Discovery of a long-acting nanocrystal formulation of INND-2201, a new co-drug of pregabalin and palmitoylethanolamide with synergistic analgesic effects.

Chronic pain is a global health problem affecting approximately 30% of the adult population worldwide. Currently available painkillers often showed limited efficacy or serious adverse effects and require frequent administration to maintain therapeutic effects. To develop new long-acting analgesics with synergistic antinociceptive effects, a new co-drug INND-2201 of pregabalin and palmitoylethanolamide (PEA) was synthesized, characterized and prepared as a nanocrystal formulation. INND-2201 was slowly metabolized into pregabalin and PEA in microsomal stability test, and oral INND-2201 exhibited significant and synergistic antinociceptive effects for inflammatory and neuropathic pain with ED50 values of 4.43 and 5.54 ​mg/kg, respectively. Nanocrystals (NCs) of INND-2201 were then prepared by the ball milling method with the particle size of 107.1 ​± ​2.7 ​nm. Intramuscular administration of INND-2201 ​NCs demonstrated prolonged pain relief lasting up to 5 days for chronic inflammatory pain in mice. Acute toxicity test, muscular irritation evaluation, rotarod test and open field test indicated that INND-2201 had a good safety profile. Taken together, INND-2201 ​NCs exerted long-acting analgesic effects and provided a promising strategy for the management of chronic pain.