Pain as a result of nerve injury (neuropathic pain) is a particularly severe form of chronic pain. Common examples of neuropathic pain are pain due to diabetes and shingles. There is good evidence that an intravenous infusion of lidocaine (local anesthetic) is useful for the management of neuropathic pain in the short term - up to six hours.

This study will examine the role of intravenous lidocaine in the relief of neuropathic pain over four weeks following infusion compared to an active placebo infusion of diphenhydramine(Benadryl) in normal saline. If we can show that intravenous lidocaine provides sustained benefit for up to one month, this will be a major advance in the management of individuals suffering from neuropathic pain.

Inclusion Criteria:

• Chronic neuropathic pain due to diabetes mellitus or herpes zoster and a score of 4/10 or greater on the DN4 questionnaire.
• Moderate to severe pain as defined by screening average pain intensity of 5 or greater on a 0-10 numerical rating scale.
• Neuropathic pain duration of at least 6 months.

Exclusion Criteria:

• Presence of clinically significant cardiac disease.
• Poorly controlled seizure disorder.
• Significant psychiatric disorder.
• History of allergy to lidocaine or any other amide local anesthetic
• History of allergy to diphenhydramine.
• Prior treatment with a local anesthetic infusion.
• Neuropathic pain due to cancer or complex regional pain syndrome
• Language barrier or cognitive impairment that would preclude understanding of the study and filling out of questionnaires
• Lack of a driver to transport the patient to and from the pain clinic.