methylnaltrexone bromide at a glance
Medicine class
Peripherally acting mu-opioid receptor antagonist.
Usual role
Opioid-induced constipation in adults whose response to laxatives is insufficient.
Administration
Injection under the skin; food does not affect administration.
Practical point
A bowel movement may occur quickly, so remain near a toilet after injection.
What is methylnaltrexone bromide used for?
The selected UK product is licensed for:
Treating opioid-induced constipation in adults when laxative treatment has not provided a sufficient response, including adults with chronic pain or advanced illness.
How does methylnaltrexone bromide work?
Opioids activate mu receptors in the bowel, slowing movement and promoting constipation. Methylnaltrexone bromide blocks these receptors mainly outside the brain, helping restore bowel activity while generally preserving centrally mediated pain relief.
methylnaltrexone bromide preparations and strengths
Injection
Route: Parenteral
Strengths: 8 mg, 12 mg, 12 mg/0.6 mL
How to take methylnaltrexone bromide
Use the subcutaneous injection exactly as demonstrated by a healthcare professional. It may be administered with or without food.
Suitable injection areas are the thighs, abdomen and, when another person gives the injection, upper arms.
Rotate injection sites.
Avoid skin that is tender, bruised, red or hard and areas with scars or stretch marks.
Stay near a toilet because bowel activity may begin rapidly.
methylnaltrexone bromide side effects
Common or expected effects
- Abdominal pain
- Nausea
- Diarrhoea
- Flatulence
- Vomiting
- Dizziness
- Injection-site pain, burning, redness or swelling
- Opioid-withdrawal-like symptoms such as chills, sweating, tremor, flushing, runny nose or palpitations
Get urgent medical advice
- Severe, persistent or worsening abdominal pain, potentially indicating gastrointestinal perforation
- Severe or persistent diarrhoea
- Marked opioid-withdrawal symptoms or reduced pain control, particularly where the blood–brain barrier may be disrupted
methylnaltrexone bromide in pregnancy
Human pregnancy data are inadequate and the potential risk is uncertain. The UK product information advises use only when clearly necessary, following a prescriber-led assessment of benefits and risks.
methylnaltrexone bromide while breastfeeding
It is unknown whether methylnaltrexone bromide enters human milk, and direct infant-safety evidence is unavailable. The decision whether to continue breastfeeding or treatment requires individual review of the benefits to the child and mother.
methylnaltrexone bromide interactions
Methylnaltrexone bromide has limited recognised pharmacokinetic interaction potential, but the full medication list should still be reviewed.
Cimetidine
It reduces renal clearance of methylnaltrexone bromide, but the studied change in overall exposure was not clinically meaningful.
Medicines metabolised by cytochrome P450 enzymes
Clinically significant effects are unlikely because methylnaltrexone bromide is minimally metabolised by, and generally does not inhibit, these enzymes.
Common questions about methylnaltrexone bromide
Answers are fully visible for fast scanning and source review.
How quickly can methylnaltrexone bromide work?
Bowel movement can occur rapidly; clinical-trial data suggest an average onset of about 30–60 minutes, although individual responses vary.
Does methylnaltrexone bromide reduce opioid pain relief?
It is designed to act mainly outside the brain, so central pain relief is generally preserved. Withdrawal symptoms or reduced analgesia can nevertheless occur, particularly if the blood–brain barrier is disrupted.
Sources
These sources were used to prepare and review this medicine page.
Prepared and reviewed by the iatroX editorial team.