Covalently Loaded Naloxone Nanoparticles as a Long-Acting Medical Countermeasure to Opioid Poisoning

Andrew J. Kassick, Mariah Wu, Diego Luengas, Mohammad Ebqa'Ai, L. P. Tharika Nirmani, Nestor Tomycz, Toby L. Nelson, Marco Pravetoni, Michael D. Raleigh, Saadyah Averick

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8 Scopus citations


The mu opioid receptor antagonist naloxone has been a vital, long-standing countermeasure in the ongoing battle against opioid use disorders (OUD) and toxicity. However, due to its distinctive short elimination half-life, naloxone has shown diminished efficacy in cases of synthetic opioid poisoning as larger or repeated doses of the antidote have been required to achieve adequate reversal of severe respiratory depression and prevent episodes of renarcotization. This report describes the synthesis, characterization, and in vivo evaluation of a novel, nanoparticle-based naloxone formulation that provides extended protection against the toxic effects of the powerful synthetic opioid fentanyl. The strategy was predicated on a modified two-step protocol involving the synthesis and subsequent nanoprecipitation of a poly(lactic-co-glycolic acid) polymer scaffold bearing a covalently linked naloxone chain end (drug loading ∼7% w/w). Pharmacokinetic evaluation of the resulting covalently loaded naloxone nanoparticles (cNLX-NP) revealed an elimination half-life that was 34 times longer than high dose free naloxone (10 mg/kg) in male Sprague-Dawley rats. This enhancement was further demonstrated by cNLX-NP in subsequent in vivo studies affording protection against fentanyl-induced respiratory depression and antinociception for up to 48 h following a single intramuscular injection. These discoveries support further investigation of cNLX-NP as a potential therapeutic to reverse overdose and prevent renarcotization from fentanyl and its potent analogs.

Original languageEnglish (US)
Pages (from-to)1654-1664
Number of pages11
JournalACS Pharmacology and Translational Science
Issue number5
StatePublished - Oct 8 2021

Bibliographical note

Funding Information:
We gratefully acknowledge the National Institutes of Health, National Institute of Drug Abuse and the CounterACT program (R21DA050565) for funding. NMR measurements and instrumentation at CMU, which was partially supported by the NSF (CHE-0130903 and CHE-1039870).

Publisher Copyright:


  • Drug Delivery
  • Fentanyl
  • Naloxone
  • Nanoparticles
  • Opioids
  • Renarcotization


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