Morphine-6-glucuronide (M6G) for postoperative pain relief.

Morphine-6-glucuronide (M6G) is morphine's active metabolite acting at the mu-opioid receptor. Recent experimental human studies and 5 of 6 randomized clinical trials indicate that M6G causes adequate and long lasting pain relief comparable to morphine. There are various observations that M6G is associated with a reduction in the severity of side effects normally associated with opioid use, such as reduced postoperative nausea and vomiting (PONV) and reduced respiratory depression. The present drug profile provides a review of the pharmacological properties of M6G, the clinical evidence relating to its efficacy and safety, and discusses its future role in the treatment of postoperative pain.