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Medical Areas: Oncology | Family Medicine | Urology
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Plenaxis (abarelix for injectable suspension)
The following drug information is obtained from various newswires, published
medical journal articles, and medical conference presentations.
Company: Praecis Pharmaceuticals
Approval Status: Approved December 2003
Treatment Area: Prostate Cancer
Plenaxis (abarelix for injectable suspension), a
gonadotropin-releasing hormone (GnRH) antagonist, lowers the male
hormone testosterone in the blood stream. Testosterone makes some
prostate cancers grow.
Plenaxis is approved for the treatment of advanced symptomatic
prostate cancer, where LHRH agonist therapy is not appropriate and
subjects 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 (3) Severe bone pain from skeletal metastases
persisting on narcotic analgesia.
A single-dose vial contains 113 mg of abarelix peptide in powder
form, which must be mixed with .9% sodium chloride and injected
intramuscularly. Plenaxis injections are taken every two weeks for
the first month, and then every four weeks.
FDA approval of Plenaxis was based on one pivotal study
enrolling 81 subjects with advanced symptomatic at risk for flare
up if treated with LHRH agonists. The open-label, multicenter,
uncontrolled, single-arm study was designed to see if patients
could avoid orchiectomy through at least 12 weeks of treatment.
Treatment was given for at least 6 months with the option to
continue treatment in an extension trial. A dose of 100 mg of
Plenaxis was administered via IM injection on Days 1, 15 and 29,
then every 4 weeks.
Results showed that 10 of 13 subjects with bladder outlet
obstruction and a bladder drainage catheter had had the catheter
removed by 12 weeks of treatment. No subjects with vertebral or
epidural metastases and without neurological symptoms developed
neurological symptoms. In addition, 11 of 15 subjects with pain due
to skeletal metastases were able to reduce the potency, dose and/or
frequency of narcotic analgesia at 12 weeks. Medical castration,
defined as serum total testosterone concentration =50 ng/dL),was
achieved in 57 of the 72 patients (79%) by Day 8, and by 68 of 71
patients (96%) by Week 4.
Adverse events associated with the use of Plenaxis may include
(but are not limited to) the following:
- Hot flushes
- Sleep Disturbance
- Breast Enlargement
Mechanism of Action
Abarelix inhibits gonadotropin and related androgen production
by directly and competitively blocking GnRH receptors in the
pituitary gland. The drug directly suppresses luteinizing hormone
(LH) and follicle stimulating hormone (FSH) secretion and thereby
reducing the secretion of testosterone by the testes.
Crook JM, Szumacher E, Malone S, et al.
Intermittent androgen suppression in the management of prostate
cancer. Urology 1999;53:530-534.
Garnick MB, Gittelman M, Steidle C et al.
Abarelix (PPI-149), a novel and potent GnRH antagonist, induces a
rapid and profound prostate gland volume reduction (PGVR) and
androgen suppression before brachytherapy (BT) or radiation therapy
(XRT). J Urol 1998;159:220a.
Thompson IM, Zeidman EJ, Rodriguez FR. Sudden
death due to disease flare with luteinizing hormone-releasing
hormone agonist therapy for carcinoma of the prostate. J
Trachtenberg J, Gittelman M, Steidle C, Barzell W,
Friedel W, Pessis D, Fotheringham N, Campion M, Garnick
MB. Abarelix-Depot versus Leuprolide Acetate plus
bicalutamide for prostate cancer: results of multi-institutional,
randomized, phase III study in 255 patients. Proc Am Soc Clin