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(naltrexone) Extended-release Injectable Suspension


VIVITROL® (naltrexone for extended-release injectable suspension) is supplied as a microsphere formulation of naltrexone for suspension, to be administered by intramuscular injection. Naltrexone is an opioid antagonist with little, if any, opioid agonist activity.

Naltrexone is designated chemically as morphinan-6-one, 17 (cyclopropylmethyl) 4,5-epoxy3,14-dihydroxy-(5α) (CAS Registry # 16590-41-3). The molecular formula is C20H23NO4 and its molecular weight is 341.41 in the anhydrous form (ie, < 1% maximum water content). The structural formula is:

VIVITROL® (naltrexone for extended-release injectable suspension) Structural Formula Illustration

Naltrexone base anhydrous is an off-white to a light tan powder with a melting point of 168170°C (334-338°F). It is insoluble in water and is soluble in ethanol.

VIVITROL is provided as a carton containing a vial each of VIVITROL microspheres and diluent, one 5-mL syringe, one 1-inch 20-gauge preparation needle, two 1 °-inch 20-gauge and two 2-inch 20-gauge administration needles with needle protection device.

VIVITROL microspheres consist of a sterile, off-white to light tan powder that is available in a dosage strength of 380 mg of naltrexone per vial. Naltrexone is incorporated in 75:25 polylactide-co-glycolide (PLG) at a concentration of 337 mg of naltrexone per gram of microspheres.

The diluent is a clear, colorless solution. The composition of the diluent includes carboxymethylcellulose sodium salt, polysorbate 20, sodium chloride, and water for injection. The microspheres must be suspended in the diluent prior to injection.

What are the possible side effects of naltrexone injection (Vivitrol)?

Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.

Call your doctor at once if you have any of these serious side effects:

  • blurred vision or eye problems;
  • fast heartbeat;
  • wheezing, difficulty breathing;
  • mood changes, hallucinations (seeing or hearing things), confusion, thoughts of hurting yourself;
  • nausea, stomach pain, low fever, loss of appetite, dark urine, clay-colored stools, jaundice (yellowing of the skin or...

Read All Potential Side Effects and See Pictures of Vivitrol »

What are the precautions when taking naltrexone xr inj (Vivitrol)?

Before using naltrexone, tell your doctor or pharmacist if you are allergic to it; or if you have any other allergies. This product may contain inactive ingredients, which can cause allergic reactions or other problems. Talk to your pharmacist for more details.

Before using this medication, tell your doctor or pharmacist your medical history, especially of: current or recent use (in the last 7 to 14 days) of any type of opioid drug (such as morphine, methadone, buprenorphine), bleeding problems (such as hemophilia, low platelets), kidney disease, liver problems.

You should carry or wear medical identification stating that you are using this drug so that appropriate treatment can be given in a medical emergency. See also Medical Alert section.

This drug may make you...

Read All Potential Precautions of Vivitrol »

Last reviewed on RxList: 12/21/2016
This monograph has been modified to include the generic and brand name in many instances.

Vivitrol - User Reviews

Vivitrol User Reviews

Now you can gain knowledge and insight about a drug treatment with Patient Discussions.

Here is a collection of user reviews for the medication Vivitrol sorted by most helpful. Patient Discussions FAQs

Report Problems to the Food and Drug Administration


You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.

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