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Methylnaltrexone
Opioid-induced Constipation for Non-Cancer Pain
In August 2011, the U.S. Food and Drug Administration (FDA) accepted for filing a supplemental New Drug Application (sNDA) for RELISTOR (methylnaltrexone bromide) Subcutaneous Injection to treat opioid-induced constipation in patients with non-cancer pain. The FDA issued an action date of April 27, 2012 under the Prescription Drug User Fee Act (PDUFA).
If approved, RELISTOR will be the first FDA-approved medicine to treat the underlying cause of OIC experienced by the millions of patients taking opioids for non-cancer pain.
About Opioid-induced Constipation in the Chronic Pain Setting
Opioids are analgesics -- drugs used to relieve pain or achieve analgesia. Approximately 10 million patients a year in the U.S. are prescribed opioids for 30 days or more to manage pain1. Opioids provide powerful pain relief, but also cause significant constipation. In a multinational internet-based survey of 322 patients with chronic pain taking daily oral opioids and laxatives, 81% of patients reported experiencing constipation while using their current opioid regimen and 45% reported less than 3 bowel movements per week2.
How methylnaltrexone works
Opioids relieve pain by interacting with receptors located in the brain and spinal cord, which comprise the central nervous system (CNS). At the same time, opioids also activate receptors outside the CNS, such as those in the gastrointestinal tract, often resulting in constipation.
Methylnaltrexone, a selective, peripherally acting, mu-opioid-receptor antagonist, decreases the constipating effects of opioids without diminishing the analgesic effects of opioids in the CNS. Because of its positive charge, methylnaltrexone has restricted ability to cross the blood-brain barrier. It reverses the peripheral action of opioids without affecting centrally-mediated pain relief.
As a result, methylnaltrexone decreases the constipating effects on the gastrointestinal tract via receptors outside the CNS without affecting centrally mediated analgesia (i.e., pain relief) via receptors inside the CNS.
1 SDI Longitudinal Patient Data Year 2005
2 The Prevalence, Severity, and Impact of Opioid-Induced Bowel Dysfunction: Results of a US and European Patient Survey (PROBE 1) Bell, et al., Jnl. Pain Medicine 2009; vol. 10, no. 1, p. 40