Products
Methylnaltrexone is commercially available as a solution for injection (Relistor). It has been approved in many countries since 2009.
Structure and properties
Methylnaltrexone (C21H26NO4, Mr = 356.4 g/mol) is an -methylated naltrexone. It is present in drugs as methylnaltrexone bromide.
Effects
Methylnaltrexone (ATC A06AH01) counteracts constipation caused by opioids. The effects are due to peripheral antagonism at μ-opioid receptors in the intestine. In contrast, the analgesic effects of opioids in the central nervous system are not affected because methylnaltrexone does not cross the blood–brain barrier due to its positive charge. The half-life is between 8 to 13 hours.
Indications
For the treatment of opioid-induced constipation in palliative care patients in whom usual laxative treatments are insufficiently effective.
Dosage
According to the SmPC. The drug is injected subcutaneously as needed. It is not a continuous therapy. Injections should be administered no more than once within 48 hours.
Contraindications
- Hypersensitivity
- Mechanical gastrointestinal obstruction
For complete precautions, see the drug label.
Interactions
Methylnaltrexone should not be combined with other opioid antagonists.
Adverse effects
The most common adverse effects include abdominal pain, nausea, and flatulence.
