Crossover Post-herpetic Neuralgia (PHN)

Allocation: Randomized Stratified

Interventional model: Cross-over Placebo Controlled

Inclusion criteria

• Patient with Post-Herpetic Neuralgia (PHN) as defined as pain present for more than 6 months after the onset of a herpes zoster skin rash affecting the trigeminal, cervical, thoracic, lumbar, or sacral regions.
• Based on patient diary information collected during the Baseline week (day -7 to randomization Day 1), patient has completed at least 5 diary entries and has an average weekly pain rating of at least 4 on the 11-point pain rating scale.
• The patient is able to satisfactorily complete, in the Investigator's judgment, the Cognitive Battery.
• Male or female, 18-85 years of age.

Exclusion criteria

• Other severe pain that may potentially confound pain assessment.
• History of complete lack of response to pregabalin (at least 300 mg qd for 4 weeks) or gabapentin (at least 1800 mg qd for 4 weeks).
• Hemoglobin A1c > 9%
• Hemoglobin ≤ 9 g/dL.
• Active herpes zoster or known viral infection.
• Previous neurolytic or neurosurgical therapy for PHN.
• Estimated glomerular filtration rate (eGFR) according to the re-expressed abbreviated (four-variable) Modification of Diet in Renal Disease (MDRD) Study equation ≤ 40ml/min/1.73m2.
• Patients who have been on a stable dose of anticonvulsant,anticholinergic, antiviral medications, nicotine replacements, or any other smoking cessation medications for <4 weeks prior to randomization. Patients who are on stable doses for => 4 weeks prior to randomization are allowed, however, there should be no adjustments to the dose of these medications during study.
• Patients currently on more than one drug for treatment of neuropathic pain (low dose opioids, antidepressants, or anticonvulsants). Patients are allowed to participate if on a stable dose for at least 4 weeks prior to randomization (Day1) and should remain stable during course of study.