Emerging treatments
Nalmefene
Nalmefene, a 6-methylene analogue of naltrexone, is an opioid antagonist that prevents or reverses the effects of opioids (including respiratory depression, sedation, and hypotension). Nalmefene has a longer duration of action than naloxone at fully reversing doses and has no opioid agonist activity.[80] Nalmefene has been approved by the US Food and Drug Administration (FDA) for the complete or partial reversal of opioid drug effects and is available as both an injection (including an auto-injector) and intranasal spray. The intranasal spray is approved for the emergency management of known or suspected opioid overdose in both hospital settings and community use. In one recent study, looking at reversing the respiratory effects of fentanyl using either naloxone or nalmefene, it appeared that intramuscular nalmefene achieved reversal of fentanyl-induced respiratory depression similar to or better than that achieved with standard-of-care naloxone treatments.[81] Nalmefene is likely to be used as an alternative to naloxone; however, guidelines do not recommend it replace naloxone.[82][83] It also is not approved for alcohol or opioid use disorder as a maintenance treatment.[84] Nalmefene is not approved in Europe for this indication.
CSX-1004
CSX-1004 is an investigational human immunoglobulin G1 monoclonal antibody specific for fentanyl and fentanyl analogues. It works by sequestering fentanyl molecules as they enter the bloodstream, effectively neutralising them in the blood before they reach the brain and preventing them from exerting their harmful effects. The FDA has granted fast-track designation to CSX-1004 for the prevention of fentanyl- and fentanyl analogue-related overdose.[85] It is the first clinic-ready, fully human monoclonal antibody with affinity for fentanyl and related analogues. In mice, CSX-1004 reversed fentanyl antinociception and the intractable respiratory depression caused by carfentanil.[85]
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