Methylnaltrexone (Relistor) | Side Effects, Dosage, Uses & More
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Generic Name:

methylnaltrexone, Injectable solution

All Brands

  • Relistor
SECTION 1 of 4

Highlights for methylnaltrexone

Injectable solution
1

Methylnaltrexone is used to treat constipation caused by the use of opioids (pain medications).

2

Methylnaltrexone is an injectable drug. It’s injected beneath your skin, most often in your upper arm, thigh, or abdomen (stomach area). Your healthcare provider will show you or your caregiver how to inject this drug.

3

Methylnaltrexone is available as the brand-name drug Relistor. It’s not available as a generic drug.

4

The more common side effects of this drug include nausea, dizziness, diarrhea, or pain in the abdomen.

5

You should stop using methylnaltrexone if you stop taking your opioid pain medication.

IMPORTANT INFORMATION

Tearing in the wall of the stomach or intestine

A tear in the wall of your stomach or intestine is called a gastrointestinal (GI) perforation. If you have problems with your GI tract, talk with your doctor about whether this drug is safe for you. If you take this drug and have unusually severe, long-lasting, or worsening pain in your abdomen (stomach area), stop using this drug and call your doctor right away.

Severe or long-lasting diarrhea

Severe diarrhea causes six or more bowel movements per day. If you have severe diarrhea that does not go away for 48 hours, stop using this drug and call your doctor right away.

Opioid withdrawal

Withdrawal occurs when you stop taking opioid medications suddenly. This drug may cause opioid withdrawal-like symptoms. These symptoms may include sweating, chills, diarrhea, stomach pain, nervousness, or yawning.

Drug features

Methylnaltrexone is a prescription drug. It comes in the form of an injectable solution. Your healthcare provider will show you or your caregiver how to inject the drug.

Methylnaltrexone is available as the brand-name drug Relistor. It’s not available as a generic drug.

Why it's used

Methylnaltrexone is used to treat constipation caused by the use of pain medications called opioids. It’s used in people who are given opioids to relieve long-term pain that’s not caused by cancer. It’s also used in people who are given opioids to relieve their pain from advanced illness that can’t be cured. This drug is used when other constipation drugs have not worked well.

How it works

Opioid pain medications cause constipation by binding to certain receptors in your gastrointestinal tract. A receptor is a part of a cell that receives a certain substance. Methylnaltrexone also binds to these receptors. This prevents the opioids from binding to them, which helps reduce constipation.

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methylnaltrexone Side Effects

Injectable solution

More Common Side Effects

The more common side effects that can occur with use of methylnaltrexone include:

  • pain in your abdomen

  • nausea

  • diarrhea

  • sweating

  • flushing

  • tremor

  • chills

  • dizziness

  • gas

If these effects are mild, they may go away within a few days or a couple of weeks. If they’re more severe or don’t go away, talk to your doctor or pharmacist.

Serious Side Effects

Call your doctor right away if you have serious side effects. Call 9-1-1 if your symptoms feel life-threatening or if you think you’re having a medical emergency. Serious side effects and their symptoms can include the following:

  • Tearing in the wall of your stomach or intestine. Symptoms can include:

    • severe, long-lasting, or worsening pain in your abdomen
    • chills
    • fever
    • nausea
    • vomiting
  • Severe diarrhea. Symptoms can include:

    • having more than six bowel movements per day
    • diarrhea that lasts longer than 48 hours
  • Opioid withdrawal. Symptoms can include:

    • sweating
    • chills
    • diarrhea
    • pain in your abdomen
    • anxiety
    • yawning
Pharmacist's Advice
Healthline Pharmacist Editorial Team

This drug doesn’t cause drowsiness.

Disclaimer: Our goal is to provide you with the most relevant and current information. However, because drugs affect each person differently, we cannot guarantee that this information includes all possible side effects. This information is not a substitute for medical advice. Always discuss possible side effects with a healthcare provider who knows your medical history.
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methylnaltrexone May Interact with Other Medications

Injectable solution

Methylnaltrexone can interact with other medications, vitamins, or herbs you may be taking. An interaction is when a substance changes the way a drug works. This can be harmful or prevent the drug from working well.

To help avoid interactions, your doctor should manage all of your medications carefully. Be sure to tell your doctor about all medications, vitamins, or herbs you’re taking. To find out how this drug might interact with something else you’re taking, talk to your doctor or pharmacist.

Medications that might interact with this drug

Drugs you should not use with methylnaltrexone

Do not take these drugs with methylnaltrexone. Doing so can cause dangerous effects in the body. Examples of these drugs include:

  • Opioid antagonists, such as naltrexone, naloxone, buprenorphine, or buprenorphine/naloxone
    • Taking these drugs with methylnaltrexone raises your risk of symptoms of opioid withdrawal. These symptoms include sweating, chills, diarrhea, or pain in your abdomen.

Disclaimer: Our goal is to provide you with the most relevant and current information. However, because drugs interact differently in each person, we cannot guarantee that this information includes all possible interactions. This information is not a substitute for medical advice. Always speak with your healthcare provider about possible interactions with all prescription drugs, vitamins, herbs and supplements, and over-the-counter drugs that you are taking.
Drug warnings
current or past bowel blockage
People with current or past bowel blockage

If you have bowel blockage (intestinal obstruction) or have had it in the past, this drug raises your risk of tearing the wall of your stomach or intestine. The tear may cause bowel blockage to occur again.

kidney disease
People with kidney disease

Your body processes this drug more slowly if you have serious kidney disease. Your doctor will likely prescribe you half of the recommended dose. Be sure to use the pre-filled syringe. It will help you make sure your dose is correct.

Pregnant women
Pregnant women

This drug is a category C pregnancy drug. That means two things:

  1. Research in animals has shown adverse effects to the fetus when the mother takes the drug.
  2. There haven’t been enough studies done in humans to be certain how the drug might affect the fetus.

Talk to your doctor if you’re pregnant or planning to become pregnant. This drug should only be used if the potential benefit justifies the potential risk to the unborn baby. 

Using this drug while pregnant could cause opioid withdrawal in your baby. If this occurs, your baby’s symptoms could appear as soon as one day after birth and last up to six months. Your doctor might treat your baby to reduce your baby’s withdrawal symptoms.

breast-feeding
Women who are breast-feeding

It’s not known whether this drug passes into human breast milk. If it does, it could cause serious side effects in a child who is breastfed. These side effects include opioid withdrawal. 

To avoid these side effects, you should either stop breastfeeding or stop taking this drug. Talk with your doctor about which option is best for you.

seniors
For seniors

The kidneys of older adults may not work as well as they used to. This can cause your body to process drugs more slowly. As a result, more of a drug stays in your body for a longer time. This raises your risk of side effects.

children
For children

This drug has not been studied in children. It should not be used in people younger than 18 years.

call the doctor
When to call the doctor

Call your doctor right away if you become pregnant while taking this drug.

Allergies
Allergies

This drug can cause a severe allergic reaction. Symptoms can include: 

  • trouble breathing
  • swelling of your throat or tongue 

If you have an allergic reaction, call your doctor or local poison control center right away. If your symptoms are severe, call 9-1-1 or go to the nearest emergency room.

Taking this drug again if you’ve ever had an allergic reaction to it could be fatal (cause death). Be sure to tell your doctor if you’ve ever had an allergic reaction to this drug.

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How to Take methylnaltrexone (Dosage)

Injectable solution

All possible dosages and drug forms may not be included here. Your dosage, drug form, and how often you take the drug will depend on:

  • your age
  • the condition being treated
  • how severe your condition is
  • other medical conditions you have
  • how you react to the first dose

What are you taking this medication for?

Opioid-induced constipation

Brand: Relistor

Form: Single-use vial
Strengths: 12 mg/0.6 mL solution
Form: Single-use pre-filled syringe
Strengths:
  • 8 mg/0.4 mL solution
  • 12 mg/0.6 mL solution
Adult dosage (ages 18–64 years)
  • Typical dosage for people taking opioids for long-term noncancer pain: 12 mg injected under your skin once daily
  • Typical dosage for people with advanced illness that can’t be cured, who are given opioids to relieve pain: This drug should be given every other day as needed. Dosage is based on your weight. No more than one dose should be given in a 24-hour period.
  • Before starting methylnaltrexone, you should stop any other medications you take that treat constipation.
Child dosage (ages 0–17 years)

This drug has not been studied in children. It should not be used in people younger than 18 years.

Senior dosage (ages 65 years and older)

The kidneys of older adults may not work as well as they used to. This can cause your body to process drugs more slowly. As a result, more of a drug stays in your body for a longer time. This raises your risk of side effects.

Your doctor may start you on a lowered dose or a different dosing schedule. This can help keep levels of this drug from building up too much in your body.

Special considerations

Kidney problems: If you have severe kidney problems, your doctor will likely start your dose at half the normal dose.

Disclaimer: Our goal is to provide you with the most relevant and current information. However, because drugs affect each person differently, we cannot guarantee that this list includes all possible dosages. This information is not a substitute for medical advice. Always to speak with your doctor or pharmacist about dosages that are right for you.
Pharmacist's Advice
Healthline Pharmacist Editorial Team

This drug comes with serious risks if you don’t take it as prescribed.

If you stop taking the drug suddenly or don’t take it at all

Your constipation may not improve and may get worse.

If you miss doses or don’t take the drug on schedule

This drug may not work as well or may stop working completely.

If you take too much

If you’re taking opioid medication and use too much this drug, you may have opioid withdrawal. Symptoms can include:

  • chills
  • runny nose
  • sweating
  • less control of your pain

If you think you’ve taken too much of this drug, call your doctor or local poison control center. If your symptoms are severe, call 9-1-1 or go to the nearest emergency room right away.

What to do if you miss a dose

Take your dose as soon as you remember. But if you remember just a few hours before your next scheduled dose, take only one dose. Never try to catch up by taking two doses at once. This could result in dangerous side effects.

How to tell if the drug is working

Your constipation should get better.

This drug is used for long-term treatment in patients with long-term pain that’s not caused by cancer.

 

This drug is used for short-term treatment in patients with advanced illness who are receiving palliative care.

Important considerations for taking this drug
timing
Take this drug at the time(s) recommended by your doctor
storage
Store this drug carefully
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medication is refillable
A prescription for this medication is refillable
See Details
Travel
Travel
See Details
Self-management
Self-management
See Details
not usually stocked
Not every pharmacy stocks this drug. When filling your prescription, be sure to call ahead
Hidden costs
Hidden costs
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prior authorization
Insurance
See Details

Store this drug carefully

  • Store this drug at room temperature between 59°F and 86°F (15°C and 30°C).
  • Keep this medication away from light.

A prescription for this medication is refillable

You should not need a new prescription for this medication to be refilled. Your doctor will write the number of refills authorized on your prescription.

Travel

When traveling with your medication:

  • Always carry your medication with you. When flying, never put it into a checked bag. Keep it in your carry-on bag.
  • Don’t worry about airport x-ray machines. They can’t hurt your medication.
  • You may need to show airport staff the pharmacy label for your medication. Always carry the original prescription-labeled box with you.
  • Don’t put this medication in your car’s glove compartment or leave it in the car. Be sure to avoid doing this when the weather is very hot or very cold.

Self-management

This medication is a laxative. Be sure you’re near a restroom when you inject this medication. You may have a sudden urge to go to the bathroom.

Hidden costs

You’ll likely need to buy the following items to inject this medication:

  • alcohol swabs
  • cotton balls or gauze
  • adhesive bandages
  • a sharps container to safely dispose of the needles and syringes

Some vials don’t come with a needle and syringe. If you only receive the vial with your prescription, you will also need a 27-gauge, ½-inch needle and a 1-mL syringe. 

Your doctor or pharmacist can tell you where to buy all of these items. The cost will depend on where you purchase them.

Insurance

Many insurance companies require a prior authorization for this drug. This means your doctor may need to get approval from your insurance company before your insurance company will pay for the prescription.

Are there any alternatives?

There are other drugs available to treat your condition. Some may be better suited for you than others. Talk to your doctor about other drug options that may work for you.


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Content developed in collaboration with University of Illinois-Chicago, Drug Information Group

Medically reviewed by Creighton University, Center for Drug Information and Evidence-Based Practice on January 20, 2016

Disclaimer: Healthline has made every effort to make certain that all information is factually correct, comprehensive, and up-to-date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or other healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.
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