Bioabsorbable, subcutaneous naltrexone implants mitigate fentanyl‐induced respiratory depression at 3 months—A pilot study in male canines

The aim of this study is to determine if extended-release, bioabsorbable, subcutaneous naltrexone (NTX) implants can mitigate respiratory depression after an intravenous injection (IV) of fentanyl. Six different BIOabsorbable Polymeric Implant Naltrexone (BIOPIN) formulations, comprising combinations of Poly-d,l-Lactic Acid (PDLLA) and/or Polycaprolactone (PCL-1 or PCL-2), were used to create subcutaneous implants. Both placebo and naltrexone implants were implanted subcutaneously in male dogs. The active naltrexone implants consisted of two doses, 644 mg and 1288 mg. A challenge with IV fentanyl was performed in 33 male dogs at 97-100 days after implantation. Following the administration of a 30 μg/kg intravenous fentanyl dose, the placebo cohort manifested a swift and profound respiratory depression with a ~50% reduction in their pre-dose respiratory rate (RR). The BIOPIN NTX-implanted dogs were exposed to escalating doses of intravenous fentanyl (30 μg/kg, 60 μg/kg, 90 μg/kg, and 120 μg/kg). In contrast, the dogs implanted with the BIOPIN naltrexone implants tolerated doses up to 60 μg/kg without significant respiratory depression (<50%) but had severe respiratory depression with fentanyl doses of 90 μg/kg and especially at 120 μg/kg. Bioabsorbable, extended-release BIOPIN naltrexone implants are effective in mitigating fentanyl-induced respiratory depression in male canines at about 3 months after implantation. This technology may also have potential for mitigating fentanyl-induced respiratory depression in humans.