IngentaConnect A new laser pain threshold model detects a faster onset of action...

Authors: Sutton J.A.; Gillin W.P.; Grattan T.J.; Clarke G.D.; Kilminster S.G.

Source: British Journal of Clinical Pharmacology, Volume 53, Number 1, January 2002 , pp. 43-47(5)

Abstract:

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.

Keywords: consistency of laser pain threshold; paracetamol liquid vs tablet formulations

Language: English

Document Type: Research article

DOI: 10.0000/135048598354898

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A new laser pain threshold model detects a faster onset of action from a liquid formulation of 1 g paracetamol than an equivalent tablet formulation