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Methylnaltrexone (oral/injection)

Generic Name: methylnaltrexone (oral/injection) (METh IL nal TREX own)
Brand Name: Relistor

Medically reviewed by on Jul 9, 2020 – Written by Cerner Multum

What is methylnaltrexone?

Methylnaltrexone blocks the effects of opioid medication. An opioid is sometimes called a narcotic.

Methylnaltrexone reduces constipation caused by using narcotic medicine for 4 weeks or longer. Methylnaltrexone works by preventing constipation without reducing the pain-relieving effects of the narcotic.

Methylnaltrexone is given to adults who use narcotic medicine to treat severe chronic pain that is not caused by cancer. Methylnaltrexone injection is also for use in adults who have advanced illness and are receiving palliative care (treatment to relieve suffering and improve quality of life during a serious illness).

Methylnaltrexone is usually given after laxatives have been tried without successful treatment of constipation.

Methylnaltrexone may also be used for purposes not listed in this medication guide.

Important Information

You should not use methylnaltrexone if you have a blockage in your stomach or intestines.

Before taking this medicine

You should not use methylnaltrexone if you are allergic to it, or if you have:

  • a blockage in your stomach or intestines.

To make sure methylnaltrexone is safe for you, tell your doctor if you have ever had:

It is not known whether this medicine will harm an unborn baby. If you use methylnaltrexone while you are pregnant, your baby could become dependent on the drug. This can cause life-threatening withdrawal symptoms in the baby after it is born. Babies born dependent on habit-forming medicine may need medical treatment for several weeks. Tell your doctor if you are pregnant or plan to become pregnant.

It is not known whether methylnaltrexone passes into breast milk or if it could harm a nursing baby. You should not breast-feed while using this medicine.

Methylnaltrexone is not approved for use by anyone younger than 18 years old.

How should I use methylnaltrexone?

Follow all directions on your prescription label. Do not use methylnaltrexone in larger or smaller amounts or for longer than recommended.

This medicine is given daily or every other day. Do not use methylnaltrexone more often than once every 24 hours.

Methylnaltrexone can produce a bowel movement within 30 minutes. Be sure you are near a restroom when you use this medicine.

Take methylnaltrexone tablets on an empty stomach, at least 30 minutes before your first meal of the day.

Take the tablets with a full glass of water.

Methylnaltrexone injection is injected under the skin. You may be shown how to use injections at home. Do not give yourself this medicine if you do not understand how to use the injection and properly dispose of used needles and syringes. Your care provider will show you the best places on your body to inject methylnaltrexone. Use a different place each time you give an injection. Do not inject into the same place two times in a row.

Prepare your dose only when you are ready to give an injection. After loading a syringe, keep it at room temperature protected from light and use it within 24 hours. Methylnaltrexone injection should look clear or slightly yellow in color. Do not use the medication if it has changed colors or has particles in it. Call your pharmacist for new medicine.

Tell your doctor if you have any changes in weight. Methylnaltrexone injection doses are based on weight, and any changes may affect the dose.

Each single use vial (bottle) of methylnaltrexone injection is for one use only. Throw away after one use, even if there is still some medicine left in it after injecting your dose.

Use a disposable needle and syringe only once. Follow any state or local laws about throwing away used needles and syringes. Use a puncture-proof "sharps" disposal container (ask your pharmacist where to get one and how to throw it away). Keep this container out of the reach of children and pets.

Call your doctor if your symptoms do not improve after 3 days of treatment with methylnaltrexone tablets or injection.

After you stop using your pain medication, you should also stop using methylnaltrexone.

Store at room temperature away from moisture, heat, and light. Do not freeze the vials or prefilled syringes. Keep the tablets in their original container, along with the 2 canisters of moisture-absorbing preservative.

Read all patient information, medication guides, and instruction sheets provided to you. Ask your doctor or pharmacist if you have any questions.

What happens if I miss a dose?

Use the missed dose as soon as you remember. Skip the missed dose if it is almost time for your next scheduled dose. Do not use extra medicine to make up the missed dose.

Do not use this medicine more than once in a 24-hour period.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

When you have an opioid medication in your system, an overdose of methylnaltrexone could stimulate opioid withdrawal symptoms. Common withdrawal symptoms are yawning, irritability, sweating, chills, vomiting, diarrhea, and body aches.

What should I avoid while using methylnaltrexone?

Do not use any other laxatives that your doctor has not prescribed.

Methylnaltrexone side effects

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

Stop using methylnaltrexone and call your doctor at once if you have:

  • severe stomach pain that gets worse or will not go away;

  • severe or ongoing diarrhea;

  • extreme dizziness, or feeling like you might pass out;

  • bloody or tarry stools, coughing up blood or vomit that looks like coffee grounds;

  • nausea or vomiting that are new or worsening symptoms; or

  • symptoms of narcotic medicine withdrawal--anxiety, sweating, chills, yawning, stomach pain, diarrhea.

Common side effects may include:

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Methylnaltrexone dosing information

Usual Adult Dose for Constipation - Drug Induced:

Opioid-Induced Constipation in Patients with Chronic Non-Cancer Pain:
-Oral: 450 mg orally once a day in the morning
-Parenteral: 12 mg subcutaneously once a day

-Prior to initiation, discontinue all maintenance laxative therapy; laxatives can be used as needed for suboptimal response after 3 days.
-Patients should be within close proximity to a bathroom once this drug is administered.
-Re-evaluate continued need for this drug when the opioid regimen is changed to avoid adverse reactions.

Opioid-Induced Constipation in Patients with Advanced Illness:
Parenteral: Weight-based dosing: Administer subcutaneously every other day as needed, but no more frequently than 1 dose in a 24-hour period:
Less than 38 kg: 0.15 mg/kg
38 kg to less than 62 kg: 8 mg (0.4 mL)
62 kg to 114 kg: 12 mg subcutaneously (0.6 mL)
More than 114 kg: 0.15 mg/kg subcutaneously

Comments: To determine injection volume for patients whose weight is less than 38 kg or more than 114 kg: multiply patient weight (kg) by 0.0075 and round up to the nearest 0.1 mL

-For the treatment of opioid-induced constipation in adult patients with chronic non-cancer pain or advanced illness who are receiving palliative care, when the response to laxative therapy has not been sufficient.

What other drugs will affect methylnaltrexone?

Other drugs may interact with methylnaltrexone, including prescription and over-the-counter medicines, vitamins, and herbal products. Tell your doctor about all your current medicines and any medicine you start or stop using.

Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.