Methylnaltrexone bromide
Class: Peripherally acting opioid-receptor antagonist
Indications: Opioid-induced constipation where oral and rectal treatments are ineffective or not tolerated
Contraindications/cautions: Contraindications: acute surgical abdomen, gastrointestinal obstruction, post-operative ileus. Cautions: active diverticulitis, faecal impaction, conditions or concomitant medications affecting the structural integrity of the GIT (cancer, peptic ulcer, NSAIDs), โ risk of perforation, patients with colostomy or peritoneal catheter
Adverse reactions: abdominal pain, diarrhoea, flatulence, vomiting, nausea, dizziness, hyperhidrosis, opioid withdrawal symptoms (usually mild), injection site reactions. Rare: GI perforation
Metabolism/clearance: minimally metabolised and predominantly excreted unchanged
Interactions: Nil reported
| Dosing: | |
|---|---|
| Adult: | under 38 kg โ 150 micrograms/kg 38 to 62 kg โ 8 mg (=0.4 mL) 62 to 114 kg โ 12 mg (=0.6mL) Over 114 kg โ 150 micrograms/kg |
Given once daily on alternate days โ dose can be repeated after 24 hours if no bowel movement occurs. Inject into upper arm, abdomen or thigh; rotate sites and avoid areas that are tender, bruised, red or hard
Syringe driver: not available
Mechanism of action: Binds to mu-opioid receptor in the GIT (8-fold affinity for mu receptor over kappa receptor), blocking constipating effects of opioids. Limited ability to cross the blood brain barrier so does not antagonise opioid analgesia
Onset: May work within 30 minutes after subcut injection
Notes:
- hepatic impairment: mild to moderate hepatic impairment โ no dose adjustment necessary; no information available for use in severe hepatic impairment โ advice is to avoid use
- renal impairment: if eGFR < 30 mL/min/1.73m^2 , halve the dose; avoid in end stafe renal failure requiring dialysis (no information available)
Availability: Vial 12 mg/0.6 mL