Naloxone-reversible analgesic action of SKF 525-A in mice

SKF 525-A, given i.p. to mice at doses from 50 to 100 mg/kg, had analgesic activity approximately 40% the analgesic potency of d-propoxyphene HCl, a chemically similar narcotic. While the analgesia produced by propoxyphene was totally antagonized by naloxone, however, that produced by SKF 525-A was only partly reversed. We suspect that SKF 525-A may exert its antinociceptive actions partly by an interaction with CNS narcotic receptors and partly by a nonspecific sedating action.