To investigate the effect of repeat oral dosing of CNV2197944 75 mg tid on the pain experienced in post-herpetic neuralgia (PHN) as measured by changes in PI-NRS after three weeks of treatment compared to the baseline period.

A 3 week randomised crossover study to investigate the effect of repeat oral dosing of CNV2197944 75 mg tid versus placebo for on the pain experienced in post-herpetic neuralgia (PHN. Each 3 week treatment period is seperated by a 2 week washout period. The primary outcome measure is the change from baseline in the PI-NRS after three weeks of treatment. Secondary outcome measures include pain responder rates, clinical and patient global impressions of pain, and the Neuropathic Pain Symptom Inventory.

Inclusion Criteria:

Male or female between 18 and 85 years of age inclusive, at the time of signing the informed consent.

Patients with post-herpetic neuralgia (PHN) with pain at screening present for more than 3 months after healing of the herpes zoster skin rash. The maximum duration of PHN will be no longer than 5 years.

Exclusion Criteria:

Patients having other severe pain, which may impair the self-assessment of the pain due to PHN.

Patients who have received nerve blocks for neuropathic pain within 4 weeks prior to the start of the single-blind placebo run-in Certain medications used to relieve the pain of PHN, specifically gabapentinoids (gabapentin and pregabalin), carbamazepine and topical agents (eg capsaicin, lidocaine) Patients with a documented failure to respond to a maximally tolerated dose regimen of gabapentin or pregabalin.

Patients taking more than one medication to treat the PHN pain