ABIRATERONE ACETATE tablets
Abiraterone acetate, the active ingredient of abiraterone acetate tablets, USP is the acetyl ester of abiraterone. Abiraterone is an inhibitor of CYP17 (17α-hydroxylase/C17,20-lyase). Each abiraterone acetate tablet contains either 250 mg of abiraterone acetate. Abiraterone acetate is designated chemically as (3β)-17-(3-pyridinyl) androsta-5,16-dien-3-yl acetate.
Abiraterone Acetate USP is a white to off-white, non-hygroscopic, crystalline powder. Its molecular formula is C26 H33 NO2 and it has a molecular weight of 391.55. Abiraterone acetate is a lipophilic compound with an octanol-water partition coefficient of 3.57 and is practically insoluble in water. The pKa at about 25°C is 3.06.
Abiraterone acetate tablets, USP are available in 250 mg uncoated tablets with the following inactive ingredients: colloidal silicon dioxide, croscarmellose sodium, lactose monohydrate, magnesium stearate, microcrystalline cellulose, povidone, and sodium lauryl sulfate.
Indications and usage
Abiraterone acetate tablets are indicated in combination with prednisone for the treatment of patients with Metastatic castration-resistant prostate cancer (CRPC).
Mechanism of Action
Abiraterone acetate 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.
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 placebocontrolled clinical trial. It is not necessary to monitor the effect of abiraterone acetate 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.
Dosage and administration
The recommended dose of abiraterone acetate tablets is 1,000 mg (four 250 mg tablets) orally once daily in combination with prednisone 5 mg administered orally twice daily.
- Patients receiving abiraterone acetate tablets should also receive a gonadotropin-releasing hormone (GnRH) analog concurrently or should have had bilateral orchiectomy. Abiraterone acetate tablets must be taken on an empty stomach, either one hour before or two hours after a meal
- The tablets should be swallowed whole with water. Do not crush or chew tablets.
Hepatic Impairment: In patients with baseline moderate hepatic impairment (Child-Pugh Class B), reduce the recommended dose of abiraterone acetate tablets to 250 mg once daily.
Do not use abiraterone acetate tablets in patients with baseline severe hepatic impairment (Child-Pugh Class C).
Hepatotoxicity: For patients who develop hepatotoxicity during treatment with abiraterone acetate tablets (ALT and/or AST greater than 5× ULN or total bilirubin greater than 3× ULN), interrupt treatment with abiraterone acetate tablets. Treatment may be restarted at a reduced dose of 750 mg once daily following return of liver function tests to the patient’s baseline or to AST and ALT less than or equal to 2.5× ULN and total bilirubin less than or equal to 1.5× ULN. For patients who resume treatment, monitor serum transaminases and bilirubin at a minimum of every two weeks for three months and monthly thereafter.
Dos e Modification Guidelines for Strong CYP3A4 Inducers: Avoid concomitant strong CYP3A4 inducers (e.g., phenytoin, carbamazepine, rifampin, rifabutin, rifapentine, phenobarbital) during abiraterone acetate tablets treatment.
If a strong CYP3A4 inducer must be co-administered, increase the abiraterone acetate tablets dosing frequency to twice a day only during the co-administration period (e.g., from 1,000 mg once daily to 1,000 mg twice a day). Reduce the dose back to the previous dose and frequency, if the concomitant strong CYP3A4 inducer is discontinued.
Pregnancy: Abiraterone acetate can cause fetal harm and potential loss of pregnancy.
Warnings and precautions
Hypertension, Hypokalemia and Fluid Retention Due to Mineralocorticoid
Excess Abiraterone acetate may cause hypertension, hypokalemia, and fluid retention as a consequence of increased mineralocorticoid levels resulting from CYP17 inhibition. Monitor patients for hypertension, hypokalemia, and fluid retention at least once a month. Control hypertension and correct hypokalemia before and during treatment with abiraterone acetate.
Adrenal insufficiency occured in 0.3% of 2230 patients taking abiraterone acetate and in 0.1% of 1763 patients taking placebo in the combined data of randomized, placebo-controlled clinical studies. Adrenocortical insufficiency was reported in patients receiving abiraterone acetate in combination with prednisone, following interruption of daily steroids and/or with concurrent infection or stress.
Hepatotoxicity: In postmarketing experience, there have been abiraterone acetate-associated severe hepatic toxicity, including fulminant hepatitis, acute liver failure and deaths.
Measure serum transaminases (ALT and AST) and bilirubin levels prior to starting treatment with abiraterone acetate, every two weeks for the first three months of treatment and monthly thereafter. In patients with baseline moderate hepatic impairment receiving a reduced abiraterone acetate dose of 250 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 abiraterone acetate treatment and closely monitor liver function.
The most common adverse reactions (≥10%) are fatigue, arthralgia, hypertension, nausea, edema, hypokalemia, hot flush, diarrhea, vomiting, upper respiratory infection, cough, and headache.
The most common laboratory abnormalities (> 20%) are anemia, elevated alkaline phosphatase, hypertriglyceridemia, lymphopenia, hypercholesterolemia, hyperglycemia, and hypokalemia.
Drugs that Inhibit or Induce CYP3A4 Enzymes
Based on in vitro data, abiraterone acetate is a substrate of CYP3A4.
In a dedicated drug interaction trial, co-administration of rifampin, a strong CYP3A4 inducer, decreased exposure of abiraterone by 55%. Avoid concomitant strong CYP3A4 inducers during abiraterone acetate treatment. If a strong CYP3A4 inducer must be co-administered, increase the abiraterone acetate dosing frequency.
In a dedicated drug interaction trial, co-administration of ketoconazole, a strong inhibitor of CYP3A4, had no clinically meaningful effect on the pharmacokinetics of abiraterone.
Effects of Abiraterone on Drug Metabolizing Enzymes
Abiraterone acetate is an inhibitor of the hepatic drug-metabolizing enzyme CYP2D6 and CYP2C8. In a CYP2D6 drug-drug interaction trial, the Cmax and AUC of dextromethorphan (CYP2D6 substrate) were increased 2.8- and 2.9-fold, respectively, when dextromethorphan was given with abiraterone acetate1,000 mg daily and prednisone 5 mg twice daily. Avoid co-administration of abiraterone acetate with substrates of CYP2D6 with a narrow therapeutic index (e.g., thioridazine). If alternative treatments cannot be used, consider a dose reduction of the concomitant CYP2D6 substrate drug.
In a CYP2C8 drug-drug interaction trial in healthy subjects, the AUC of pioglitazone (CYP2C8 substrate) was increased by 46% when pioglitazone was given together with a single dose of 1,000 mg abiraterone acetate. 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.
Use in specific populations
Pregnancy: Based on findings from animal studies and the mechanism of action, abiraterone acetate is contraindicated for use in pregnant women because the drug can cause fetal harm and potential loss of pregnancy. Abiraterone acetateis not indicated for use in females.
Contraception: Based on findings in animal reproduction studies and its mechanism of action, advise males with female partners of reproductive potential to use effective contraception during treatment and for 3 weeks after the final dose of abiraterone acetate.
Infertility: Based on animal studies, abiraterone acetate may impair reproductive function and fertility in males of reproductive potential.
Pediatric Use: Safety and effectiveness of abiraterone acetate in pediatric patients have not been established.
Geriatric Use: Of the total number of patients receiving abiraterone acetate in randomized clinical trials, 70%of patients were 65 years and over and 27% 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.
Patients with Renal Impairment: No dosage adjustment is necessary for patients with renal impairment.
Human experience of overdose with abiraterone acetate is limited.
There is no specific antidote. In the event of an overdose, stop abiraterone acetate, undertake general supportive measures, including monitoring for arrhythmias and cardiac failure and assess liver function.