D-cycloserine in the Management of Chronic Low Back Pain

Human brain imaging studies indicate that the medial prefrontal cortex activity can predict more than 80% of the variance of chronic back pain intensity. Therefore, the investigators have hypothesized that modulation of brain activity at this site should result in analgesia. D-cycloserine has been shown to potentiate conditioned fear extinction. Based on this the investigators hypothesize that chronic neuropathic pain (back pain with radiculopathy) is partially mediated or potentiated by decreased ability to extinguish the pain memory, which the investigators hypothesize to be mediated through reward/aversion brain circuitry, and specifically through medial prefrontal cortex. They have tested this idea in pre-clinical studies and demonstrated that rats with neuropathic pain show analgesia over the long-term when treated with D-cycloserine. In humans with chronic back pain, the investigators hypothesize that D-cycloserine will enhance extinction of back pain which in turn should result in reduced emotional relevance of the pain, that is reduced suffering. It is quite possible that the overall intensity of the back pain will be unaffected, however, the associated suffering will be significantly attenuated. This will be a double-blind, randomized, parallel group escalating dose study comparing D-cycloserine twice a day (bid) with placebo bid in patients with chronic low back pain. Subjects meeting inclusion criteria will continue baseline medications and be treated for 12 weeks with study drug: 50 mg bid DCS or matching placebo for the first 4 weeks, then 100mg bid DCS or matching placebo for 4 weeks and finally 200mg bid DCS or matching placebo for 4 weeks. Assessments of efficacy and safety will be undertaken every 2 weeks using standard, validated instruments to evaluate change in pain, function, quality of life and adverse events.