Plenaxis (Abarelix) Drug Information: Description, User Reviews, Drug Side Effects, Interactions

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February 7, 2012

Plenaxis

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The prostate gland is an organ that is located at the base or outlet (neck) of the urinary bladder. (See the diagram that follows.) The gland surrounds the first part of the urethra. The urethra is the passage through which urine drains from the bladder to exit from the penis. One function of the prostate gland is to help control urination by pressing directly against the part of the urethra that it surrounds. The main function of the prostate gland is to produce some of the substances that are found in normal semen, such as minerals and sugar. Semen is the fluid that transports the sperm to assist with reproduction. A man can manage quite well, however, without his prostate gland. (See the section on surgical treatment for prostate cancer.)

In a young man, the normal prostate gland is the size of a walnut (<30g). During normal aging, however, the gland usually grows larger. This hormone-related enlargement with aging is called b...

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Plenaxis

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Please Note: This Brand Name drug is no longer available in the US.
(Generic versions may still be available.)

Plenaxis™
(abarelix) for Injectable Suspension

WARNING

Immediate-onset systemic allergic reactions, some resulting in hypotension and syncope, have occurred after administration of Plenaxis™ . These immediate-onset reactions have been reported to occur following any administration of Plenaxis™ , including after the initial dose. The cumulative risk of such a reaction increases with the duration of treatment (see WARNINGS). Following each injection of Plenaxis™ , patients should be observed for at least 30 minutes in the office and in the event of an allergic reaction, managed appropriately.

Only physicians who have enrolled in the Plenaxis™ PLUS Program (Plenaxis™ User Safety Program), based on their attestation of qualifications and acceptance of prescribing responsibilities, may prescribe Plenaxis™ (See DOSAGE AND ADMINISTRATION and HOW SUPPLIED).
Plenaxis™ is indicated for the palliative treatment of men with advanced symptomatic prostate cancer, in whom LHRH agonist therapy is not appropriate and who refuse surgical castration, and have one or more of the following: (1) risk of neurological compromise due to metastases, (2) ureteral or bladder outlet obstruction due to local encroachment or metastatic disease, or (3) severe bone pain from skeletal metastases persisting on narcotic analgesia.
The effectiveness of Plenaxis™ in suppressing serum testosterone to castrate levels decreases with continued dosing in some patients (see CLINICAL PHARMACOLOGY, Pharmacodynamics). Effectiveness beyond 12 months has not been established. Treatment failure can be detected by measuring serum total testosterone concentrations just prior to administration on Day 29 and every 8 weeks thereafter (see WARNINGS).

DRUG DESCRIPTION

Abarelix for injectable suspension (Plenaxis™ ) is a synthetic decapeptide with potent antagonistic activity against naturally occurring gonadotropin releasing-hormone (GnRH). Plenaxis™ inhibits gonadotropin and related androgen production by directly and competitively blocking GnRH receptors in the pituitary.

Abarelix is chemically described as acetyl-D-β-naphthylalanyl-D-4-chlorophenylalanyl- D-3-pyridylalanyl-L-seryl-L-N-methyl-tyrosyl-D-asparagyl-L-leucyl-L-N(ε)-isopropyllysyl- L-prolyl-D-alanyl-amide. It is initially manufactured as an acetate water complex and converted to a carboxymethylcellulose (CMC) water complex in manufacturing the drug product. The molecular weight for abarelix anhydrous free base is 1416.06.

The structural formula for abarelix peptide is:

Plenaxis™ (abarelix) Structural Formula Illustration

Abarelix for injectable suspension is supplied as a white to off-white sterile dry powder which, when mixed with the diluent, 0.9% Sodium Chloride Injection, USP, becomes a depot suspension intended for intramuscular (IM) injection. The single-dose vial contains 113 mg of anhydrous free base abarelix peptide (net) supplied in an abarelix CMC complex. This complex also contains 19.1 to 31 mg of CMC. After the vial is reconstituted with 2.2 mL of 0.9% sodium chloride injection, 2 mL is administered to deliver a dose of 100 mg of abarelix (net) as the abarelix CMC complex at a pH of 5±1.

What are the possible side effects of abarelix (Plenaxis)?

In some cases, the use of abarelix has resulted in serious allergic reactions. An allergic reaction may occur after any injection of the medication, including, but not limited to the first dose. Patients should be observed in the doctor's office for at least 30 minutes following each dose so that immediate treatment of an allergic reaction can be obtained if needed.

Other, less serious side effects may be more likely to occur. Talk to your doctor if you experience