The purpose of this study is to investigate whether NXN-462, a selective nNOS inhibitor, is effective in reducing pain levels in patients with post-herpetic neuralgia.

NXN-462 is designed to target the nitric oxide synthase system (NOS), specifically the neuronal NOS (nNOS) isoform. By design, NXN-462 is a potent inhibitor of nNOS with good affinity, and has little or no affinity for a range of G protein-coupled receptors, ion channels, and enzymes. NXN-462 is being developed as an oral therapy for the treatment of neuropathic pain syndromes, including PHN. This drug design strategy provides a new therapeutic paradigm for the treatment of chronic neuropathic pain.

Inclusion Criteria:

• Male, or a non-pregnant, non-lactating female 18 years or older
• Have voluntarily provided written informed consent
• able to speak, read, write, and understand English
• clinical diagnosis of PHN for a minimum of 6 months
• pain intensity score of ≥3 on a 0-10 Numerical Rating Scale (NRS) at the Screening Visit
• generally in good health (other than PHN) at Screening

Exclusion Criteria:

• Are pregnant and/or lactating
• Diagnosis of any chronic pain syndrome that would interfere with the assessment of PHN
• evidence of multiple causes of neuropathic pain,e.g.lumbar radiculopathy in the lumbosacral area
• Have had neuroablation or neurosurgical intervention for PHN
• Have been taking opioid analgesics for >5 days/week
• Have received nerve block or intrathecal analgesia within 6 weeks of the study
• History of significant gastrointestinal disease, liver disease, renal disease, endocrine disease, or cardiovascular disease
• clinically significant abnormal clinical laboratory test results or vital signs
• Are immunocompromised or immunosuppressed for any reason
• History of alcohol or other substance abuse (not including nicotine or tobacco) within 5 years
• Significant psychiatric disorder which requires drug treatment (except depression or anxiety treated with Selective Serotonin Re-uptake Inhibitors)
• Have received an investigational drug or have used an investigational device within 30 days of Screening.
• Have previously been randomized to this study