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Plenaxis Side Effects

Generic Name: abarelix

Note: This document contains side effect information about abarelix. Some of the dosage forms listed on this page may not apply to the brand name Plenaxis.

Applies to abarelix: intramuscular powder for injection


Endocrine side effects have included hot flushes (79%), sleep disturbance (44%), breast enlargement (30%), and breast pain/nipple tenderness (20%) as pharmacological consequences of androgen deprivation.[Ref]


General side effects including pain (31%) and fatigue (10%) have been reported.[Ref]


Musculoskeletal side effects including back pain (17%) have been reported.[Ref]


Physicians should carefully consider whether the risks of abarelix (the active ingredient contained in Plenaxis) outweigh the benefits in patients with baseline QTc values >450 msec and in patients taking class IA or class III antiarrhythmic medications.[Ref]

Cardiovascular side effects including peripheral edema (15%) and prolongation of the QT interval have been reported.[Ref]


Gastrointestinal side effects including constipation (15%), diarrhea (11%), and nausea (10%) have been reported.[Ref]

Nervous system

Nervous system side effects including dizziness (12%) and headache (12%) have been reported.[Ref]


Respiratory side effects including upper respiratory tract infection (12%) have been reported.[Ref]


Genitourinary side effects including dysuria (10%), micturition frequency (10%), urinary retention (10%), and urinary tract infection (10%) have been reported.[Ref]


Hypersensitivity side effects including immediate-onset allergic reactions (3.7%), sometimes resulting in hypotension and syncope, have been reported to have occurred after administration of abarelix (the active ingredient contained in Plenaxis) [Ref]

The allergic reaction included urticaria, pruritus, hypotension, and syncope.

Immediate-onset reactions have been reported to have occurred following any administration of abarelix, including the initial dose. The cumulative risk for such a reaction increases with the duration of treatment.

Following each injection of abarelix, patients should be observed for at least 30 minutes in the office. If an allergic reaction associated with hypotension and/or syncope does occur, supportive measures such as leg elevation, oxygen, IV fluids, antihistamines, corticosteroids, and epinephrine should be administered as needed.[Ref]


Hepatic side effects including clinically meaningful increases in serum transaminases have been reported in a small percentage of patients.[Ref]


Hematologic side effects including slight decreases in hemoglobin and mean increases in serum triglycerides of approximately 10% have been reported.[Ref]


1. "Product Information. Plenaxis (abarelix)." Praecis Pharmaceuticals Inc, Waltham, MA.

Some side effects of Plenaxis may not be reported. Always consult your doctor or healthcare specialist for medical advice. You may also report side effects to the FDA.

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