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Mechanism of Action
CASODEX (bicalutamide) is a non-steroidal androgen receptor inhibitor. It competitively inhibits the action of androgens by binding to cytosol androgen receptors in the target tissue. Prostatic carcinoma is known to be androgen sensitive and responds to treatment that counteracts the effect of androgen and/or removes the source of androgen.
When CASODEX (bicalutamide) is combined with luteinizing hormone releasing hormone (LHRH) analog therapy, the suppression of serum testosterone induced by the LHRH analog is not affected. However, in clinical trials with CASODEX (bicalutamide) as a single agent for prostate cancer, rises in serum testosterone and estradiol have been noted.
In a subset of patients who have been treated with CASODEX (bicalutamide) and an LHRH agonist, and who discontinue CASODEX (bicalutamide) therapy due to progressive advanced prostate cancer, a reduction in Prostate Specific Antigen (PSA) and/or clinical improvement (antiandrogen withdrawal phenomenon) may be observed.
Bicalutamide is well-absorbed following oral administration, although the absolute bioavailability is unknown. Co-administration of bicalutamide with food has no clinically significant effect on rate or extent of absorption.
Bicalutamide is highly protein-bound (96%) [see DRUG INTERACTIONS].
Bicalutamide undergoes stereospecific metabolism. The S (inactive) isomer is metabolized primarily by glucuronidation. The R (active) isomer also undergoes glucuronidation but is predominantly oxidized to an inactive metabolite followed by glucuronidation. Both the parent and metabolite glucuronides are eliminated in the urine and feces. The S-enantiomer is rapidly cleared relative to the R-enantiomer, with the R-enantiomer accounting for about 99% of total steady-state plasma levels.
Pharmacokinetics of the active enantiomer of CASODEX (bicalutamide) in normal males and patients with prostate cancer are presented in Table 3.
|Normal Males (n=30)|
|Apparent Oral Clearance (L/hr)||0.320||0.103|
|Single Dose Peak Concentration (µg/mL)||0.768||0.178|
|Single Dose Time to Peak Concentration (hours)||31.3||14.6|
|Patients with Prostate Cancer (n=40)|
CASODEX (bicalutamide) 50 mg Daily in Combination with an LHRH-A
In a multicenter, double-blind, controlled clinical trial, 813 patients with previously untreated advanced prostate cancer were randomized to receive CASODEX (bicalutamide) 50 mg once daily (404 patients) or flutamide 250 mg (409 patients) three times a day, each in combination with LHRH analogs (either goserelin acetate implant or leuprolide acetate depot).
In an analysis conducted after a median follow-up of 160 weeks was reached, 213 (52.7%) patients treated with CASODEX (bicalutamide) -LHRH analog therapy and 235 (57.5%) patients treated with flutamide-LHRH analog therapy had died. There was no significant difference in survival between treatment groups (see Figure 1). The hazard ratio for time to death (survival) was 0.87 (95% confidence interval 0.72 to 1.05).
Figure 1 - The Kaplan-Meier probability of death for both
antiandrogen treatment groups.
There was no significant difference in time to objective tumor progression between treatment groups (see Figure 2).
Objective tumor progression was defined as the appearance of any bone metastases or the worsening of any existing bone metastases on bone scan attributable to metastatic disease, or an increase by 25% or more of any existing measurable extraskeletal metastases. The hazard ratio for time to progression of CASODEX (bicalutamide) plus LHRH analog to that of flutamide plus LHRH analog was 0.93 (95% confidence interval, 0.79 to 1.10).
Figure 2 - Kaplan-Meier curve for time to progression for
both antiandrogen treatment groups.
Quality of life was assessed with self-administered patient questionnaires on pain, social functioning, emotional well being, vitality, activity limitation, bed disability, overall health, physical capacity, general symptoms, and treatment related symptoms. Assessment of the Quality of Life questionnaires did not indicate consistent significant differences between the two treatment groups.
Safety Data from Clinical Studies using CASODEX (bicalutamide) 150 mg
CASODEX (bicalutamide) 150 mg is not approved for use either alone or with other treatments.
Two identical multicenter, randomized, open-label trials comparing CASODEX (bicalutamide) 150 mg daily monotherapy to castration were conducted in patients that had locally advanced (T3-4, NX, MO) or metastatic (M1) prostate cancer.
Monotherapy — M1 Group
CASODEX (bicalutamide) 150 mg daily is not approved for use in patients with M1 cancer of the prostate. Based on an interim analysis of the two trials for survival, the Data Safety Monitoring Board recommended that CASODEX (bicalutamide) treatment be discontinued in the M1 patients because the risk of death was 25% (HR 1.25, 95% CI 0.87 to 1.81) and 31% (HR 1.31, 95% CI 0.97 to 1.77) higher in the CASODEX (bicalutamide) treated group compared to that in the castrated group, respectively.
Locally Advanced (T3-4, NX, MO) Group
CASODEX (bicalutamide) 150 mg daily is not approved for use in patients with locally advanced (T3-4, NX, M0) cancer of the prostate. Following discontinuation of all M1 patients, the trials continued with the T3-4, NX, MO patients until study completion. In the larger trial (N=352), the risk of death was 25% (HR 1.25, 95% CI 0.92 to 1.71) higher in the CASODEX (bicalutamide) group and in the smaller trial (N=140), the risk of death was 36% (HR 0.64, 95% CI, 0.39 to 1.03) lower in the CASODEX (bicalutamide) group.
In addition to the above two studies, there are three other on-going clinical studies that provide additional safety information for CASODEX (bicalutamide) 150 mg, a dose that is not approved for use. These are three multicenter, randomized, double-blind, parallel group trials comparing CASODEX (bicalutamide) 150 mg daily monotherapy (adjuvant to previous therapy or under watchful waiting) with placebo, for death or time to disease progression, in a population of 8113 patients with localized or locally advanced prostate cancer.
CASODEX (bicalutamide) 150 mg daily is not approved for use as therapy for patients with localized prostate cancer who are candidates for watchful waiting. Data from a planned subgroup analysis of two of these trials in 1627 patients with localized prostate cancer who were under watchful waiting, revealed a trend toward decreased survival in the CASODEX (bicalutamide) arm after a median follow-up of 7.4 years. There were 294 (37.7%) deaths in the CASODEX (bicalutamide) treated patients versus 279 (32.9%) deaths in the placebo treated patients (localized watchful waiting group) for a hazard ratio of 1.16 (95% CI 0.99 to 1.37).
*Based on a maximum dose of 50 mg/day of bicalutamide for an average 70 kg patient.
Last reviewed on RxList: 3/13/2009
This monograph has been modified to include the generic and brand name in many instances.
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