prostate‐specific antigen response with increasing dose, which appears to plateau at a dose of around 150–200 mg. Second, in an analysis with 31% mortality, bicalutamide 150 mg appeared to have equivalent efficacy compared with castration in terms of survival in patients with nonmetastatic prostate cancer. CONCLUSIONS On the basis of available data, bicalutamide 50 mg is an appropriate dose to use in combined androgen blockade, while 150 mg is being evaluated in ongoing clinical trials as a suitable dose for monotherapy. Prostate 39:47–53, 1999.