Abarelix

Summary

Abarelix is a synthetic GnRH antagonist peptide approved for palliative treatment of advanced symptomatic prostate cancer. It achieved rapid testosterone suppression without the testosterone flare seen with GnRH agonists. It was withdrawn from the US market due to serious immediate-onset systemic allergic reactions and limited commercial uptake.

Mechanism of Action

Competitively blocks gonadotropin-releasing hormone (GnRH) receptors in the pituitary gland, directly suppressing LH and FSH secretion without an initial testosterone surge (flare), leading to rapid reduction in testosterone to castrate levels.

Routes of Administration

Goals & Uses

• Palliative treatment of advanced prostate cancerOncologyHigh
• Reduction of PSA levelsBiomarker ResponseHigh
• Testosterone suppression to castrate levelsHormonal TherapyHigh
• Prevention of testosterone flareOncology / Hormonal SafetyHigh

Contraindications

• Patients who can be managed with LHRH agonistsClinical SuitabilityModerate
• Female sex (women of childbearing potential)PopulationHigh
• History of serious hypersensitivity to abarelixAllergyHigh
• Pediatric usePopulationHigh
• QT prolongation / long QT syndromeCardiacHigh

Adverse Effects

• Injection site reactionsLocalCommon
• QTc prolongationCardiacUncommon
• Elevated transaminasesHepaticUncommon
• Hot flashesEndocrine / VasomotorCommon
• Immediate-onset systemic allergic reactionImmunologicUncommon
• Decreased libido / erectile dysfunctionSexual / EndocrineCommon

Drug Interactions

• QT-prolonging agents (e.g., antiarrhythmics, antipsychotics)High
• Anticoagulants (warfarin)Moderate

Population Constraints

• Pediatric patientsAgeAbsolute
• Patients with pre-existing QT prolongationCardiacRelative
• Patients with hepatic impairmentOrgan FunctionRelative
• WomenSexAbsolute

Regulatory Status

• European UnionUnknownAbarelix did not receive EMA approval; Degarelix (a related GnRH antagonist) is the approved alternative in Europe.
• United StatesWithdrawnApproved: Palliative treatment of advanced symptomatic prostate cancer in men for whom LHRH agonist therapy is not appropriate and who refuse surgical castrationFDA approved November 2003 (NDA 21-320); voluntarily withdrawn from market in 2005 by Praecis Pharmaceuticals due to serious allergic reactions and commercial viability concerns.
• United KingdomUnknownNot approved by MHRA; degarelix is the available GnRH antagonist in the UK market.

FDA approved in November 2003 (Plenaxis) for symptomatic advanced prostate cancer in patients who refuse surgical castration and are not candidates for LHRH agonists. Voluntarily withdrawn from US market by Praecis Pharmaceuticals in 2005 due to risk of serious allergic reactions and commercial reasons. Available under a restricted distribution program (REMS-like) during its market period.

Evidence & Sources

No sources recorded yet.