Methylnaltrexone

Methylnaltrexone is a prescription medication used to treat constipation caused by prescription pain medicines called opioids (narcotics). Methylnaltrexone belongs to a group of drugs called peripherally acting mu-opioid receptor antagonists, which reverse the effects of opioids on the bowels, without affecting the pain relief from opioid treatment.

Methylnaltrexone is available in tablet form and is typically taken once a day, with water. Take Relistor tablets on an empty stomach at least 30 minutes before your first meal of the day. 

This medication also comes in an injectable form and is given just under the skin once a day in the upper arm, stomach, or thigh.

Common side effects of methylnaltrexone include stomach pain, gas, and nausea.

Methylnaltrexone is a prescription medicine used to treat constipation that is caused by prescription pain medicines, called opioids, when other medicines for constipation, called laxatives, have not worked well enough.

Methylnaltrexone tablets and injection are used to treat constipation caused by opioids in adults with long-lasting pain that is not caused by cancer.

Methylnaltrexone injection is used to treat constipation caused by opioids in adults who are receiving treatment for advanced illness, after treating constipation with other treatments that have not been successful. 

It is not known if this medication is safe and effective if used for longer than 4 months in people with advanced illness. It is also not known if this medication is safe and effective in children.

This medication may be prescribed for other uses. Ask your doctor or pharmacist for more information.

 

Take methylnaltrexone exactly as prescribed by your doctor. Follow the directions on your prescription label carefully.

The methylnaltrexone dose your doctor recommends will be based on the following:

• other medical conditions you have
• other medications you are taking
• how you respond to this medication
• your liver function
• your weight

The recommended dose of Relistor (methylnaltrexone) tablets is 450 mg once daily.

The recommended dose of Relistor (methylnaltrexone) injection is 8 mg subcutaneously for opioid-induced constipation and advanced illness adult patients weighing 38 kg to less than 62 kg or 12 mg subcutaneously for patients weighing 62 kg to 114 kg. 

Adult patients whose weight falls outside of these ranges should be dosed at 0.15 mg/kg.

Serious side effects have been reported with methylnaltrexone including the following:

• Tear in your stomach or intestinal wall. Stomach pain that is severe can be a sign of a serious medical condition. If you get stomach pain that is severe, does not go away, or gets worse, stop taking this medication and seek emergency medical attention.
• Diarrhea that is severe or that will not go away. Stop taking this medication and call your healthcare provider if you get diarrhea that is severe or that does not go away during treatment with methylnaltrexone.
• Opioid withdrawal. You may have symptoms of opioid withdrawal during treatment with methylnaltrexone including sweating, chills, diarrhea, stomach pain, anxiety, and yawning. Tell your healthcare provider if you have any of these symptoms.

Do not take methylnaltrexone if you:

• are allergic to methylnaltrexone
• have or may have a blockage in your intestines called a mechanical bowel obstruction.

Serious side effects have been reported with methylnaltrexone. See the “Methylnaltrexone Precautions” section.

Common side effects of methylnaltrexone include:

• abdominal (stomach) pain
• gas
• headache
• swelling or a feeling of fullness or pressure in your abdomen
• anxiety
• muscle spasms
• runny nose
• chills
• nausea
• dizziness
• diarrhea
• sweating
• hot flush
• tremor

If you get diarrhea that is severe or does not stop while taking methylnaltrexone, stop taking it and call your healthcare provider.

If you get stomach pain that is severe or will not go away, or nausea or vomiting that is new or worse, stop taking methylnaltrexone and call your healthcare provider.

These are not all of the possible side effects of methylnaltrexone. Tell your healthcare provider if you have any side effect that bothers you or that does not go away.

Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1‑800‑FDA‑1088.

 

Tell your doctor about all the medicines you take, including prescription and non-prescription medicines, vitamins, and herbal supplements. Especially tell your doctor if you take other opioid antagonists. This is because when taken together they increase the risk of opioid withdrawal.

This is not a complete list of methylnaltrexone drug interactions. Ask your doctor or pharmacist for more information.

Tell your doctor if you are pregnant or plan to become pregnant.

The FDA categorizes medications based on safety for use during pregnancy. Five categories - A, B, C, D, and X, are used to classify the possible risks to an unborn baby when a medication is taken during pregnancy.

Methylnaltrexone falls into category B. There are no well-done studies that have been done in humans with methylnaltrexone. But in animal studies, pregnant animals were given this medication, and the babies did not show any medical issues related to this medication.

Taking methylnaltrexone during pregnancy may cause opioid withdrawal symptoms in your unborn baby. Tell your healthcare provider right away if you become pregnant during treatment with Relistor.

It is not known if methylnaltrexone crosses into human milk. Because many medications can cross into human milk and because of the possibility for serious adverse reactions in nursing infants with use of this medication, a choice should be made whether to stop nursing or stop the use of this medication. 

Taking this medication while you are breastfeeding may cause opioid withdrawal in your baby. Do not breastfeed during treatment with methylnaltrexone.