Pathophysiology, diagnosis, and management of opioid-induced constipation.

Opioids are potent analgesics used for the treatment of acute and chronic pain. Side-effects are common and among the most bothersome are those associated with opioid-induced bowel dysfunction, which includes opioid-induced constipation. In this Review, we provide a summary of the pathophysiology, diagnosis, and management of opioid-induced constipation, which can be defined as a change in baseline bowel habit or defecatory patterns following initiation, alteration, or increase of opioid therapy. Opioid-induced constipation is a consequence of the action of opioids on their receptors in the gastrointestinal tract. A comprehensive clinical assessment is beneficial, including evaluation of the patient's understanding of their constipation and underlying condition for which opioids are used. Clinical assessment should also aim to differentiate opioid-induced constipation from pre-existing constipation exacerbated by the opioids. Preventive strategies need to be considered when patients start treatment with opioids, such as lifestyle changes. First-line management includes simple over-the-counter laxatives. The bowel function index can be useful to objectively identify patients who are refractory to these initial measures. In this context, alternative over-the-counter laxatives (or combinations of laxatives), secretogogues, or peripherally acting μ-opioid receptor antagonists might also be considered. Educational strategies need to be developed to improve the knowledge base of health-care providers on the identification and management of opioid-induced constipation.