Nalmefene: blockade of intravenous morphine challenge effects in opioid abusing humans

No studies have assessed the dose-effect or duration of opioid blockade in opioid abusers produced by oral nalmefene, a micro-opioid antagonist. The present study examined the profile and time course of oral nalmefene blockade of subjective and physiological effects produced by intravenous morphine. To assess these effects, seven opioid abusers received oral nalmefene (0, 50 and 100 mg) followed by intravenous morphine (0, 10 and 20 mg) challenges every 24 h for 96 h using a Latin square randomized cross-over design. The duration of blockade varied by measure and dose. Both 50 and 100 mg nalmefene blocked morphine's effects up to 48 h.