DrugindexOnline^{2nd edition}

Pronouncation: (ab-ah-RELL-ix)
Class: Gonadotropin-releasing hormone antagonist

Trade Names:
Plenaxis
- Injectable Suspension 113 mg

Mechanism of Action

Pharmacology

Directly suppresses luteinizing hormone and follicle stimulating hormone secretion, thereby reducing the secretion of testosterone by the testes.

Pharmacokinetics

Absorption

Slowly absorbed following IM injection, reaching a peak concentration of 43.4 ng/mL approximately 3 days after injection.

Distribution

Vd is about 4,040 L. AUC is about 500 ng•day/mL; 96% to 99% is protein bound.

Metabolism

Major metabolites are formed via hydrolysis of peptide bonds.

Elimination

Approximately 13% unchanged in the urine. The t _½ is about 13.2 days.

Indications and Usage

Palliative treatment of advanced symptomatic prostate cancer in men in whom luteinizing hormone-releasing hormone agonist therapy is not appropriate and who refuse surgical castration, and have 1 or more of the following: risk of neurological compromise caused by metastases; ureteral or bladder outlet obstruction caused by local encroachment or metastatic disease; or severe bone pain from skeletal metastases persisting on narcotic analgesia.

Contraindications

Women; pediatric patients; pregnancy; hypersensitivity to any component of the product.

Dosage and Administration

Adults

IM 100 mg to buttock on days 1, 15, 29 (week 4) and every 4 wk thereafter.

General Advice

• Reconstitute powder following manufacturer's guidelines.
• Do not administer if particulate matter, cloudiness, or discoloration noted.
• Administer solution by IM injection into buttock within 1 h of reconstitution.
• Discard any unused solution. Do not save for future use.

Storage/Stability

Store vials at controlled room temperature (59° to 86°F).

Drug Interactions

Class IA (eg, quinidine, procainamide), class III (eg, amiodarone, sotalol) antiarrhythmic agents

Because the QT interval may be prolonged by abarelix, benefits of use should outweigh risk of potential QT prolongation.

Laboratory Test Interactions

None well documented.

Adverse Reactions

CNS

Sleep disturbances (44%); dizziness, headache (12%); fatigue (10%).

GI

Constipation (15%); diarrhea (11%); nausea (10%).

Genitourinary

Breast enlargement (30%); breast pain/nipple tenderness (20%); dysuria, micturition frequency, urinary retention, UTI (10%).

Lab Tests

Increased serum triglycerides (10%); increased ALT (8%); increased AST (3%).

Respiratory

Upper respiratory tract infection (12%).

Miscellaneous

Hot flushes (79%); pain (31%); back pain (17%); peripheral edema (15%); immediate-onset systemic allergic reactions.

Precautions

Warnings Immediate-onset systemic allergic reactions, some resulting in hypotension and syncope, can occur. May only be prescribed by physicians who have enrolled in the Plenaxis PLUS program.

Monitor Allergic reaction Monitor patient for immediate-onset allergic reaction (eg, hives, itching, hypotension, syncope) for at least 30 min following each injection. Immediately inform health care provider if noted and be prepared to treat appropriately. Treatment assessment Periodically assess and document response to treatment. Inform health care provider if any of the symptoms of advanced prostate cancer (eg, bone pain, neurological compromise, urinary symptoms) are not improving or are worsening.

Pregnancy

Category X .

Lactation

Undetermined.

Children

Safety and efficacy not established.

Effectiveness

A decrease in overall effectiveness with increased duration of treatment may occur, especially in patients weighing more than 225 pounds.

Prolongation of QT interval

May occur.

Patient Information

• Advise patient that medication is not a cure for prostate cancer but is being used to provide relief of symptoms caused by the prostate cancer.
• Review dosing schedule with patient (injections on days 1, 15, and 29 then every 4 wk thereafter).
• Advise patient that medication will be prepared and administered by a health care professional in a medical setting.
• Advise patient that allergic reactions can occur following the injection and to remain in the medical setting for at least 30 min following each injection so that a reaction can be treated if it occurs.
• Advise patient that hot flushes and sleep disturbances are the most common adverse reactions and to inform health care provider if they occur and are intolerable or if any other adverse reaction becomes bothersome.
• Advise patient that drug may cause dizziness and to use caution while driving or performing other tasks requiring mental alertness until tolerance is determined.