A new method for the evaluation of analgesic activity using adjuvant-induced arthritis in the rat.

A bioassay was developed for the assessment of analgesic activity by using pain resulting from a reproducible pathological condition. The vocalization displayed by rats with adjuvant-induced polyarthritis was defined as an expression of pain, and a decrease of this response was established as specifically demonstrating analgesic activity. This method was capable of detecting the analgesic activity of morphine-like and narcotic antagonist-type analgesics, as well as the activity of the antipyretic analgesics. The relative potencies of known analgesic agents determined with this technique closely approximated the potencies of these analgesics in man. The instrumentation for recording and measuring the vocal response of arthritic rats is described.