Methylnaltrexone Bromide

Name: Methylnaltrexone Bromide

Uses for Methylnaltrexone Bromide

Opiate-induced Constipation

Treatment of opiate-induced constipation in patients with advanced illness who are receiving palliative care and have had an insufficient response to laxative therapy.1 2

Methylnaltrexone Bromide Dosage and Administration


Sub-Q Administration

Administer by sub-Q injection into the upper arm, abdomen, or thigh.1 Use abdomen or thigh for self-administration; may use upper arm if not self-administered.1

Rotate injection sites.1 Do not inject into areas where skin is bruised, tender, red, hard, or where scars or stretch marks are present.1


Available as methylnaltrexone bromide; dosage expressed in terms of the salt.1


Opiate-induced Constipation Sub-Q

Base dosage on patient’s weight (see Table 1).1 Give one dose every other day as needed.1 Do not exceed one dose per 24-hour period.1

Determine injection volume by multiplying the patient’s weight in kg by 0.0075 (or in pounds by 0.0034) and rounding up to nearest 0.1 mL.1

Table 1. Methylnaltrexone Injection Volume and Dosage

Patient Weight (kg)

Injection Volume



See below

0.15 mg/kg1 2

38 to <62

0.4 mL

8 mg1 2

62 to 114

0.6 mL

12 mg1 2


See below

0.15 mg/kg1 2

Prescribing Limits


Opiate-induced Constipation Sub-Q

Maximum one dose per 24-hour period.1 2 Use beyond 4 months not studied.1

Special Populations

Hepatic Impairment

No dosage adjustment required in mild or moderate hepatic impairment; not studied in patients with severe hepatic impairment.1 10

Renal Impairment

Mild or moderate renal impairment: Dosage adjustment not required.1

Severe renal impairment (<30 mL/minute): Decrease dosage by 50%.1 2 (See Special Populations under Pharmacokinetics.)

End-stage renal disease requiring dialysis: Not studied.1 10

Geriatric Patients

No dosage adjustment required.1

Interactions for Methylnaltrexone Bromide

Weak inhibitor of CYP2D6 in vitro;1 2 13 no substantial inhibitory effect on CYP isoenzymes 1A2, 2A6, 2C9, 2C19, or 3A4.1

Renally Excreted Drugs

Potential for interactions with drugs eliminated by active renal tubular secretion not studied.1

Specific Drugs




No substantial effect on metabolism of dextromethorphan1 2 13


  • Peripherally acting μ-opiate receptor antagonist;1 7 8 9 12 13 quaternary amine derivative of naltrexone.4 7 9 11 13

  • Blocks μ-opiate receptors in the GI tract, blocking intestinal smooth muscle relaxation caused by opiates and thereby reversing opiate-induced slowing of GI transit time.1 2 4

  • Does not readily cross blood-brain barrier; therefore, does not affect opiate analgesic activity or precipitate opiate withdrawal, unlike centrally active opiate antagonists (e.g., naltrexone, naloxone).1 2 3 4 5 7 8 9 11 12 13

  • Exhibits greater affinity for μ-opiate receptors than for κ-opiate receptors; does not interact with δ-opiate receptors nor substantially bind to nonopiate receptors.9 12 13

  • 2–4% of the opiate antagonist activity and potency of naloxone;13 possesses some μ-receptor agonist activity.6 12 13

Commonly used brand name(s)

In the U.S.

  • Relistor

Available Dosage Forms:

  • Tablet

Therapeutic Class: Gastrointestinal Agent

Pharmacologic Class: Methylnaltrexone

Before Using methylnaltrexone bromide

In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For methylnaltrexone bromide, the following should be considered:


Tell your doctor if you have ever had any unusual or allergic reaction to methylnaltrexone bromide or any other medicines. Also tell your health care professional if you have any other types of allergies, such as to foods, dyes, preservatives, or animals. For non-prescription products, read the label or package ingredients carefully.


Appropriate studies have not been performed on the relationship of age to the effects of methylnaltrexone in the pediatric population. Safety and efficacy have not been established.


Appropriate studies performed to date have not demonstrated geriatric-specific problems that would limit the usefulness of methylnaltrexone in the elderly. However, elderly patients are more likely to have diarrhea and have kidney or liver problems, which may require caution and an adjustment in the dose for patients receiving methylnaltrexone bromide.


Pregnancy Category Explanation
All Trimesters C Animal studies have shown an adverse effect and there are no adequate studies in pregnant women OR no animal studies have been conducted and there are no adequate studies in pregnant women.

Breast Feeding

There are no adequate studies in women for determining infant risk when using this medication during breastfeeding. Weigh the potential benefits against the potential risks before taking this medication while breastfeeding.

Interactions with Medicines

Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are taking methylnaltrexone bromide, it is especially important that your healthcare professional know if you are taking any of the medicines listed below. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.

Using methylnaltrexone bromide with any of the following medicines is usually not recommended, but may be required in some cases. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.

  • Morphine
  • Morphine Sulfate Liposome
  • Naldemedine
  • Naloxegol
  • Oxycodone
  • Oxymorphone

Interactions with Food/Tobacco/Alcohol

Certain medicines should not be used at or around the time of eating food or eating certain types of food since interactions may occur. Using alcohol or tobacco with certain medicines may also cause interactions to occur. Discuss with your healthcare professional the use of your medicine with food, alcohol, or tobacco.

Other Medical Problems

The presence of other medical problems may affect the use of methylnaltrexone bromide. Make sure you tell your doctor if you have any other medical problems, especially:

  • Crohn's disease or
  • Diverticulitis or
  • Ogilvie's syndrome (decreased movement of food in the intestines) or
  • Peptic ulcer or
  • Stomach or bowel cancer—May increase risk for more serious side effects.
  • Kidney disease, moderate and severe or
  • Liver disease, moderate and severe—Use with caution. The effects may be increased because of slower removal of the medicine from the body.
  • Stomach or bowel blockage—Should not be used in patients with these conditions.