This is a proof-of-concept study to determine if PH-797804 reduces neuropathic pain associated with post-herpetic neuralgia. Suitable patients will be randomized to receive either PH-797804 or placebo for 4 weeks, during which time they will also record their pain symptoms using various pain scales.

Inclusion Criteria:

• Male or female, at least 18 years of age
• Patients must have pain present for more than 3 months after healing of the Herpes zoster skin rash. There is no upper limit on the duration of PHN.
• Patients at screening visit (V1) must have a score ≥40 mm on the Pain Visual Analog Score (VAS).

Exclusion Criteria:

• Patients having other severe pain, which may impair the self-assessment of the pain due to post-herpetic neuralgia
• History within the previous year of: myocardial infarction, cardiac arrhythmia (e.g. atrial fibrillation, paroxysmal atrial fibrillation, atrial flutter, supraventricular tachycardia, ventricular tachycardia), left ventricular failure, New York Heart Association (NYHA) Class III-IV congestive heart failure requiring treatment, unstable angina, coronary angioplasty, coronary artery bypass grafting (CABG) or cerebrovascular accident (including transient ischemic attacks).
• Tuberculosis without treatment and/or positive tuberculin reaction to PPD (Purified Protein Derivative) without known (documented) vaccination with the bacilli Calmette-Guerin vaccine (BCG).
• A positive approved immunoassay/ELISA blood test for TB (e.g. TB T-SPOT™, QuantiFERON-Gold
• Any clinically significant skin lesions as described in Common Terminology Criteria for Adverse Events for Dermatology (CTCAE) Version 3.0
• ECG abnormalities at screening or randomization
• Evidence of organ dysfunction or hematopoietic disorder