A modified cold stimulation technique for the evaluation of analgesic activity in human volunteers.

This report describes the effects of a modified cold pressure technique (MCP) on the dominant hand of 6 healthy right-handed volunteers, after single p.o. doses of codeine (60 mg), aspirin (1 g) and placebo in a cross-over, double-blind design. The method employed 9 serial tests on each study day, involving 5 consecutive 2 min periods of hand immersion in an equilibrating bath at constant temperature (37 degrees C), followed by a stimulating bath (0 degree C +/- 0.5) containing 15% ethylene glycol. For better control of peripheral circulatory temperature changes, a blood pressure cuff was inflated to 20 mm Hg below diastolic BP on the right upper arm, thereby preventing venous return from the lower arm during MCP stimulation. Although the test population was relatively small, the results showed a difference between aspirin, codeine and placebo. Codeine was statistically different from placebo (P less than 0.05). It is concluded that this modified technique offers a stable and sensitive method for the early assessment of analgesic activity.