ZYTIGA 

Description

Zytiga is a derivative of androstane, which involves in the prohibition process of steroid 17 alpha hydroxylase and containing anti-neoplastic activity and it is an oral tablet which is an active acetate ester form of steroidal compound known as Abiraterone with anti-androgenic activity.

Indication of Zytiga

The Zytiga tablets are indicated for;

Metastatic castration resistance prostate cancer

Metastatic high-risk castration sensitive prostate cancer

Mechanism of Zytiga

Abiraterone acetate is a prodrug form, after oral administration which get converted into Abiraterone inside the body

Abiraterone, an active form which expels its action on androgen biosynthesis by prohibiting an enzyme called 17 alpha hydroxylase/C17, 20-lyase (CYP17).

This enzyme is important for androgen biosynthesis which is expressed in testicular, adrenal & prostatic cancer cells.

A CYP17 enzyme activates two consecutive reactions;

1. Transformation of pregnenolone & progesterone to their 17 alpha hydroxy derivatives with the help of 17 alpha hydroxylase.
2. Production of dehydroepiandrosterone & androstenedione, relatively by CYP17, 20 lyase activity.

DHEA & androstenedione are androgens which as messenger of testosterone.

Absorption

High plasma concentration of Zytiga is reaches within 2 hours after drug intake.

Food should not be taken for at least 2 hours earlier the dose of Zytiga or at least one hour after the dose of Zytiga.

Distribution

Zytiga is highly bound to human plasma protein with >99%.

Metabolism

Abiraterone acetate is undergone hydrolysis and leads to change into Abiraterone which an active form is.

Two major circulating metabolites of Abiraterone is;

Abiraterone sulphate

N-oxide Abiraterone sulphate

Excretion

88% of metabolite is excreted through feces; 5% in urine.

The component present in feces is an unchanged form of Abiraterone.

The terminal means half-life of Zytiga is 12 ± 5 hours.

Dosage and administration

In Metastatic CRPC:

The recommended dose of Zytiga is 1000mg (two 500 mg tablets or four 250 mg tablets) should be administered as a once daily with 5mg of prednisolone should be given two times a day

In Metastatic high risk CSPC:

The recommended dose of Zytiga is 1000mg (two 500 mg tablets or four 250 mg tablets) should be administered as a once daily with 5mg of prednisolone should be given two times a day

Dose modification:

In liver impairment patients:

In moderate hepatic damage patients, the dose of Zytiga should be reduced to 250mg as a single dose.

In moderate liver damaged patients, AST & ALT level should be monitored frequently.

In severe liver damaged patients, Zytiga should not be recommended.

Hepatotoxicity:

Patient suffered with liver toxicity, during the treatment Zytiga should be postponed and provide supportive measures.

Therapy should be resumed at reduced dose of 750mg as a single dose.

If liver toxicities reappear with the dose of 750mg, should be retreated with 500mg single dose followed with LFT.

Discontinue the Zytiga therapy permanently, if patients may have current elevation of AST & ALT.

Concurrent use of Zytiga with CYP3A4 inducers:

In case concurrent use of Zytiga with CYP3A4 inducers, the frequency of Zytiga tablets should be increased to two times a day, it may only occur in co administration time.

If co-administration discontinues, then frequency changes to once daily.

Zytiga tablet should be administered on an empty stomach and food not taken for at least 2 hours before the dose or 1 hour after the dose.

Overdosage

The over dose of Zytiga has no specific antidote. Provide supportive measures and Monitor the patients for arrhythmia, cardiac failure & determines liver function to reduce the liver injuries.

Zytiga caused side effects

• Hypertension
• Diarrhea
• Vomiting
• Cough
• Hypertension
• Dyspnea
• Urinary tract infection
• Fatigue
• Joint pain, swelling or discomfort
• Hot flush
• Contusion

Lab abnormalities:

• Hypertriglyceridemia
• Lymphopenia
• Hypercholesteremia
• Hyperglycemia
• Increased AST, AST
• Hypophosphatemia
• Hypokalemia
• Anemia
• Increasing alkaline phosphatase

Post marketing reports:

• Noninfectious pneumonitis
• Myopathy, involving rhabdomyolysis
• Fulminant hepatitis, acute hepatic failure leads to death

Drug- drug interaction

Avoid the concomitant use of CYP2D6 substrate with Zytiga.

In interaction of Zytiga with pioglitazone, causes increasing the systemic exposure of pioglitazone.

Co administration of Zytiga with CYP3A4 inducers like rifampin, causes reduction in the exposure of Abiraterone.

To avoid this condition, increases the dose of Zytiga for reducing the problems.

Zytiga is an inhibitor of CYP2D6 & CYP2C8, when administering 30mg of dextromethorphan with Zytiga 100mg & 5mg of prednisolone causes increasing the AUC &C_max of dextromethorphan (CYP2D6 substrate).

Contraindications caused

Zytiga is contraindicated to pregnant & lactating women

Hypersensitivity reactions may occur due to patients is contraindicating to the component present in the Zytiga tablets.

Precautions and warning

Hypertension, hypokalemia & fluid retention:

Zytiga inhibits CYP17, causes increasing the mineralocorticoid levels leads to hypokalemia, hypertension & retention of fluids.

Concurrent use of Zytiga with corticosteroid leads to diminish adrenocorticotrophic hormone which concludes as reduction in extent & harshness of these adverse effects.

 Control the blood pressure and correct the level of potassium and fluids if required.

Adrenocortical insufficiency:

Adrenocortical deficiency occurs during the therapy of Zytiga with prednisolone.

In this condition, treatment should be interrupt or discontinue.

Monitor the signs & symptoms occurred due to this condition.

Elevation of dose of corticosteroids occurs in both before and during the treatment.

Hepatic toxicities:

In post marketing studies, due to Zytiga therapy hepatic toxicity may occur due to acute hepatic injury leads to death.

Increasing AST, bilirubin, ALT may lead to this condition.

Patients may undergo Hepatic function test frequently before or during the treatment.

Pregnancy and lactation

Pregnancy category: X

Zytiga should not be used in pregnancy condition

Breast feeding should not be allowed.

The potency of Zytiga tablets has not been evaluated in pediatric patients.

No drug safety evaluated in geriatric patients above 65 years of age.

Storage and handling

Store Zytiga tablet container should be at 20^oC to 25^oC

Protect the drug free from moisture, heat & light

Missed dose

Take the missed dose before next dose time reaches or Missed dose of Zytiga tablets should be avoided.

Consult with medical oncologist and follow the instructions

Follow the regular dosing schedule