A major clinical use is in the management of acute opioid overdose. Naloxone and nalmefene are given intravenously. Because naloxone has a short duration of action (1–2 h), multiple doses may be required in opioid analgesic overdose. Nalmefene has a duration of action of 8–12 h. Naltrexone has a long elimination half-life, blocking the actions of strong agonists (eg, heroin) for up to 48 h after oral use.