The safety and effectiveness of bicalutamide in pediatric patients have not been established.
Bicalutamide orodispersible tablet was studied in combination with anastrozole orodispersible tablet in an open-label, non-comparative, multi-center study that assessed the efficacy and safety of this combination regimen over 12 months in the treatment of gonadotropin-independent precocious puberty in boys with familial male-limited precocious puberty, also known as testotoxicosis. Patients were enrolled in the study if they had a baseline age ≥ 2 years and a diagnosis of testotoxicosis based on clinical features of progressive precocious puberty, symmetrical testicular enlargement, advanced bone age, pubertal levels of serum testosterone, prepubertal pattern of gonadotropin secretion following a GnRH stimulation test, and absence of other clinical and biochemical causes of testosterone excess. Thirteen out of the 14 patients enrolled completed 12 months of combination treatment (one patient was lost to follow-up). If central precocious puberty (CPP) developed, an LHRH analog was to be added. Four patients were diagnosed with CPP during the 12-month study and received LHRH analog treatment and 2 additional patients were diagnosed at the end of the 12 months and received treatment subsequently. Mean ± SD characteristics at baseline were as follows: chronological age: 3.9±1.9 years; bone age 8.8±2.5; bone age/chronological age ratio: 2.06 ± 0.51; growth rate (cm/yr): 10.81 ± 4.22; growth rate standard deviation score (SDS): 0.41 ± 1.36.
The starting bicalutamide dose was 12.5 mg. Bicalutamide was titrated in each patient until steady-state R-bicalutamide (the active isomer of bicalutamide) trough plasma concentration reached 5 to 15 mcg/mL, which is the range of therapeutic concentrations achieved in adults with prostate cancer following the administration of the currently approved bicalutamide dose of 50 mg. The starting daily dose of anastrozole was 0.5 mg. Anastrozole was independently titrated in each patient until it reached at steady-state a serum estradiol concentration of <10 pmol/L (2.7 pg/mL). The following ascending doses were used for bicalutamide: 12.5 mg, 25 mg, 50 mg, and 100 mg. For anastrozole there were two ascending doses: 0.5 mg and 1 mg. At the end of the titration phase, 1 patient was on 12.5 mg bicalutamide, 8 patients were on 50 mg bicalutamide, and 4 patients were on 100 mg bicalutamide; 10 patients were on 0.5 mg anastrozole and 3 patients were on 1 mg anastrozole. In the majority of patients, steady-state trough concentrations of R-bicalutamide appeared to be attained by Day 21 with once daily dosing. Steady-state trough plasma anastrozole concentrations appeared to be attained by Day 8.
The primary efficacy analysis of the study was to assess the change in growth rate after 12 months of treatment, relative to the growth rate during the ≥6 months prior to entering the study. Pre-study growth rates were obtained retrospectively. There was no statistical evidence that the growth rate was reduced during treatment. During bicalutamide /anastrozole treatment the mean growth rate (cm/yr) decreased by 1.6 cm/year, 95% CI (-4.7 to 1.5) p=0.28; the mean growth rate SDS decreased by 0.1 SD, 95% CI (–1.2 to 1.0) p=0.88. Table 2 shows descriptive data for growth rates for the overall population and for subgroups defined by history of previous treatment for testotoxicosis with ketoconazole, spironolactone, anastrozole or other aromatase inhibitors.
Table 2. Growth RatesEndpoint | Analysis population | Pre-study Mean | Change from pre-study to 12 months | % patients with growth reduction Change compared to pre-study growth rate. |
Mean | Median | (Min, Max) | | |
Growth rate (cm/yr) | All treated (n=13) | 10.8 | -1.6 | -2.8 | (-7.4, 8.4) | 9/13 (69%) |
PT PT = Previous treatment for testotoxicosis with ketoconazole, spironolactone, anastrozole or other aromatase inhibitors. (n=6) | 10.3 | -0.2 | -2.6 Median calculated as midpoint of 3rd and 4th ranked observations. | (-7.2, 8.4) | 4/6 (67%) |
NPT NPT = no previous treatment for testotoxicosis with ketoconazole, spironolactone, anastrozole, or other aromatase inhibitors. (n=7) | 11.2 | -2.8 | -2.8 | (-7.4, 1.1) | 5/7 (71%) |
|
Growth rate (SD units) | All treated (n=13) | 0.4 | -0.1 | -0.4 | (-2.7, 3.5) | 9/13 (69%) |
PT (n=6) | -0.1 | +0.7 | -0.2 | (-1.6, 3.5) | 4/6 (67%) |
NPT (n=7) | 0.8 | -0.7 | -0.4 | (-2.7, 0.5) | 5/7 (71%) |
Total testosterone concentrations increased by a mean of 5 mmol/L over the 12 months of treatment from a baseline mean of 10 mmol/L. Estradiol concentrations were at or below the level of quantification (9.81 pmol/L) for 11 of 12 patients after 12 months of treatment. Six of the 12 patients started treatment at an estradiol concentration below the level of quantification.
There were no deaths, serious adverse events, or discontinuations due to adverse events during the study. Of the 14 patients exposed to study treatment, 13 (92.9%) experienced at least one adverse event. The most frequently reported (>3 patients) adverse events were gynecomastia (7/14, 50%), central precocious puberty (6/14, 43%), vomiting (5/14, 36%), headache (3/14, 21%), pyrexia (3/14, 21%), and upper respiratory tract infection (3/14, 21%). Adverse reactions considered possibly related to bicalutamide by investigators included gynecomastia (6/14, 43%), central precocious puberty (2/14, 14%), breast tenderness (2/14, 14%), breast pain (1/14, 7%), asthenia (1/14, 7%), increased alanine aminotransferase [ALT] (1/14, 7%), increased aspartate aminotransferase [AST] (1/14, 7%), and musculoskeletal chest pain (1/14, 7%). Headache was the only adverse reaction considered possibly related to anastrozole by investigators. For the patient who developed elevated ALT and AST, the elevation was <3X ULN, and returned to normal without stopping treatment; there was no concomitant elevation in total bilirubin.