Article date: January 2002
By: J. A. Sutton, W. P. Gillin, T. J. Grattan, G. D. Clarke, S. G. Kilminster, in Volume 53, Issue 1, pages 43-47
Aims To discover whether a new infra‐red laser method could detect a change in pain threshold after as mild an analgesic as paracetamol and whether an effervescent liquid formulation produced a faster onset of action than tablets.
Methods This double‐blind, placebo controlled randomized study used a portable, infra‐red laser to measure ‘first pain’ thresholds on the nondominant forearm in 12 normal volunteers before and after 1 g of paracetamol or placebo. The mean of six recordings was determined three times before dosing, the first being used as a familiarization procedure, and 14 times after dosing.
Results We detected a small (2%), statistically significant difference in pain threshold between a liquid formulation of paracetamol and placebo at 30 and 60 min (P = 0.004 and P = 0.001), but not between tablets and placebo. Liquid also increased the threshold significantly compared with tablets at 60 min (P = 0.01).
Conclusions To detect such a small increase in pain threshold requires a highly consistent measure and the coefficient of variation was 2% for the study overall, surprisingly low for a subjective phenomenon. The reasons for this include minimizing reflectance by blacking the skin, using a nonhairy site, averaging six data points at each sample time and controlling closely the ambient conditions and the subjects' preparation for studies.
DOI: 10.1046/j.0306-5251.2001.01527.x
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