Restoring The Mechanical Properties of the Respiratory System as a Treatment of Fentanyl Overdose-Induced Hypoventilation using Kappa Agonists

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ABSTRACT Mu-opioid agonist overdose is associated with immediate and prolonged tetanic and rhythmic contractions of the inspiratory and expiratory muscles that impede respiratory movements for hours. This effect, referred to as opioid induced chest wall rigidity, is a critical mechanism contributing to the lethality of opioid-induced hypoventilation. Mu-opioid-induced muscle “rigidity” is produced by neurons in the locus coeruleus and can be suppressed by kappa-opioid receptor agonists, but not by current ventilatory stimulants. The objective of our proposal is to demonstrate, following an overdose by the mu-opioid receptor agonist fentanyl, that kappa-opioid receptor agonists 1- restore the alteration of passive respiratory mechanics and suppress the hypermetabolism produced by fentanyl induced muscle rigidity, 2- prevent a fatal outcome in unsedated rats. We will test nalfurafine, the only commercially available kappa agonist, and show that it counteracts the ventilatory effects of a fentanyl overdose. If efficacy is demonstrated in rodents, we will pursue these efficacy studies in non-anesthetized large mammal models and will test intravenous as well as intranasal route. Our ultimate goal is to obtain FDA approval for nalfurafine as a treatment of mu-opioid receptor agonist-induced hypoventilation, treatment that could be used in indications ranging from mass casualty to individual victims of opioid intoxication.