Methylnaltrexone oral / injection

Name: Methylnaltrexone oral / injection

What should I discuss with my health care provider before using methylnaltrexone?

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:

  • cancer;

  • a stomach ulcer;

  • perforation (a hole or tear) in stomach or intestines;

  • kidney disease;

  • liver disease; or

  • colitis or other intestinal disorder such as Crohn's disease, diverticulitis, or Ogilvie's syndrome.

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.

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:

  • stomach pain, gas, bloating;

  • mild nausea or diarrhea;

  • headache, muscle spasms;

  • dizziness, tremors, feeling anxious;

  • runny nose; or

  • chills, sweating, or hot flashes.

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.

For Healthcare Professionals

Applies to methylnaltrexone: oral tablet, subcutaneous kit, subcutaneous solution


Very common (10% or more): Abdominal pain (up to 29%), flatulence (up to 13%), nausea (up to 12%)
Common (1% to 10%): Diarrhea,
Postmarketing reports: Perforation, cramping, vomiting[Ref]

Nervous system

Common (1% to 10%): Dizziness, tremor[Ref]


Common (1% to 10%): Hyperhidrosis, flushing[Ref]


Common (1% to 10%): Chills
Postmarketing reports: Malaise, pain, cases of opioid withdrawal[Ref]


In an open-label, uncontrolled study (n=1034), 4 myocardial infarctions (1 fatal), 1 stroke (fatal), 1 fatal cardiac arrest, and 1 sudden death were reported. It is not possible to establish a relationship between these events and use of this drug.[Ref]

Frequency not reported: Myocardial infarctions[Ref]


The most common adverse reactions included abdominal pain, nausea, diarrhea, hyperhidrosis, hot flush, tremor, and chills.[Ref]


Common (1% to 10%): Injection site reactions including stinging, burning, pain, redness, and edema[Ref]

Some side effects of methylnaltrexone may not be reported. Always consult your doctor or healthcare specialist for medical advice. You may also report side effects to the FDA.

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.


Safety and efficacy have not been established in patients younger than 18 years.

Consult WARNINGS section for additional precautions.

Methylnaltrexone Pregnancy Warnings

Animal studies have revealed evidence of reproductive toxicity at high doses; however no evidence of teratogenicity has been reported in rats or rabbits. Use of this drug during pregnancy may precipitate opioid withdrawal in a fetus due to the immature fetal blood brain barrier. There are no controlled data in human pregnancy. AU TGA pregnancy category B1: Drugs which have been taken by only a limited number of pregnant women and women of childbearing age, without an increase in the frequency of malformation or other direct or indirect harmful effects on the human fetus having been observed. Studies in animals have not shown evidence of an increased occurrence of fetal damage US FDA pregnancy category C: Animal reproduction studies have shown an adverse effect on the fetus and there are no adequate and well-controlled studies in humans, but potential benefits may warrant use of the drug in pregnant women despite potential risks.

This drug should be used during pregnancy only if the benefit outweighs the risk. AU TGA pregnancy category: B1 US FDA pregnancy category: C May precipitate opioid withdrawal in a fetus