[Opioid-Induced Constipation in Patients with Cancer Pain]

Opioids are effective in cancer pain management. However, adverse effects such as opioid-induced constipation(OIC) cause significant reductions in the quality-of-life of cancer patients. In addition, this treatment sometimes also results in inadequate pain relief. It is estimated that from 50-90% of cancer patients receiving opioids suffer from OIC. The mechanism of exogenous opioids on gastrointestinal opioid receptors is known to lead to bowel dysfunction: including motility, secretion and coordination of the sphincter function. The Rome Ⅳ criteria is widely used for the definition of OIC. Imaging, which is not routinely performed, is useful for diagnosing the severity and they also help in choosing the most appropriate laxatives. Additionally, the bowel function index (BFI)can help to distinguish between opioid-treated patients with or without constipation. Unfortunately, the effective Japanese scale for the BFI remains to be elucidated. Primary treatment with stimulants and osmotic laxatives often demonstrates limited effectiveness. New agents, such as peripherally acting mu-opioid receptor antagonists(PAMORA), which have a potent competitive antagonist action, are therefore needed to improve the treatment of such patients. PAMORA should be observed carefully for the diarrhea when the duration of opioid therapy is prolonged prior to PAMORA initiation. Pharmacologically, this diarrhea might be associated with the onset of peripheral withdrawal symptoms.