On April 28, 2011, the U.S. Food and Drug Administration approved abiraterone acetate (Zytiga Tablets, Centocor Ortho Biotech, Inc.) for use in combination with prednisone for the treatment of patients with metastatic castration-resistant prostate cancer (mCRPC) who have received prior chemotherapy containing docetaxel.
The approval is based on the results of a randomized, placebo-controlled, multicenter trial in 1195 patients with mCRPC previously treated with docetaxel-containing regimens. Patients were randomly allocated (2:1) to receive either abiraterone acetate orally at a dose of 1000 mg once daily (N=797) or placebo once daily (N=398). Patients in both arms (abiraterone acetate and placebo) received prednisone 5 mg orally twice daily. Treatment continued until disease progression (defined as a 25% increase in PSA over the patient’s baseline/nadir together with protocol-defined radiographic progression and symptomatic or clinical progression), unacceptable toxicity, initiation of new treatment, or withdrawal. Patients with prior ketoconazole treatment for prostate cancer and a history of adrenal gland or pituitary disorders were excluded.
A pre-specified interim overall survival (OS) analysis was performed when 552 events had occurred. This analysis demonstrated a statistically significant improvement in OS in patients receiving abiraterone acetate compared to those on the placebo-containing arm (HR=0.646; 95% CI: 0.543, 0.768; p < 0.0001). The median OS was 14.8 versus 10.9 months in the abiraterone and placebo arm, respectively. An updated OS analysis, conducted after 775 events, demonstrated a median OS of 15.8 versus 11.2 months in the abiraterone acetate and placebo-containing arms, respectively (HR=0.740; 95% CI: 0.638, 0.859).
The most common adverse reactions (> 5%) were joint swelling or discomfort, hypokalemia, edema, muscle discomfort, hot flush, diarrhea, urinary tract infection, cough, hypertension, arrhythmia, urinary frequency, nocturia, dyspepsia and upper respiratory tract infection. The most common adverse drug reactions resulting in drug discontinuation were increased aspartate aminotransferase and/or alanine aminotransferase, urosepsis and cardiac failure (each in < 1% of patients taking abiraterone).
The most common electrolyte imbalances in patients receiving abiraterone were hypokalemia (28%) and hypophosphatemia (24%). Following interruption of daily corticosteroids and/or with concurrent infection or stress, adrenocortical insufficiency (<1%) has been reported in clinical trials in patients receiving abiraterone acetate at the recommended dose in combination with prednisone.
Abiraterone acetate Cmax and exposure were increased up to 17-fold and 10-fold higher, respectively, when a single dose was administered with a meal compared to a fasting state.
The recommended dose and schedule for abiraterone acetate is 1000 mg orally once daily in combination with prednisone 5 mg orally twice daily. Abiraterone acetate should be taken on an empty stomach. No food should be consumed for at least two hours before the dose of abiraterone acetate is taken and for at least one hour after the abiraterone acetate dose.
Full prescribing information, including clinical trial information, safety, dosing, drug-drug interactions and contraindications is available at: http://www.accessdata.fda.gov/drugsatfda_docs/label/2011/202379lbl.pdf 1
Healthcare professionals should report all serious adverse events suspected to be associated with the use of any medicine and device to FDA’s MedWatch Reporting System by completing a form online at http://www.fda.gov/medwatch/report.htm 2, by faxing (1-800-FDA-0178) or mailing the postage-paid address form provided online, or by telephone (1-800-FDA-1088).
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