Effect of various types of analgesic drugs on an experimental model of chronic inflammatory pain in mice

We attempted to develop an experimental model of chronic inflammatory pain in mice. The mice were injected intradermally at the base of the tail with various kinds of irritants (yeast, carrageenin, mustard and adjuvant). The pain threshold was measured by the pressure method every 60 min for 5 hr and once a day at the same time throughout the experimental period. The group of 10% yeast-injected mice exhibited the most intensive hyperalgesia. The analgesic effect of various types of analgesic drugs were studied, comparing the effects in normal mice and various kinds of irritants-induced hyperalgesia mice. It was demonstrated by observing ED50 values that nonsteroidal antiinflammatory drugs (NSAIDs), narcotic analgesic drugs and agonist/antagonist type of analgesic drugs were effective, but CNS-acting drugs were ineffective in yeast hyperalgesia mice. In comparison with yeast hyperalgesia mice, larger doses of analgesic drugs were required in normal mice and other irritants-treated mice. Especially, acidic NSAIDs were more effective in yeast hyperalgesia mice than normal mice. It was suggested that acidic NSAIDs specifically inhibit inflammatory pain. Moreover, yeast hyperalgesia mice are useful for the quantitative measurement of analgesic drugs.