Methylnaltrexone bromide (Relistor) is a peripherally-acting mu-opioid receptor antagonist and is designed to relieve the side effects of constipation (a side effect of opioids) without interfering with pain relief in the central nervous system.
It is licensed in the UK as a subcutaneous injection for use in adult palliative care when patients have failed to respond to conventional laxative therapy.
Recently published data in the New England Journal of Medicine showed that patients who suffer with opioid-induced constipation were significantly more likely to experience a bowel movement within four hours of receiving one dose of methylnaltrexone bromide when combined with laxative therapy versus laxative therapy plus placebo (Thomas et al, 2008).
Opioids bind to receptors in the gut and can slow down movement in the bowel leading to constipation. There is also a reduction in the amount of mucus secretions produced by the bowel and an increase in absorption of fluids which increases the problem. OIC can cause pain, nausea and vomiting and faecal impaction. It is distress for patients and can be difficult to manage.
Thomas J et al (2008) New England Journal of Medicine; 358: 2332-43