The purpose of this study is to assess the painkilling efficacy of ASP8477 relative to mock (placebo) in patients that have been diagnosed with painful diabetic peripheral neuropathy or postherpetic neuralgia determined by the change in the average daily pain intensity in patients that initially respond favorably to treatment with ASP8477.

The study will consist of a Screening Period, Single-Blind Treatment Period, Double-Blind Randomized Withdrawal Period and Follow-up Period.

Inclusion Criteria:

• PDPN subject must have:

  • Established diagnosis of diabetes (type I or II) with painful diabetic peripheral neuropathy and glycosylated hemoglobin (HbA1c) ≤ 11% at Screening.
  • Stable glycemic control (HbA1c ≤ 11%) achieved by a drug regimen for at least 3 months prior to Screening.
  • At least a 1-year history of DPN pain.
  • Diabetic distal symmetrical polyneuropathy symptoms (including pain) stable for at least the last 3 months prior to Screening based on PI judgment and subject-reported medical history.

• PHN subject must have pain present ≥ 6 months after healing of the herpes zoster rash.

Exclusion Criteria:

• Subject has significant pain of an etiology other than PDPN or PHN, or clearly non differentiated pain, or plantar fasciitis, heel spurs, tibial neuropathy, Morton's neuroma, bunions, metatarsalgia, arthritis in feet, ischemic pain, neurological disorders unrelated to diabetic neuropathy, skin condition in area of neuropathy that could alter sensation, malignancy, or current orthostatic hypotension, hypo or hypertension, syncope or clinically significant ECG, clinical intolerance to Non-steroidal anti-inflammatory drugs (NSAIDs) or ASP8477, depression, psychosis or psychiatric or neurological illness, BMI of over 35, renal impairment or failure, alcohol (ETOH) or drug abuse, GI complaints.
• Previous investigational therapy within 28 days or 5 half lives