Methylnaltrexone

Methylnaltrexone is a prescription medication used for reducing constipation caused by opioid medicine.

• Methylnaltrexone is available under the following different brand names: Relistor

Adult dosage

Injectable solution

• 8mg/0.4mL vial
• 12mg/0.6mL vial

Tablet

• 150mg

Opioid-Induced Constipation (Advanced Illness Receiving Palliative Care)

Adult dosage

• Weighing between 38-62 kg: 8 mg/dose SC every other day  
• Weighing between 62-114 kg: 12 mg/dose SC every other day
• Weighing less than 38 kg or above 114 kg: 0.15 mg/kg/dose SC every other day

Opioid-Induced Constipation (Chronic Noncancer Pain)

Adult dosage

• 12 mg SC every day, OR
• 450 mg orally every day in the morning

Dosage Considerations – Should be Given as Follows: 

• See “Dosages”

Common side effects of Methylnaltrexone include:

• stomach pain, 
• gas, 
• bloating,
• mild nausea or diarrhea,
• headache,
• muscle spasms,
• dizziness, 
• tremors, 
• feeling anxious,
• runny nose, or
• chills, sweating, or hot flashes.

Serious side effects of Methylnaltrexone include:

• hives,
• difficult breathing,
• swelling of the face, lips, tongue, or throat,
• a hole or tear in the stomach,
• severe or ongoing diarrhea,
• extreme dizziness, 
• bloody or tarry stools,
• coughing up blood or vomit that looks like coffee grounds,
• nausea or vomiting that is new or worsening symptoms, or
• symptoms of opioid medicine withdrawal--anxiety, sweating, chills, yawning, stomach pain, diarrhea.

Rare side effects of Methylnaltrexone include:

• none 

If your medical doctor is using this medicine to treat your pain, your doctor or pharmacist may already be aware of any possible drug interactions and may be monitoring you for them. Do not start, stop, or change the dosage of any medicine before checking with your doctor, health care provider, or pharmacist first

• Methylnaltrexone has no noted severe interactions with any other drugs.
• Methylnaltrexone has no noted serious interactions with any other drugs.
• Methylnaltrexone has no noted moderate interactions with any other drugs.
• Methylnaltrexone has no noted minor interactions with any other drugs.

This information does not contain all possible interactions or adverse effects. Visit the RxList Drug Interaction Checker for any drug interactions. Therefore, before using this product, tell your doctor or pharmacist of all the products you use. Keep a list of all your medications with you and share this information with your doctor and pharmacist. Check with your health care professional or doctor for additional medical advice, or if you have health questions, concerns.

Contraindications

• Documented hypersensitivity
• Known or suspected GI obstruction and patients at increased risk of recurrent obstruction

Effects of drug abuse

• None

Short-Term Effects

• See “What Are Side Effects Associated with Using Methylnaltrexone?”

Long-Term Effects

• See “What Are Side Effects Associated with Using Methylnaltrexone?”

Cautions

• Discontinue if severe/persistent diarrhea develops
• GI perforation reported with other PAMORA in patients with conditions associated with reduced structural integrity in the wall of the GI tract (eg, PUD, Ogilvie syndrome, diverticular disease, infiltrative GI malignancies, peritoneal metastases, Crohn disease); monitor for development of severe, persistent, or worsening abdominal pain; discontinue naloxegol in patients who develop these symptoms
• Symptoms consistent with opioid withdrawal (eg, hyperhidrosis, chills, diarrhea, abdominal pain, anxiety, irritability, yawning) were reported; monitoring for symptoms of withdrawal in such patients
• Therapy administration for longer than four months not studied; discontinue therapy when opioid therapy has ended
• Use with caution in hepatic or renal impairment; dosage adjustments are necessary

Pregnancy and Lactation

• The limited available data in pregnant women are not sufficient to inform a drug-associated risk for major birth defects and miscarriages; there are clinical considerations when the drug is used by pregnant women; advise pregnant women of the potential risk to a fetus
• Use during pregnancy may precipitate opioid withdrawal in a fetus due to immature fetal blood-brain barrier

Lactation

• No information regarding the presence of methylnaltrexone in human milk, effects on the breastfed infant, or milk production; methylnaltrexone is present in rat milk; because of potential for serious adverse reactions, including opioid withdrawal, in breastfed infants, advise women that breastfeeding is not recommended during treatment