Antinociceptive activity of intracisternally and intrathecally administered eptazocine, a novel analgesic, in mice.

Antinociceptive potency of eptazocine (1-1,4-dimethyl-10-hydroxy-2,3,4,5,6,7-hexahydro-1,6-methano-1H-4-ben zazonine), a novel analgesic derived from homobenzomorphan, was compared with that of morphine and pentazocine after intracisternal and intrathecal administration into conscious mice using acetic acid-induced writhing, tail pressure and hot plate tests. The rank order of potency for inhibition of writhing after intracisternal administration was morphine greater than eptazocine greater than pentazocine. In contrast, the intrathecal compounds inhibited writhing with a rank order of potency of eptazocine greater than or equal to morphine greater than pentazocine. On the tail pressure and hot plate tests after intrathecal administration, ED50 ratios of eptazocine to morphine were much smaller than that on the writhing test. Systemic naloxone did not antagonize the antinociceptive effect of intrathecal eptazocine on the writhing test. These results suggest that the antinociceptive action of eptazocine is rather specific to chemical nociceptive stimuli and may be mediated via spinal non mu-opioid receptors in the mouse.