6β Naltrexol

6β-Naltrexol, or 6α-hydroxynaltrexone, is a major active metabolite of naltrexone formed by hepatic dihydrodiol dehydrogenase which acts as a potent, peripherally selective opioid neutral antagonist. Relative to naltrexone, 6β-naltrexol has about half the affinity for the μ-opioid receptor, but is present at approximately 10–30-fold higher concentrations at steady state due to extensive first-pass metabolism of the parent drug. 6β-Naltrexol was itself investigated as an opioid antagonist, specifically for the treatment of opioid-induced constipation, and was found to be effective and well-tolerated, but was not further pursued.