The objective of the trial is to investigate the analgesic efficacy of SPM 927 in subjects with moderate to severe neuropathic pain due to Postherpetic Neuralgia (PHN)

Inclusion Criteria:

• Subject has clinically diagnosed painful postherpetic neuralgia present at least six months after healing of a herpes zoster skin rash and has at least one form of allodynia
• Subject must have at least moderate pain (mean pain intensity ≥ 4 out of 10 during the baseline week on Likert scale).

Exclusion Criteria:

• Subject has other conditions that cause pain at least as severe as the postherpetic neuralgia.
• Subject has had any surgical treatment or any neurolytic injections for PHN
• Subject has clinically significant ECG and laboratory abnormalities.
• Subject is receiving treatment with anti-epileptic drugs (AEDs), muscle relaxants, mexiletine, topical analgesics, antidepressants, opioids, non-steroidal anti-inflammatory drugs (NSAIDs), paracetamol, benzodiazepines, and antiviral agents.
• Subject has liver function tests (AST, ALT, alkaline phosphatase, total bilirubin and GGT out of the reference range) > 1,5 x ULN (upper limit of normal) at visit 1
• Subject has serum creatinine ≥ 2 times the upper limit of reference range at Visit 1.