Determination of antinociceptive efficacy of drugs in mice using different water temperatures in a tail-immersion test.

A variety of analgesic drugs were tested for their ability to alter the response to noxious stimuli of differing severity in an attempt to develop a procedure to evaluate differences in efficacy of different analgesics. The severity of a noxious stimuli delivered to mice was varied by immersing the mouse tails in water maintained at 45, 50, 55 degrees C. As has been previously observed, the opiate analgesics morphine and nalorphine were active at all temperatures. Pentazocine was active at 45 and 50 degrees C, but not at 55 degrees C. The cyclooxygenase inhibitors tested showed a wide variety of activity. Naproxen was active at all temperatures. Zomepirac was active at 45 and 50 degrees C, but not 55 degrees C. Acetaminophen, ibuprofen, and fenoprofen were active at 45 degrees C, but not at higher temperatures. Aspirin and indomethacin were inactive at all temperatures tested. These results roughly paralleled the differences in the severity of pain for which these analgesics are effective.