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Drug Monographs
Treatment Regimens
Scientific Name:
ABIRATERONE
Brand Name(s):
Zytiga

Drug Monograph

Pharmacology

Mechanism of Action

Abiraterone is an androgen biosynthesis inhibitor, that inhibits 17 α-hydroxylase/C17,20-lyase (CYP17). This enzyme is expressed in testicular, adrenal, and prostatic tumor tissues and is required for androgen biosynthesis.
CYP17 catalyzes two sequential reactions: 1) the conversion of pregnenolone and progesterone to their 17α-hydroxy derivatives by 17α-hydroxylase activity and 2) the subsequent formation of dehydroepiandrosterone (DHEA) and androstenedione, respectively, by C17, 20 lyase activity. DHEA and androstenedione are androgens and are precursors of testosterone. Inhibition of CYP17 by abiraterone can also result in increased mineralocorticoid production by the adrenals.

Pharmacokinetics

Oral Absorption: good oral absorption
Median time to maximum plasma abiraterone concentration = 2 hours
Cmax = 226 ± 178 ng/mL (steady-state mean ± SD) and AUC = 1173 ± 690 ng.hr/mL.  Abiraterone accumulation at steady-state is 2-fold higher with continuous dosing versus a single dose.
Abiraterone Cmax and AUC0-∞ approximately 7- and 5-fold higher when administered with a low-fat meal (7% fat, 300 calories) and approximately 17- and 10-fold higher when administered with a high-fat (57% fat, 825 calories) meal.
Distribution: Abiraterone acetate and abiraterone are not substrates of P-glycoprotein (P-gp); abiraterone acetate is an inhibitor of P-gp.
Cross blood brain barrier?  No information
Vd:  19,669 ± 13,358 L   PPB:  Highly bound (>99%) to the human plasma proteins, albumin and alpha-1 acid glycoprotein
Metabolism:  Hepatic; abiraterone acetate is hydrolyzed to abiraterone (active metabolite) likely through esterase activity and not CYP
metabolite(s):  abiraterone sulphate (inactive) via SULT2A1; N-oxide abiraterone sulphate (inactive) via CYP3A4 and SULT2A1
Excretion: Feces 88% and urine 5%
t½- 12 ± 5 hours 

Side Effects

Adverse drug reactions are reported for Abiraterone in combination with Prednisone
IMMEDIATE ONSET (hours to days)
* arrhythmia (7%)
   liver function test elevations (ALT or AST increases of > 5X ULN) 2.3%
EARLY ONSET (days to weeks)
   joint swelling or discomfort (30%)#, muscle pain & discomfort (36%)#
   diarrhea (18% )
* adrenal insufficiency (< 1%)
   hypokalemia (28%), peripheral edema (27%)
   hot flush (19%), flu-like symptoms (rare)
   hypertension (20%)#
   urinary tract infection (11%), , urinary frequency (7%), nocturia (6%)#
   cough (10%)#, dyspepsia (6%)#, upper respiratory tract infection (5%)#
* heart failure (2%)
* hepatotoxicity
   hypertriglceridemia, increased serum creatinine
# Adverse effects were almost as common with Prednisone plus placebo

Therapeutics

Approved Indications

Metastatic castration-resistant prostate cancer (CRPC) after chemotherapy containing docetaxel

Routes

Oral

Dosing

Oral:
• 1000 mg PO daily, in combination with 5 mg Prednisone PO daily.

Dose Adjustment Criteria

Hepatic dysfunction:
If ALT and/or AST greater than 5X ULN or total bilirubin greater than 3X ULN, STOP treatment. Once LFTs return to baseline (or AST and ALT less than or equal to 2.5X ULN and total bilirubin less than or equal to 1.5X ULN), restart at 750 mg PO daily.
If hepatotoxicity recurs at the 750 mg dose, restart treatment at 500 mg PO daily once liver function tests return to normal, as above.  If hepatotoxicity recurs at the 500 mg dose, STOP treatment.
Reduce dose to 250 mg PO daily if moderate hepatic impairment (Child-Pugh Class B)
Discontinue if severe hepatic impairment (Child-Pugh Class c)  (Suggested action)

Contraindications

Women who are or may become pregnant

Monitoring

Clinical Monitoring

RECOMMENDED CRITERIA
• If moderate hepatic impairment: liver function tests (ALT, AST, bilirubin) prior to treatment start, weekly for the first month, every two weeks for next two months, then monthly
 • If Abiraterone is restarted after being on hold: liver function tests (ALT, AST, bilirubin) every two weeks for three months and monthly

Significant Interactions

Abiraterone is a cytochrome P-450 2D6 enzyme inhibitor, should be used with caution when given concurrently with any CYP2D6 substrates, such as thioridazine Abiraterone is also a CYP3A4 enzyme substrate, should be used with caution when given concurrently with any strong CYP3A4 inducer (e.g. rifampin, carbamazepine, phenytoin), or strong CYP3A4 inhibitor (e.g. ketoconazole, itraconazole, nefazodone, troleandomycin, clarithromycin, ritonavir, nelfinavir, diltiazem)

Product Information

Commercial Product Description

Brand Name: Zytiga 250 mg tablets

Pharmaceutical Considerations

Tablets
250 mg tablets white to off-white, oval tablets debossed with AA250 on one side.
Store at room temperature 20oC to 25oC (68oF to 77oF)
No food for at least two hours before and for at least one hour after the dose of Abiraterone. Swallow tablets whole with water

Handling Risk Level

Pregnancy XKNOWN HAZARDOUS DRUG
FDA Pregnancy Risk Factor X

  • This drug must be handled using precautions outlined in CCNS Policies for Occupational Safety, Preparing Cancer Chemotherapy and Administering Cancer Chemotherapy

Note

Handling Risk Level:
HAZARD RISK LEVEL 2
FDA Pregnancy Risk Factor X
• This drug must be handled using precautions outlined in CCNS Policies for Preparing Cancer Chemotherapy and Administering Cancer Chemotherapy and the CCNS Standard for Oral Systemic Therapy for Cancer
• Go to "Additional Information" tab (above) for links to CCNS Policies

Guidelines:
Metastatic Castration Resistant Prostate Cancer
NCDF Coverage Criteria
: Abiraterone in combination with prednisone for metastatic CRPC patients with histologically confirmed prostate cancer, ECOG performance status of 0-2 and progression after previous treatment with docetaxel.

pCODR Recommendation: Asymptomatic or mildly symptomatic metastatic castration-resistant prostate cancer (mCRCP) after failure of androgent deprivation therapy (ADT) which generally includes an LHRH agonist or orchiectomy, in patients who have not received prior chemotherapy and who have ECOG performance status of 0 or 1.  October 22, 2013

Visit the Pan-Canadian Oncology Drug Review website (www.pcodr.ca) for the guidelines on abiraterone for metastatic castrate resistant prostate cancer.
• Go to "Additional Information" tab (above) for links to pCODR Reviews

Availability & Funding

Administrative Information (Nova Scotia)

CCNS Provincial Formulary Status- Intermediate Level for ordering Take Home Prescription • Go to "Additional Information" tab (above) for links to Provincial Formulary of Cancer Drugs Pharmacare Formulary Status- Formulary NOTE: It is recommended to limit ordering of this medication to Oral Chemotherapy Preprinted Order, for patient safety.

New Cancer Drug Fund Status (Nova Scotia)

Pharmacare funding approved for: • Treatment of metastatic prostate cancer (when funding available)