• Pain intensity measurements will be recorded twice daily, using McGill short form pain questionnaire on the PDA. The Visual Analog Pain Scale (VAS) will serve as the primary outcome measure. [ Time Frame: Study completion (16 weeks) ] [ Designated as safety issue: No ]
  

Neuropathic pain is a complex and likely heterogeneous disorder, and we recognize that clinically useful agents such as opioids, gabapentin, and antidepressants may be effective precisely because they have multiple mechanisms of action at multiple sites. This study, however, will not only provide important mechanistic information regarding one cascade which can be manipulated for analgesia, but will also provide much needed systematic and practical guidance for multi-drug therapy in patients with neuropathic pain.

This study in patients with diabetic neuropathic pain, culminate in a quantitative description of interactions between activators of descending noradrenergic activity, norepinephrine transporter inhibitors, and cholinesterase inhibitors to exploit the plasticity of analgesia in chronic pain states. We will focus on practical applications, using clinically approved drugs, including gabapentin (Neurontin®) to activate noradrenergic activity, duloxetine (Cymbalta®) to inhibit the norepinephrine transporter, and donepezil (Aricept®), approved for the treatment of Alzheimer's dementia, but not previously tested to treat neuropathic pain, to inhibit cholinesterase.

After the baseline measurements and physical examination patients will be trained to use a Personal Digital Assistant (PDA) to answer questions about their diabetic neuropathic pain. Upon successful completion of these tasks the patients will be randomized to receive one of the drug choices or placebo (inactive pill).

The study will last for a total of 16 weeks and includes 5 visits to the research center with each visit lasting approximately 2 hours.