Brain Imaging of Lidoderm for Chronic Back Pain

Previous data showed that Lidoderm patches that contain 5% Lidocaine applied to the affected area for a period of 1-2 weeks decreased chronic pain. We conducted a preliminary open-label trial in chronic back pain patients and found that the patients reported reduction in pain intensity and associated brain activity (measured with fMRI). As a next step, we conducted a double blind clinical trial where the drug was tested against placebo to determine whether the effects on CBP were mediated by a pharmacological mechanism. For this we obtained psychophysical measurements of pain and measures of brain activity using fMRI. Two scans after treatment (6 hour and 2 weeks after treatment) were conducted to observe the effects of short term and long term use.

Brain activity was measured by the non-invasive method of functional imaging (fMRI), which enables examination of cortical blood flow during pain rating. These brain scans were acquired in chronic back pain patients while they rated their ongoing chronic pain using a finger span device. In a control task, each patient also rated the changes in the length of a bar n a screen (a visual control task). Anatomical scans were also acquired.

The general design of the study was that CBP subjects were assesses with fmri for brain responses for ongoing pain at three time points. The initial (baseline) scan occurred after a minimum of 48 hour period during which the patients refrained from taking analgesic medication. The patients were next scanned at 6 hours after treatment and again after 2 weeks of continuous treatment. Subjects were randomised to placebo or Lidoderm (both Lidoderm and placebo patches were supplied by Endo Pharmaceuticals).