Dosing and uses of Zytiga (abiraterone)
Adult dosage forms and strengths
tablet
- 250mg
Prostate Cancer
Indicated for treatment of metastatic castration-resistant prostate cancer (CRPC) in patients who are chemotherapy-naive or in those who have received prior chemotherapy containing docetaxel; administer with prednisone
4 tabs (1000 mg) PO qDay with prednisone 5 mg PO q12hr
Dosage modifications
Coadministration with strong CYP3A4 inducers: Avoid if possible; if must be coadministered, increase dosage frequency of abiraterone from qDay to BID (eg, from 1,000 mg qDay to 1,000 mg BID)
Reduce the dose back to the previous dose and frequency, if the concomitant strong CYP3A4 inducer is discontinued
Renal Impairment
Dose adjustment not required
Hepatic Impairment
Baseline LFTs
- Mild (Child-Pugh A): Dose adjustment not required
- Moderate (Child-Pugh B): Reduce starting dose to 250 mg PO qDay
- Severe (Child-Pugh C): Avoid use; not studied in this population and no dose adjustment can be predicted
Increased LFT during treatment
- Interrupt treatment; may reinitiate at reduced dose of 750 mg PO qDay following return of LFTs to baseline or to AST/ALT ≤2.5 xULN and total bilirubin ≤1.5 xULN
- For patients who resume treatment, monitor serum transaminases and bilirubin at least q2Weeks for 3 months, and then monthly thereafter
- If hepatotoxicity recurs at 750 mg/day, may restart at 500 mg/day (after LFTs decrease as above)
- If hepatoxicity recurs at reduced dose of 500 mg/day, discontinue treatment
Administration
Take on empty stomach, at least 1 hr ac or 2 hr pc
Food increases AUC up to 10-fold
Swallow tablets whole with water; do not chew, crush or split
Pediatric dosage forms and strengths
Not indicated
Geriatric dosage forms and strengths
Of the total number of patients in a phase 3 trial, 71% of patients were 65 yr or older and 28% were 75 yr or older
No overall differences in safety or effectiveness were observed between these elderly patients and younger patients
Metastatic castration-resistant prostate cancer
4 tabs (1000 mg) PO qDay with prednisone 5 mg PO q12hr
Zytiga (abiraterone) adverse (side) effects
>10%
Joint swelling/discomfort (30%)
Hypokalemia (28%; all grades)
Edema (27%)
Muscle discomfort (26%)
Hypophosphatemia (24%; all grades)
Hot flush (19%)
Diarrhea (18%)
Urinary tract infection (12%)
Cough (11%)
1-10%
Hypertension (9%)
Arrhythmia (7%)
Urinary frequency (7%)
Hypophosphatemia (7%; grade 3-4)
Nocturia (6%)
Dyspepsia (6%)
Fractures (5.9%)
Hypokalemia (5%; grade 3-4)
Upper respiratory tract infection (5%)
Chest pain/discomfort (4%)
Cardiac failure (2%)
Hepatotoxicity (2%)
Postmarketing Reports
Respiratory, thoracic and mediastinal disorders: Noninfectious pneumonitis
Rhabdomyolysis
Myopathy
Acute hepatic failure
Warnings
Contraindications
Hypersensitivity
Women who are or may become pregnant
Cautions
Not for use in patients with preexisting severe hepatic impairment (Child-Pugh class C)
Mineralocorticoid excess: caution in patients with a history of cardiovascular disease; safety in patients with LVEF <50% or NYHA Class III or IV heart failure is not established
Hypertension, hypokalemia, and fluid retention may result from increased mineralocorticoid due to CYP17 inhibition; control hypertension and correct hypokalemia before treatment; monitor blood pressure, serum potassium, and symptoms of fluid retention at least monthly
Monitor for symptoms and signs of adrenocortical insufficiency; increased corticosteroid dosage may be indicated before, during, and after stressful situations; concurrent infection or interruption of daily corticosteroids associated with adrenocortical insufficiency
Hepatotoxicity: Increases in liver enzymes have led to drug interruption, dose modification, and/or discontinuation (typically within the first 3 months of threatment); monitor liver function and modify, interrupt, or discontinue dosing as recommended
Strong inhibitor of CYP1A2 and CYP2D6; moderate inhibitor of CYP2C9, CYP2C19, and CYP3A4
CYP3A4 substrate (in vitro); avoid or use caution with drugs that are strong inhibitors or inducers of CYP3A4
Pregnancy and lactation
Pregnancy category: X
Lactation: Unknown whether distributed in breast milk; do not use, not indicated for use in women
Pregnancy categories
A: Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.
B: May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.
C: Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.
D: Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.
X: Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.
NA: Information not available.
Pharmacology of Zytiga (abiraterone)
Mechanism of action
Androgen biosynthesis inhibitor that inhibits 17 alpha-hydroxylase/C17,20-lyase (CYP17); this enzyme is expressed in testicular, adrenal, and prostatic tumor tissues and is required for androgen biosynthesis
Pharmacokinetics
Peak Plasma Time: 2 hr
Peak Plasma Concentration: 226 ng/mL ± 178 ng/mL (at steady state)
AUC: 1173 ± 690 ng.hr/mL; increases up to 10-fold when administered with food
Protein Bound: >99% (albumin, alpha-1 acid glycoprotein)
Vd: 19,669 ± 13,358 L (at steady state)
Not a substrate of P-glycoprotein
Excretion: feces (88%), urine (5%)
Half-life: 12 ± 5 hr (prolonged by hepatic impairment to 18-19 hr)
Metabolism
- Metabolism: Abiraterone acetate is hydrolyzed to abiraterone (active metabolite); hydrolysis is likely via esterase activity and is not CYP mediated; CYP3A4 and SULT2A1 enzymes are involved in the formation of 2 inactive metabolites, N-oxide abiraterone sulphate and abiraterone sulphate
- Enzyme inhibition: Strong inhibitor of CYP1A2 and CYP2D6; moderate inhibitor of CYP2C9, CYP2C19, and CYP3A4
