Methylnaltrexone (Relistor)

A quarternary amine, a mu-opioid-receptor antagonist given subcutaneously for opioid induced constipation.

Opioid analgesics lead to constipation via their effect on intestinal smooth muscle and interference with normal bowel elimination.

Indicated for the treatment of opioid-induced constipation in patients with advanced illness who are receiving palliative care, when response to laxative therapy has not been sufficient.

A mu-opioid receptor antagonist with limited ability to cross the blood brain barrier.

Blocks effects of opioid in peripheral tissues, including the gastrointestinal tract.

Does not interfere with central nervous system mediated analgesic effects.

In severe renal insufficiency the dose should be reduced by 50%.

Contraindicated in the presence of gastrointestinal mechanical obstruction.

Administered as a subcutaneous injection.

Usual schedule is one dose every other day, as needed, but no more frequently than one dose in a 24-hour period.

The recommended dose is 8 mg for patients weighing 38 to less than 62 kg or 12 mg for patients weighing 62 to 114 kg.

Methylmalonaltrexone normalizes bowel movements in opioid induced constipation and reduces the need for laxatives, but is also frequently associated with non-serious adverse effects, including abdominal pain, flatulence, and dizziness.

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