2.8. CFA‐induced inflammatory pain

The CFA‐induced inflammatory pain was assessed in male Sprague‐Dawley rats (Charles River Laboratories Japan) using von Frey filaments (Stoelting Co). Fifty percent of CFA was injected into the plantar surface of the right hind paw at a volume of 0.1 mL, and 5 days later, the paw withdrawal threshold (PWT) was determined by the up‐down method described in Chaplan et al (1994).29 PKM‐833 at doses of 0.3, 1, and 3 mg/kg or naproxen at a dose of 15 mg/kg was orally administered 1 or 4 hours before the measurement of PWT, respectively.