Peripheral μ-opioid receptor antagonist
Methylnaltrexone bromide
Brand names: Relistor
Adult dose
Dose: Weight-based SC every other day (8mg if 38–61kg, 12mg if 62–114kg); refer to BNF
Route: SC
Frequency: alternate days
Clinical pearls
- Opioid-induced constipation in advanced illness when standard laxatives have failed
- Does not cross BBB — preserves analgesia
Contraindications
- Bowel obstruction (mechanical)
- Acute abdomen
- Faecal impaction (until resolved)
Side effects
- GI cramps/diarrhoea
- GI perforation (very rare — caution in conditions weakening GI wall)
- Flatulence
Monitoring
- Bowel function
- Abdominal pain
Reference: BNF; NICE TA651; SmPC; https://bnf.nice.org.uk/drugs/methylnaltrexone-bromide/. Verify against your local formulary and the latest BNF before prescribing.
Related
Curated clinical cross-links plus same-class fallbacks.
Calculators
- Morphine Milligram Equivalents (MME) Calculator · Pain / Opioids
- Opioid Conversion / Equianalgesic Guide · Pain Management
- Numeric Rating Scale (NRS) Pain Assessment and Management · Pain Management
- HINTS Plus (Central vs Peripheral Vertigo) · Vertigo / Dizziness
- Carpal Tunnel Syndrome-6 (CTS-6) Diagnostic Tool · Peripheral Nerve
- Peripheral Blood Stem Cell (PBSC) Collection Target Calculator · Stem Cell Transplant
Drugs
Pathways
- Lower Gastrointestinal Bleed · BSG 2019; NICE NG141
- Variceal Upper GI Bleed · BSG 2015; Baveno VII (2022)
- Spontaneous Bacterial Peritonitis (SBP) · BSG / EASL 2018
- Hepatorenal Syndrome · EASL 2018; ICA 2015
- Hepatic Encephalopathy · EASL 2014; West Haven criteria
- Clostridioides difficile Colitis · NICE NG199 (2021); IDSA/SHEA 2021