(a-ba-re-lix) ,


(trade name)


Therapeutic: antineoplastics
Pharmacologic: gnrh antagonist
Pregnancy Category: X


Advanced prostate cancer when LHRH agonists are inappropriate or surgical castration is refused and there is risk of neurologic compromise from metastatic disease, ureteral/bladder obstruction due to local/metastatic disease or severe metastatic bone pain unresponsive to adequate opioid analgesia.


Directly and competitively blocks pituitary GnRH receptors, thereby suppressing production of luteinizing hormone (LH) and follicle-stimulating hormone (FSH). This results in decreased production of testosterone by the testes, which is not accompanied by an initial increase in testosterone.

Therapeutic effects

Suppressed spread of metastatic prostate cancer, with decreased neurologic complications, bladder outlet obstruction and need for opioid analgesics.


Absorption: Well absorbed following IM administration.
Distribution: Extensively distributed.
Protein Binding: 96–99%.
Metabolism and Excretion: Metabolized by hydrolysis of peptide bonds; 13% excreted unchanged in urine.
Half-life: 13.2 days.

Time/action profile (decrease in testosterone levels)

IM2 days3 days (blood level)1 mo*
*Testosterone levels at mo reflect medical castration


Contraindicated in: Hypersensitivity; Adult females or children.
Use Cautiously in: Patients with pre-existing QTc prolongation or concurrent use of Class IA antiarrhythmics (amiodarone, sotalol); Weight >225 pounds (decreased effectiveness over time).

Adverse Reactions/Side Effects

Central nervous system

  • dizziness (most frequent)
  • fatigue (most frequent)
  • headache (most frequent)
  • sleep disturbances (most frequent)


  • peripheral edema (most frequent)
  • prolonged QTc interval


  • constipation (most frequent)
  • diarrhea (most frequent)
  • nausea (most frequent)
  • increased transaminases


  • dysuria (most frequent)
  • urinary frequency (most frequent)


  • hot flushes (most frequent)


  • breast enlargement/nipple tenderness (most frequent)


  • back pain (most frequent)


  • allergic reactions
  • decreased bone mineral density


Drug-Drug interaction

None noted.


Intramuscular (Adults) 100 mg on Day 1, 15, and 29 and then every 4 wk thereafter.


Sterile powder for suspension (requires reconstitution): 113 mg/vial (yields 100 mg/2 mL dose)

Nursing implications

Nursing assessment

  • Observe patient for at least 30 min following injection for immediate-onset systemic allergic reactions (urticaria, pruritus, hypotension, syncope). Treat symptomatically; if hypotension or syncope occur measures such as leg elevation, oxygen, IV fluids, antihistamines, corticosteroids, and epinephrine should be used. Risk of reaction increases with duration of treatment.
  • Lab Test Considerations: Measure serum total testosterone concentrations just prior to administration on Day 29 and every 8 wk thereafter. Overall effectiveness may decrease with increased duration of therapy.
    • May cause ↑ serum AST and ALT levels. Monitor serum transaminase levels prior to and periodically during therapy.
    • Monitor serum PSA levels periodically during therapy.
    • May cause slight ↓ in hemoglobin.
    • May cause ↑ in serum triglycerides.
    • May cause ↓ in bone mineral density.

Potential Nursing Diagnoses

Chronic pain (Side Effects)


  • Abarelix should be prescribed only by physicians enrolled and qualified by the Plenaxis User Safety Program.
  • Intramuscular: Prior to reconstitution, shake vial. Hold vial at 45° angle and tap lightly on table to break up any caking. Using enclosed 18 gauge needle and 3 cc syringe, withdraw 2.2 mL of 0.9% NaCl. Discard remaining diluent. With vial upright, insert needle all the way into vial and inject diluent quickly. Before withdrawing needle, remove 2.2 mL of air. Shake vial immediately for approximately 15 seconds. Allow vial to stand for approximately 2 min. Tap vial to reduce foaming and swirl vial occasionally. Do not reinject air into vial. Locate a second injection spot on stopper and insert the 18 gauge needle. Invert vial and draw up some of the suspension into syringe and reinject into remaining solids in vial without removing needle. Repeat until all solids are dispersed. Swirl vial before withdrawal and withdraw entire contents (at least 2 mL) by positioning needle in vial at a 45° angle. Pull the plunger back to recover residual suspension in needle, then exchange needle with the enclosed 22 gauge 1 1/2 inch injection needle. Administer the entire reconstituted suspension IM immediately. Must be administered within 1 hr of reconstitution.

Patient/Family Teaching

  • Inform patient of purpose and risks of abarelix.
  • May cause dizziness. Caution patient to avoid driving and other activities requiring alertness until response to medication is known.
  • Advise patient to notify physician immediately if symptoms of immediate-onset systemic allergic reaction occur.

Evaluation/Desired Outcomes

  • Decreased serum testosterone levels resulting in suppressed spread of metastatic prostate cancer, with decreased neurologic complications, bladder outlet obstruction and need for opioid analgesics.
Drug Guide, © 2015 Farlex and Partners
References in periodicals archive ?
The company has won several clinical and commercial contracts in the past several months, including the supply agreement for Plenaxis, a highly potent GnRH blocker for prostate cancer.
The company has won around pounds 1.2m of new business in the last few months, including the commercial supply of licensed cancer product Plenaxis' for Specialty European Pharma.
Some examples of the 25 designated medications are alosetron (Lotronex), which is used to treat irritable bowel syndrome but can cause serious gastrointestinal side effects; ambrisentan (Letairis), which is used to treat pulmonary arterial hypertension but can cause liver damage and birth defects; and abarelix (Plenaxis), which is used to treat prostate cancer but can cause a serious allergic reaction.
In May, IURTC leaders honored Roger Roeske, professor in the Department of Biochemistry and Molecular Biology at the IU School of Medicine in Indianapolis, for research that led to Plenaxis, a drug therapy for prostate cancer patients.
He also notes that last month the Federal Drug Administration approved Cialis, the Lilly/Icos pill for erectile dysfunction, and Praecis' prostate cancer drug Plenaxis, and he cites a Standard & Poor's report predicting that biotech industry sales are set to grow more than 20% in 2004.
Results from the clinical trial supporting this indication were presented at the 2001 Annual Meeting of the American Society of Clinical Oncology, and suggest that patients, when placed on Plenaxis therapy, were able to avoid surgical castration (orchiectomy), the study's primary clinical goal (endpoint).
In summary, we are currently conducting a pharmacokinetic study of Plenaxis for the treatment of endometriosis.
Amgen also announced that it is ending a pact with Praecis Pharmaceuticals Inc., another biotechnology firm, to develop and commercialize Plenaxis (a drug to treat hormonally responsive prostate cancer and endometriosis) and has suspended talks with Guilford Pharmaceuticals Inc.