Methylnaltrexone: its pharmacological effects alone and effects on morphine in healthy volunteers

Rationale Methylnaltrexone bromide (MTNX) is a peripherally acting mu-opioid receptor antagonist, prescribed for the treatment of opioid-induced constipation in patients with advanced illness who are receiving palliative care. Studies have used this drug to determine if other opioid-induced effects besides constipation are altered by MTNX in humans and have suggested, based on their results, that these other effects are altered by peripheral opioid actions.