2.1 Recommended Dosage

The recommended dose of YONSA is 500 mg (four 125 mg tablets) administered orally once daily in combination with methylprednisolone 4 mg administered orally twice daily.

2.2 Important Administration Instructions

To avoid medication errors and overdose, be aware that YONSA (abiraterone acetate) tablets may have different dosing and food effects than other abiraterone acetate products. Patients receiving YONSA should also receive a gonadotropin-releasing hormone (GnRH) analog concurrently or should have had bilateral orchiectomy.

YONSA tablets must be taken as a single dose once daily with or without food [see Clinical Pharmacology (12.3)].  The tablets should be swallowed whole with water.  Do not crush or chew tablets.

2.3 Dose Modification Guidelines in Hepatic Impairment and Hepatotoxicity

Hepatic Impairment

In patients with baseline moderate hepatic impairment (Child-Pugh Class B), reduce the recommended dose of YONSA to 125 mg once daily.  In patients with moderate hepatic impairment monitor ALT, AST, and bilirubin prior to the start of treatment, every week for the first month, every two weeks for the following two months of treatment and monthly thereafter. If elevations in ALT and/or AST greater than 5X upper limit of normal (ULN) or total bilirubin greater than 3X ULN occur in patients with baseline moderate hepatic impairment, discontinue YONSA and do not re-treat patients with abiraterone acetate [see Use in Specific Populations (8.6) and Clinical Pharmacology (12.3)].

Do not use YONSA in patients with baseline severe hepatic impairment (Child-Pugh Class C).

Hepatotoxicity

For patients who develop hepatotoxicity during treatment with YONSA (ALT and/or AST greater than 5X ULN or total bilirubin greater than 3X ULN), interrupt treatment with YONSA [see Warnings and Precautions (5.3)].  Treatment may be restarted at a reduced dose of 375 mg once daily following return of liver function tests to the patient’s baseline or to AST and ALT less than or equal to 2.5X ULN and total bilirubin less than or equal to 1.5X ULN. For patients who resume treatment, monitor serum transaminases and bilirubin at a minimum of every two weeks for three months and monthly thereafter.

If hepatotoxicity recurs at the dose of 375 mg once daily, re-treatment may be restarted at a reduced dose of 250 mg once daily following return of liver function tests to the patient’s baseline or to AST and ALT less than or equal to 2.5X ULN and total bilirubin less than or equal to 1.5X ULN.

If hepatotoxicity recurs at the reduced dose of 250 mg once daily, discontinue treatment with YONSA. 

Permanently discontinue YONSA for patients who develop a concurrent elevation of ALT greater than 3 x ULN and total bilirubin greater than 2 x ULN in the absence of biliary obstruction or other causes responsible for the concurrent elevation [see Warnings and Precautions (5.3)].

2.4 Dose Modification Guidelines for Strong CYP3A4 Inducers

Avoid concomitant strong CYP3A4 inducers (e.g., phenytoin, carbamazepine, rifampin, rifabutin, rifapentine, phenobarbital) during YONSA treatment.

If a strong CYP3A4 inducer must be co-administered, increase the YONSA dosing frequency to twice a day only during the co-administration period (e.g., from 500 mg once daily to 500 mg twice a day).  Reduce the dose back to the previous dose and frequency, if the concomitant strong CYP3A4 inducer is discontinued [see Drug Interactions (7.1) and Clinical Pharmacology (12.3)].

5.1 Hypokalemia, Fluid Retention, and Cardiovascular Adverse Reactions due to Mineralocorticoid Excess  

YONSA may cause hypertension, hypokalemia, and fluid retention as a consequence of increased mineralocorticoid levels resulting from CYP17 inhibition [see Clinical Pharmacology (12.1)].  Monitor patients for hypertension, hypokalemia, and fluid retention at least once a month. Control hypertension and correct hypokalemia before and during treatment with YONSA.

In the two randomized clinical trials, grade 3 to 4 hypertension occurred in 2% of patients, grade 3 to 4 hypokalemia in 4% of patients, and grade 3 to 4 edema in 1% of patients treated with abiraterone acetate [see Adverse Reactions (6)].

Closely monitor patients whose underlying medical conditions might be compromised by increases in blood pressure, hypokalemia or fluid retention, such as those with heart failure, recent myocardial infarction, cardiovascular disease, or ventricular arrhythmia. In postmarketing experience, QT prolongation and Torsades de Pointes have been observed in patients who develop hypokalemia while taking abiraterone acetate.

The safety of YONSA in patients with left ventricular ejection fraction < 50% or New York Heart Association (NYHA) Class III or IV heart failure (in Study 1) or NYHA Class II to IV heart failure (in Study 2)  has not been established because these patients were excluded from these randomized clinical trials [see Clinical Studies (14)].

5.2 Adrenocortical Insufficiency

Adrenal insufficiency occurred in the two randomized clinical studies in 0.5% of patients taking abiraterone acetate and in 0.2% of patients taking placebo.  Adrenocortical insufficiency was reported in patients receiving abiraterone acetate in combination with a corticosteroid, following interruption of daily steroids and/or with concurrent infection or stress. 

Monitor patients for symptoms and signs of adrenocortical insufficiency, particularly if patients are withdrawn from corticosteroids, have corticosteroid dose reductions, or experience unusual stress.  Symptoms and signs of adrenocortical insufficiency may be masked by adverse reactions associated with mineralocorticoid excess seen in patients treated with YONSA.  If clinically indicated, perform appropriate tests to confirm the diagnosis of adrenocortical insufficiency.  Increased dosage of corticosteroids may be indicated before, during and after stressful situations [see Warnings and Precautions (5.1)].

5.3 Hepatotoxicity

In postmarketing experience, there have been abiraterone acetate-associated severe hepatic toxicity, including fulminant hepatitis, acute liver failure and deaths [see Adverse Reactions (6.2)].

In the two randomized clinical trials, grade 3 or 4 ALT or AST increases (at least 5X ULN) were reported in 4% of patients who received abiraterone acetate, typically during the first 3 months after starting treatment.  Patients whose baseline ALT or AST were elevated were more likely to experience liver test elevation than those beginning with normal values.  Treatment discontinuation due to ALT and AST increases occurred in 1% of patients taking abiraterone acetate. In these clinical trials, no deaths clearly related to abiraterone acetate were reported due to hepatotoxicity events.

Measure serum transaminases (ALT and AST) and bilirubin levels prior to starting treatment with YONSA, every two weeks for the first three months of treatment and monthly thereafter.  In patients with baseline moderate hepatic impairment receiving a reduced YONSA dose of 125 mg, measure ALT, AST, and bilirubin prior to the start of treatment, every week for the first month, every two weeks for the following two months of treatment and monthly thereafter.  Promptly measure serum total bilirubin, AST, and ALT if clinical symptoms or signs suggestive of hepatotoxicity develop.  Elevations of AST, ALT, or bilirubin from the patient's baseline should prompt more frequent monitoring. If at any time AST or ALT rise above five times the ULN, or the bilirubin rises above three times the ULN, interrupt YONSA treatment and closely monitor liver function.

Re-treatment with YONSA at a reduced dose level may take place only after return of liver function tests to the patient’s baseline or to AST and ALT less than or equal to 2.5X ULN and total bilirubin less than or equal to 1.5X ULN [see Dosage and Administration (2.3)].

Permanently discontinue treatment with YONSA for patients who develop a concurrent elevation of ALT greater than 3 x ULN and total bilirubin greater than 2 x ULN in the absence of biliary obstruction or other causes responsible for the concurrent elevation [see Dosage and Administration (2.3)].

The safety of YONSA re-treatment of patients who develop AST or ALT greater than or equal to 20X ULN and/or bilirubin greater than or equal to 10X ULN is unknown.

5.4 Increased Fractures and Mortality in Combination with Radium Ra 223 Dichloride

YONSA plus methylprednisolone is not recommended for use in combination with radium Ra 223 dichloride outside of clinical trials.

The clinical efficacy and safety of concurrent initiation of abiraterone acetate plus a corticosteroid and radium Ra 223 dichloride was assessed in a randomized, placebo-controlled multicenter study in 806 patients with asymptomatic or mildly symptomatic castration-resistant prostate cancer with bone metastases.  The study was unblinded early based on an Independent Data Monitoring Committee recommendation.

At the primary analysis, increased incidences of fractures (28.6% vs 11.4%) and deaths (38.5% vs 35.5%) have been observed in patients who received abiraterone acetate plus a corticosteroid in combination with radium Ra 223 dichloride compared to patients who received placebo in combination with abiraterone acetate plus a corticosteroid. 

5.5 Embryo-Fetal Toxicity

The safety and efficacy of YONSA have not been established in females. Based on animal reproductive studies and mechanism of action, YONSA can cause fetal harm and loss of pregnancy when administered to a pregnant female. In animal reproduction studies, oral administration of abiraterone acetate to pregnant rats during organogenesis caused adverse developmental effects at maternal exposures approximately ≥ 0.03 times the human exposure (AUC) at the recommended dose. Advise males with female partners of reproductive potential to use effective contraception during treatment with YONSA and for 3 weeks after the last dose of YONSA [see Use in Specific Populations (8.1, 8.3)]. YONSA should not be handled by females who are or may become pregnant [see How Supplied/Storage and Handling (16)].

5.6 Hypoglycemia

Severe hypoglycemia has been reported when abiraterone acetate was administered to patients with pre-existing diabetes receiving medications containing thiazolidinediones (including pioglitazone) or repaglinide [see Drug Interactions (7.2)]. Monitor blood glucose in patients with diabetes during and after discontinuation of treatment with YONSA. Assess if antidiabetic drug dosage needs to be adjusted to minimize the risk of hypoglycemia.

6.1 Clinical Trial Experience

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in clinical practice.

Two randomized placebo-controlled, multicenter clinical trials (Study 1 and Study 2) enrolled patients who had metastatic castration-resistant prostate cancer who were using a gonadotropin-releasing hormone (GnRH) agonist or were previously treated with orchiectomy. In both Study 1 and Study 2 abiraterone acetate was administered at a dose equivalent to 500 mg of YONSA daily in combination with a different corticosteroid twice daily in the active treatment arms. Placebo plus corticosteroid was given to control patients.

The most common adverse drug reactions (>10%) reported in the two randomized clinical trials that occurred more commonly (>2%) in the abiraterone acetate arm were fatigue, joint swelling or discomfort, edema, hot flush, diarrhea, vomiting, cough, hypertension, dyspnea, urinary tract infection and contusion.

The most common laboratory abnormalities (>20%) reported in the two randomized clinical trials that occurred more commonly (≥2%) in the abiraterone acetate arm were anemia, elevated alkaline phosphatase, hypertriglyceridemia, lymphopenia, hypercholesterolemia, hyperglycemia, elevated AST, hypophosphatemia, elevated ALT and hypokalemia.

Study 1: Metastatic CRPC Following Chemotherapy

Study 1 enrolled 1195 patients with metastatic CRPC who had received prior docetaxel chemotherapy. Patients were not eligible if AST and/or ALT ≥ 2.5X ULN in the absence of liver metastases. Patients with liver metastases were excluded if AST and/or ALT > 5X ULN.

Table 1 shows adverse reactions on the abiraterone acetate arm in Study 1 that occurred with a ≥2% absolute increase in frequency compared to placebo or were events of special interest. The median duration of treatment with abiraterone acetate with a corticosteroid was 8 months.

Table 1: Adverse Reactions due to Abiraterone Acetate in Study 1

Table 2 shows laboratory abnormalities of interest from Study 1. Grade 3-4 low serum phosphorus (7%) and low potassium (5%) occurred at a greater than or equal to 5% rate in the abiraterone acetate with a corticosteroid arm.

Table 2: Laboratory Abnormalities of Interest in Study 1

Study 2: Metastatic CRPC Prior to Chemotherapy

Study 2 enrolled 1088 patients with metastatic CRPC who had not received prior cytotoxic chemotherapy. Patients were ineligible if AST and/or ALT ≥ 2.5X ULN and patients were excluded if they had liver metastases.

Table 3 shows adverse reactions on the abiraterone acetate arm in Study 2 that occurred in ≥ 5% of patients with a ≥ 2% absolute increase in frequency compared to placebo. The median duration of treatment with abiraterone acetate with a corticosteroid was 13.8 months.

Table 3: Adverse Reactions in ≥5% of Patients on the Abiraterone Acetate Arm in Study 2

Table 4 shows laboratory abnormalities that occurred in greater than 15% of patients, and more frequently (>5%) in the abiraterone acetate arm compared to placebo in Study 2.

Table 4: Laboratory Abnormalities in > 15% of Patients in the Abiraterone Acetate Arm of Study 2

Cardiovascular Adverse Reactions

In the combined data for studies 1 and 2, cardiac failure occurred more commonly in patients treated with abiraterone acetate compared to patients on the placebo arm (2.1% versus 0.7%). Grade 3-4 cardiac failure occurred in 1.6% of patients taking abiraterone acetate and led to 5 treatment discontinuations and 2 deaths. Grade 3-4 cardiac failure occurred in 0.2% of patients taking placebo. There were no treatment discontinuations and one death due to cardiac failure in the placebo group.

In Study 1 and 2, the majority of arrhythmias were grade 1 or 2. There was one death associated with arrhythmia and one patient with sudden death in the abiraterone acetate arms and no deaths in the placebo arms. There were 7 (0.5 %) deaths due to cardiorespiratory arrest in the abiraterone acetate arms and 3 (0.3 %) deaths in the placebo arms. Myocardial ischemia or myocardial infarction led to death in 3 patients in the placebo arms and 2 deaths in the abiraterone acetate arms.

6.2 Postmarketing Experience

The following additional adverse reactions have been identified during post approval use of abiraterone acetate with a different corticosteroid.  Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure.

Respiratory, Thoracic and Mediastinal Disorders: non-infectious pneumonitis.

Musculoskeletal and Connective Tissue Disorders: myopathy, including rhabdomyolysis.

Hepatobiliary Disorders: fulminant hepatitis, including acute hepatic failure and death.

Cardiac Disorders: QT prolongation and Torsades de Pointes (observed in patients who developed hypokalemia or had underlying cardiovascular conditions).

Immune System Disorders – Hypersensitivity: anaphylactic reactions (severe allergic reactions that include, but are not limited to difficulty swallowing or breathing, swollen face, lips, tongue or throat, or an itchy rash (urticaria)).

7.1 Effect of Other Drugs on YONSA

Strong CYP3A4 Inducers

The co-administration of rifampin, a strong CYP3A4 inducer, decreased exposure of abiraterone by 55%.  Avoid concomitant strong CYP3A4 inducers during YONSA treatment.  If a strong CYP3A4 inducer must be co-administered with YONSA, increase the YONSA dosing frequency [see Dosage and Administration (2.4) and Clinical Pharmacology (12.3)].

7.2 Effect of YONSA on Other Drugs

CYP2D6 Substrates

Abiraterone is an inhibitor of the hepatic drug-metabolizing enzymes CYP2D6.  The co-administration of YONSA with CYP2D6 substrates increases the concentration of the CYP2D6 substrate, which may increase the frequency and/or severity of adverse reactions of these substrates. Avoid co-administration of abiraterone acetate with substrates of CYP2D6 with a narrow therapeutic index. If alternative treatments cannot be used, consider a dose reduction of the concomitant CYP2D6 substrate drug in accordance with its Prescribing Information [see Clinical Pharmacology (12.3)].

CYP2C8 Substrates

Abiraterone is an inhibitor of the hepatic drug-metabolizing enzymes CYP2D6 and CYP2C8. The co-administration of YONSA with CYP2C8 substrates increases the concentration of the CYP2C8 substrate, which may increase the frequency and/or severity of adverse reactions of these substrates. Therefore, patients should be monitored closely for signs of toxicity related to a CYP2C8 substrate with a narrow therapeutic index if used concomitantly with abiraterone acetate [see Clinical Pharmacology (12.3)].

8.1 Pregnancy

Risk Summary

The safety and efficacy of YONSA have not been established in females. Based on findings from animal studies and the mechanism of action, YONSA can cause fetal harm and potential loss of pregnancy.

There are no human data on the use of YONSA in pregnant women.  In animal reproduction studies, oral administration of abiraterone acetate to pregnant rats during organogenesis, caused adverse developmental effects at maternal exposures of approximately ≥ 0.03 times the human exposure (AUC) at the recommended dose (see Data).

Data

Animal Data

In an embryo-fetal developmental toxicity study in rats, abiraterone acetate caused developmental toxicity when administered at oral doses of 10, 30 or 100 mg/kg/day throughout the period of organogenesis (gestational days 6-17).  Findings included embryo-fetal lethality (increased post implantation loss and resorptions and decreased number of live fetuses), fetal developmental delay (skeletal effects) and urogenital effects (bilateral ureter dilation) at doses >10 mg/kg/day, decreased fetal ano-genital distance at >30 mg/kg/day, and decreased fetal body weight at 100 mg/kg/day.  Doses >10 mg/kg/day caused maternal toxicity.  The doses tested in rats resulted in systemic exposures (AUC) approximately 0.03, 0.1 and 0.3 times, respectively, the AUC in patients.

8.2 Lactation

Risk Summary

The safety and efficacy of YONSA have not been established in females.  There is no information available on the presence of abiraterone acetate in human milk, or on the effects on the breastfed child or milk production.

8.3 Females and Males of Reproductive Potential

Contraception

Males

Based on findings in animal reproduction studies and its mechanism of action, advise male patients with female partners of reproductive potential to use effective contraception during treatment and for 3 weeks after the last dose of YONSA [see Use in Specific Populations (8.1)]. 

Infertility

Based on animal studies, abiraterone acetate may impair reproductive function and fertility in males of reproductive potential [see Nonclinical Toxicology (13.1)].

8.4 Pediatric Use

Safety and effectiveness of abiraterone acetate in pediatric patients have not been established.

8.5 Geriatric Use

Of the total number of patients receiving abiraterone acetate in the two randomized trials, 73% of patients were 65 years and over and 30% were 75 years and over.  No overall differences in safety or effectiveness were observed between these elderly patients and younger patients.  Other reported clinical experience has not identified differences in responses between the elderly and younger patients, but greater sensitivity of some older individuals cannot be ruled out.

8.6 Hepatic Impairment

The pharmacokinetics of abiraterone were examined in subjects with baseline mild (N=8) or moderate (N=8) hepatic impairment (Child-Pugh Class A and B, respectively) and in 8 healthy control subjects with normal hepatic function.  The systemic exposure (AUC) of abiraterone after a single oral dose equivalent to 500 mg of YONSA increased by approximately 1.1-fold and 3.6-fold in subjects with mild and moderate baseline hepatic impairment, respectively compared to subjects with normal hepatic function.

In another trial, the pharmacokinetics of abiraterone were examined in subjects with baseline severe (N=8) hepatic impairment (Child-Pugh Class C) and in 8 healthy control subjects with normal hepatic function.  The systemic exposure (AUC) of abiraterone increased by approximately 7-fold and the fraction of free drug increased 2-fold in subjects with severe baseline hepatic impairment compared to subjects with normal hepatic function.

No dosage modification is recommended for patients with baseline mild hepatic impairment (Child-Pugh Class A).  In patients with baseline moderate hepatic impairment (Child-Pugh Class B), reduce the recommended dose of YONSA to 125 mg once daily.  Do not use YONSA in patients with baseline severe hepatic impairment (Child-Pugh Class C).  If elevations in ALT or AST >5X ULN or total bilirubin >3X ULN occur in patients with baseline moderate hepatic impairment, discontinue abiraterone acetate treatment [see Dosage and Administration (2.3) and Clinical Pharmacology (12.3)].

For patients who develop hepatotoxicity during treatment, interruption of treatment and dosage adjustment may be required [see Dosage and Administration (2.3), Warnings and Precautions (5.3), and Clinical Pharmacology (12.3)].

8.7 Renal Impairment

No dosage modification is recommended for patients with renal impairment [see Clinical Pharmacology (12.3)].

12.1 Mechanism of Action

Abiraterone acetate (YONSA) is converted in vivo to abiraterone, 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 [see Warnings and Precautions (5.1)].

Androgen sensitive prostatic carcinoma responds to treatment that decreases androgen levels.  Androgen deprivation therapies, such as treatment with GnRH agonists or orchiectomy, decrease androgen production in the testes but do not affect androgen production by the adrenals or in the tumor.

Abiraterone acetate decreased serum testosterone and other androgens in patients in the placebo-controlled clinical trial. It is not necessary to monitor the effect of YONSA on serum testosterone levels.

Changes in serum prostate specific antigen (PSA) levels may be observed but have not been shown to correlate with clinical benefit in individual patients.

12.2 Pharmacodynamics

In a clinical study in patients with metastatic CRPC who were treated with YONSA 500 mg once daily and methylprednisolone 4 mg twice daily for 84 days, the average serum testosterone level ± standard deviation (SD) on days 9 and 10 of treatment was 0.33 ± 0.09 ng/dL.

Cardiac Electrophysiology

In a multi-center, open-label, single-arm trial, 33 patients with metastatic CRPC received a dose of 1,000 mg once daily orally of another abiraterone acetate product at least 1 hour before or 2 hours after a meal in combination with a different corticosteroid orally twice daily.  Assessments up to Cycle 2 Day 2 showed no large changes in the QTc interval (i.e., >20 ms) from baseline. However, small increases in the QTc interval (i.e., <10 ms) due to abiraterone acetate cannot be excluded due to study design limitations.

12.3 Pharmacokinetics

Following administration of abiraterone acetate, the pharmacokinetics of abiraterone have been studied in healthy subjects and in patients with metastatic CRPC. In vivo, abiraterone acetate is converted to abiraterone.  In clinical studies of other abiraterone acetate formulations, abiraterone acetate plasma concentrations were below detectable levels (< 0.2 ng/mL) in > 99% of the analyzed samples.

Geometric mean ±SD abiraterone Cmax was 73 ± 44 ng/mL and AUC0-∞ was 373 ± 249 ng·hr/mL following a single dose of YONSA 500 mg in overnight fasted healthy subjects. Dose proportionality was observed in single doses of YONSA in a range of 125 mg to 625 mg.

Absorption

Following oral administration of YONSA to patients with metastatic CRPC, the median time to reach maximum plasma abiraterone concentrations is 2 hours.

Effect of Food

Abiraterone Cmax was approximately 6.5-fold higher and AUC0-∞ was 4.4-fold higher when a single dose of YONSA 500 mg was administered with a high-fat meal (56-60% fat, 900-1,000 calories) compared to overnight fasting in healthy subjects.

YONSA can be taken with or without food.

Distribution

Abiraterone is highly bound (>99%) to the human plasma proteins, albumin and alpha-1 acid glycoprotein.  The apparent steady-state volume of distribution (mean ± SD) is 19,669 ± 13,358 L.

Elimination

In patients with metastatic CRPC, the mean terminal half-life of abiraterone in plasma (mean ± SD) is 12 ± 5 hours.

Metabolism

Following oral administration of 14C-abiraterone acetate as capsules, abiraterone acetate is hydrolyzed to abiraterone (active metabolite).  The conversion is likely through esterase activity (the esterases have not been identified) and is not CYP mediated.  The two main circulating metabolites of abiraterone in human plasma are abiraterone sulphate (inactive) and N-oxide abiraterone sulphate (inactive), which account for about 43% of exposure each.  CYP3A4 and SULT2A1 are the enzymes involved in the formation of N-oxide abiraterone sulphate and SULT2A1 is involved in the formation of abiraterone sulphate.

Excretion

Following oral administration of 14C-abiraterone acetate, approximately 88% of the radioactive dose is recovered in feces and approximately 5% in urine.  The major compounds present in feces are unchanged abiraterone acetate and abiraterone (approximately 55% and 22% of the administered dose, respectively).

Specific Populations

Patients with Hepatic Impairment

The pharmacokinetics of abiraterone was examined in subjects with baseline mild (N=8) or moderate (N=8) hepatic impairment (Child-Pugh Class A and B, respectively) and in 8 healthy control subjects with normal hepatic function.  Systemic exposure to abiraterone after a single oral 1,000 mg dose of another abiraterone acetate product given under fasting conditions increased approximately 1.1-fold and 3.6-fold in subjects with mild and moderate baseline hepatic impairment, respectively.  The mean half-life of abiraterone is prolonged to approximately 18 hours in subjects with mild hepatic impairment and to approximately 19 hours in subjects with moderate hepatic impairment. 

In another trial, the pharmacokinetics of abiraterone were examined in subjects with baseline severe (N=8) hepatic impairment (Child-Pugh Class C) and in 8 healthy control subjects with normal hepatic function.  The systemic exposure (AUC) of abiraterone increased by approximately 7-fold in subjects with severe baseline hepatic impairment compared to subjects with normal hepatic function.  In addition, the mean protein binding was found to be lower in the severe hepatic impairment group compared to the normal hepatic function group, which resulted in a two-fold increase in the fraction of free drug in patients with severe hepatic impairment.

Patients with Renal Impairment

The pharmacokinetics of abiraterone were examined in patients with end-stage renal disease (ESRD) on a stable hemodialysis schedule (N=8) and in matched control subjects with normal renal function (N=8).  In the ESRD cohort of the trial, a single 1,000 mg dose of another abiraterone acetate product was given under fasting conditions 1 hour after dialysis, and samples for pharmacokinetic analysis were collected up to 96 hours post dose.  Systemic exposure to abiraterone after a single oral 1,000 mg dose of another abiraterone acetate product did not increase in subjects with end-stage renal disease on dialysis, compared to subjects with normal renal function.

Drug Interactions Studies

Clinical Studies

Effect of Other Drugs on Abiraterone

Strong CYP3A4 inducers: In a clinical pharmacokinetic interaction study of healthy subjects, pretreated with a strong CYP3A4 inducer (rifampin, 600 mg daily for 6 days) followed by a single dose of 1,000 mg of another abiraterone acetate product that is dose equivalent to a single YONSA 500 mg dose, the mean plasma AUC∞ of abiraterone was decreased by 55%.

Strong CYP3A4 inhibitors: Co-administration of ketoconazole, a strong inhibitor of CYP3A4, had no clinically meaningful effect on the pharmacokinetics of abiraterone.

Effect of Abiraterone on Other Drugs

CYP2D6 substrates: The Cmax and AUC of dextromethorphan (CYP2D6 substrate) were increased 2.8- and 2.9-fold, respectively when dextromethorphan 30 mg was given with another abiraterone acetate product of 1,000 mg daily that is dose equivalent to YONSA 500 mg daily. The AUC for dextrorphan, the active metabolite of dextromethorphan, increased approximately 1.3 fold.

CYP1A2 substrates: When another abiraterone acetate product of 1,000 mg daily that is dose equivalent to YONSA 500 mg daily was given with a single dose of 100 mg theophylline (CYP1A2 substrate), no increase in systemic exposure of theophylline was observed.

CYP2C8 substrates: The AUC of pioglitazone (CYP2C8 substrate) was increased by 46% when pioglitazone was given to healthy subjects with a single dose of 1,000 mg of another abiraterone acetate product that is dose equivalent to a single YONSA 500 mg dose.

In Vitro Studies

Cytochrome P450 (CYP) Enzymes: Abiraterone is a substrate of CYP3A4 and has the potential to inhibit CYP1A2, CYP2D6, CYP2C8 and to a lesser extent CYP2C9, CYP2C19 and CYP3A4/5.

Transporter Systems: In vitro studies show that at clinically relevant concentrations, abiraterone acetate and abiraterone are not substrates of P-glycoprotein (P-gp) and that abiraterone acetate is an inhibitor of P-gp. In vitro, abiraterone and its major metabolites were shown to inhibit the hepatic uptake transporter OATP1B1.  There are no clinical data available to confirm transporter based interaction.

13.1 Carcinogenesis, Mutagenesis, and Impairment of Fertility

A two-year carcinogenicity study was conducted in rats at abiraterone acetate oral doses of 5, 15, and 50 mg/kg/day for males and 15, 50, and 150 mg/kg/day for females.  Abiraterone acetate increased the combined incidence of interstitial cell adenomas and carcinomas in the testes at all dose levels tested.  This finding is considered to be related to the pharmacological activity of abiraterone.  Rats are regarded as more sensitive than humans to developing interstitial cell tumors in the testes.  Abiraterone acetate was not carcinogenic in female rats at exposure levels up to 0.8 times the human clinical exposure based on AUC.  Abiraterone acetate was not carcinogenic in a 6-month study in the transgenic (Tg.rasH2) mouse.

Abiraterone acetate and abiraterone was not mutagenic in an in vitro microbial mutagenesis (Ames) assay or clastogenic in an in vitro cytogenetic assay using primary human lymphocytes or an in vivo rat micronucleus assay.

In repeat-dose toxicity studies in male rats (13- and 26-weeks) and monkeys (39-weeks), atrophy, aspermia/hypospermia, and hyperplasia in the reproductive system were observed at ≥ 50 mg/kg/day in rats and ≥ 250 mg/kg/day in monkeys and were consistent with the antiandrogenic pharmacological activity of abiraterone.  These effects were observed in rats at systemic exposures similar to humans and in monkeys at exposures approximately 0.6 times the AUC in humans.

In a fertility study in male rats, reduced organ weights of the reproductive system, sperm counts, sperm motility, altered sperm morphology and decreased fertility were observed in animals dosed for 4 weeks at ≥ 30 mg/kg/day orally.  Mating of untreated females with males that received 30 mg/kg/day oral abiraterone acetate resulted in a reduced number of corpora lutea, implantations and live embryos and an increased incidence of pre-implantation loss.  Effects on male rats were reversible after 16 weeks from the last abiraterone acetate administration.

In a fertility study in female rats, animals dosed orally for 2 weeks until day 7 of pregnancy at > 30 mg/kg/day had an increased incidence of irregular or extended estrous cycles and pre-implantation loss (300 mg/kg/day).  There were no differences in mating, fertility, and litter parameters in female rats that received abiraterone acetate.  Effects on female rats were reversible after 4 weeks from the last abiraterone acetate administration.

The dose of 30 mg/kg/day in rats is approximately 0.6 times the recommended dose of 500 mg of YONSA/day based on body surface area.

In 13- and 26-week studies in rats and 13- and 39-week studies in monkeys, a reduction in circulating testosterone levels occurred with abiraterone acetate at approximately one half the human clinical exposure based on AUC. As a result, decreases in organ weights and toxicities were observed in the male and female reproductive system, adrenal glands, liver, pituitary (rats only), and male mammary glands. The changes in the reproductive organs are consistent with the antiandrogenic pharmacological activity of abiraterone acetate.

13.2 Animal Toxicology and/or Pharmacology

A dose-dependent increase in cataracts was observed in rats after daily oral abiraterone acetate administration for 26 weeks starting at ≥ 50 mg/kg/day (similar to the human clinical exposure based on AUC).  In a 39-week monkey study with daily oral abiraterone acetate administration, no cataracts were observed at higher doses (2 times greater than the clinical exposure based on AUC).