Abiraterone Acetate - Uses, Dosage, and Side Effects

Overview:

Abiraterone acetate is a new oral agent that directly addresses the hormonal basis of prostate cancer. This inhibits the enzyme CYP17 (cytochrome P450 17A1) that is needed in the synthesis of androgens in the testes as well as in the adrenal gland and the tumor. This assists in decreasing the levels of testosterone in the body, denying the cells cancerous of a basic need for growth. Abiraterone acetate works against prostate cancer by reducing the body’s ability to produce androgens and is most useful in cases of hormone-refractory disease or cancer that is already spread outside the prostate gland (metastatic disease).

Drug Group

Abiraterone Acetate belongs to the drug group known as androgen biosynthesis inhibitors. It works by inhibiting the enzyme CYP17A1, which is involved in the production of androgens (male hormones) in the body. This helps reduce the levels of testosterone, which can stimulate the growth of prostate cancer cells.

Dosage:

• Dosage Form: Oral tablet.

• Strength: 250 mg (milligrams) per tablet.

• Standard Dose: The recommended route is one 250 mg tablet of Abiraterone acetate with 5 mg of Prednisolone twice a day for adults, while the dosage is 1000 mg of Abiraterone acetate a day.

• Dose Modifications: In moderate hepatic impairment (Child-Pugh Class B), Abiraterone acetate the dose may be reduced to 250 mg once per day. This drug is contraindicated in patients who have severe liver disease or dysfunction.

For Patients:

Indications:

Abiraterone acetate is used to treat metastatic castration-resistant prostate cancer (mCRPC) and advanced prostate cancer, often in combination with prednisone or androgen deprivation therapy.

Contraindication:

• Pregnancy: It is advised that Abiraterone acetate should not be used in women, especially when they are pregnant, because the product is hazardous to the fetus. Female patients using this drug of childbearing age should avoid contact with this medication and must discuss contraception methods with their doctor before using this medication.

• Severe Liver Impairment: This drug should not be taken by any patient who has severe liver disease because it may aggravate the disease.

Limitations of Abiraterone Acetate:

The limitations of abiraterone acetate include potential liver toxicity, requiring regular liver function monitoring. It can also cause adrenal insufficiency, fluid retention, and hypertension. It should be used with caution in patients with cardiovascular disease and in those with compromised liver function. Additionally, it may interact with other medications, so careful management is necessary.

How Is Abiraterone Acetate Used for Prostate Cancer?

Abiraterone acetate is used for treating prostate cancer by inhibiting an enzyme called CYP17, which is involved in the production of androgens (male hormones) in the body. Since prostate cancer cells rely on these hormones for growth, abiraterone reduces androgen levels, helping slow the cancer's progression. It is typically given alongside Prednisone to manage side effects and prevent adrenal insufficiency. Abiraterone is used for metastatic castration-resistant prostate cancer (mCRPC) and advanced prostate cancer, often after other treatments have failed.

What Are the Side Effects of Abiraterone Acetate?

Although Abiraterone acetate is useful in prostate cancer, its use is not without side effects.

Common Abiraterone Acetate Side Effects:

• Fatigue and weakness.

• Joint or muscle pain.

• Edema of the lower extremities, which include the legs, ankles, or feet.

• Hot flashes.

• Urinary tract infections.

• Diarrhea or constipation.

• Elevated liver enzymes.

• Hypokalemia, also known as reduced potassium levels.

• High blood pressure.

Serious Side Effects of Abiraterone Acetate (less common but more severe):

• Liver Toxicity: A person experiencing injury to the liver may show symptoms such as jaundice, dark-colored urine, or extreme abdominal pain.

• Heart Issues: Palpitations (rapid, irregular heartbeats felt in the chest), shortness of breath, irregular heartbeat, or chest discomfort often require medical attention, an echocardiogram, or immediate chest pain.

• Bone Fractures: Osteoporosis (weak bones, increased fracture risk condition) is a medical condition that results in fragility fractures resulting from a lowered bone density.

Such side effects of Abiraterone acetate should be observed constantly through blood tests in order for the intervention to be made as early as possible.

What Are the Things to Inform the Doctor Before Taking Abiraterone Acetate?

Before taking abiraterone acetate, inform your doctor if you have:

1. Liver Issues: Abiraterone can affect liver function, so it's important to disclose any history of liver disease.

2. Heart Problems or Hypertension: The drug may cause fluid retention and high blood pressure, so inform your doctor if you have a history of cardiovascular conditions.

3. Adrenal Issues: Abiraterone can cause adrenal insufficiency, so let your doctor know if you have adrenal gland problems.

4. Allergies: Notify your doctor about any allergies, especially to medications.

5. Pregnancy or Breastfeeding: Abiraterone can harm a developing fetus and should not be used during pregnancy or while breastfeeding.

6. Other Medications: Tell your doctor about all other medications, including over-the-counter drugs, herbal supplements, and vitamins, as abiraterone can interact with several drugs, such as corticosteroids, certain antibiotics, and antifungals.

Overdose:

If you suspect an overdose, seek medical attention immediately. Symptoms of overdose may include severe fatigue, nausea, vomiting, or swelling.

Missed Dose:

If you miss a dose, take it as soon as you remember unless it Is close to the time for your next dose. Do not double the dose to make up for a missed one. Always follow the dosing schedule as prescribed by your doctor.

Drug Interactions:

Abiraterone acetate has the potential to interact with various medications due to its metabolism through liver enzymes, primarily CYP3A4. These interactions can impact the drug’s effectiveness or increase the risk of side effects. It is important to inform your healthcare provider about all medications you are taking, including prescription drugs, over-the-counter medications, and supplements. Below are common types of interactions:

1. Corticosteroids: Abiraterone is often co-administered with corticosteroids like prednisone to prevent side effects such as adrenal insufficiency. However, the combination may require careful dose adjustments, as corticosteroids can influence electrolyte balance and blood pressure. Monitoring is essential to avoid complications such as hypokalemia or hypertension.

2. Antifungals: Medications like Ketoconazole or Itraconazole, which inhibit CYP3A4, can increase abiraterone levels in the blood. This may lead to enhanced effects or a higher risk of side effects such as liver toxicity. Dose adjustments of abiraterone may be necessary when co-administered with strong CYP3A4 inhibitors.

3. Antibiotics: Certain antibiotics, such as Rifampin or Rifabutin, are strong CYP3A4 inducers and can significantly reduce the effectiveness of abiraterone by increasing its metabolism. This may result in insufficient androgen suppression and reduced therapeutic benefits.

4. Anticonvulsants: Drugs such as Phenytoin, Carbamazepine, or Phenobarbital can lower biraterone levels by inducing CYP3A4 enzymes, potentially reducing its effectiveness. Alternative anticonvulsants that do not interact with CYP3A4 may be preferred.

5. Blood Thinners (Anticoagulants): Abiraterone can increase the risk of bleeding when taken with anticoagulants such as Warfarin. Close monitoring of blood clotting parameters (e.g., INR) is required to minimize the risk of excessive bleeding.

6. Liver-Enzyme Affecting Drugs: Medications that either inhibit or induce liver enzymes can alter the metabolism of abiraterone. For instance, strong CYP3A4 inhibitors (e.g., grapefruit juice, clarithromycin) increase abiraterone concentrations, while inducers (e.g., St. John’s Wort) decrease their effectiveness.

General Advice: Avoid starting or discontinuing any medications while on abiraterone without consulting your healthcare provider. Additionally, always discuss the use of supplements or herbal products, as they can also interfere with the drug’s metabolism or efficacy. Your doctor may need to adjust dosages or recommend alternatives to prevent adverse interactions.

For Doctors

Clinical Pharmacology: Abiraterone acetate is a targeted therapy designed to inhibit CYP17, a critical enzyme involved in androgen biosynthesis. This enzyme is essential for the production of androgens, which are male hormones that promote the growth of prostate cancer cells. Androgens are synthesized in the adrenal glands, testes, and within the tumor microenvironment. By selectively blocking CYP17, abiraterone acetate reduces androgen production at all these sites, helping to control the progression of androgen-dependent prostate cancer.

Mechanism of Action: CYP17 is a dual-function enzyme involved in two critical steps of androgen production: 17α-hydroxylase and 17,20-lyase activity. By inhibiting both functions of CYP17, Abiraterone acetate significantly decreases androgen precursors, such as dehydroepiandrosterone (DHEA) and androstenedione, which are subsequently converted into testosterone. This reduction in androgen levels deprives prostate cancer cells of the hormones they need to grow and proliferate, leading to slower tumor growth and disease progression.

Pharmacodynamics: The pharmacodynamic effects of abiraterone acetate are observed to be a significant reduction in circulating androgen levels, including testosterone. This decrease leads to reduced stimulation of androgen receptors on prostate cancer cells, ultimately suppressing tumor growth. The drug is particularly effective in metastatic castration-resistant prostate cancer (mCRPC), where cancer cells continue to grow despite medical or surgical castration.

Pharmacokinetics: Abiraterone acetate is administered orally and undergoes rapid conversion to its active form, abiraterone, in the body. The drug’s absorption is influenced by food intake, with high-fat meals increasing its bioavailability significantly. For consistent drug levels, it is recommended to take abiraterone on an empty stomach. The active metabolite is extensively processed in the liver, primarily through the cytochrome P450 enzyme system (CYP3A4), followed by further metabolism by sulfotransferase enzymes (SULT). The elimination half-life of abiraterone is approximately 12-17 hours, allowing for once-daily dosing. The majority of the drug is excreted in feces, with a smaller proportion eliminated through urine. This pharmacokinetic profile highlights the need for cautious use in patients with liver impairment, as they are at higher risk for drug accumulation and toxicity.

Drug Warnings and Precautions

Abiraterone acetate requires careful monitoring for liver toxicity, adrenal insufficiency, hypertension, and fluid retention. It can also affect bone health, increasing the risk of fractures. Patients should be cautious if they have cardiovascular conditions, and regular checks for blood pressure, potassium levels, and liver function are needed. The drug is contraindicated in pregnancy and breastfeeding, and it can interact with other medications, requiring dose adjustments.

Use in Specific Populations:

• Pregnancy: Abiraterone acetate is strictly contraindicated during pregnancy because it can cause harm to a developing fetus by interfering with androgen production, which is critical for fetal development. Female partners of male patients taking abiraterone should use effective contraception during treatment and for at least 3 weeks after the last dose.

• Lactation: Breastfeeding is contraindicated during treatment with abiraterone acetate due to the risk of serious adverse reactions in nursing infants. Women are advised not to breastfeed while taking this medication or for a period after completing treatment.

• Pediatric Population: Abiraterone acetate has not been studied in children or adolescents. There is no established safety, efficacy, or dosing information for its use in individuals under 18 years of age, and it is therefore not indicated for pediatric use.

• Renal Impairment: While abiraterone does not require dose adjustments in patients with mild to moderate renal impairment, caution is advised in cases of severe renal dysfunction due to the lack of comprehensive studies in this population. Clinical monitoring may be needed.

• Hepatic Impairment: Abiraterone is contraindicated in patients with severe hepatic impairment (Child-Pugh Class C) due to an increased risk of drug accumulation and liver toxicity. In patients with mild to moderate hepatic impairment, close monitoring of liver function tests is essential, and dosage adjustments may be required if abnormalities develop.

• Geriatric Population: Elderly patients, particularly those over 65 years of age, may experience a heightened risk of certain side effects, such as high blood pressure, hypokalemia, and fluid retention. Although no specific dosage adjustment is typically necessary, more frequent monitoring may be warranted to manage potential adverse reactions effectively.

Clinical Studies

Clinical studies have shown that Abiraterone acetate, when used in combination with Prednisone, significantly improves progression-free survival and overall survival in patients with metastatic castration-resistant prostate cancer (mCRPC). The drug has demonstrated effectiveness in reducing tumor growth by lowering androgen levels.