SR-419

Primary objective: To evaluate the efficacy of SR419 versus placebo in the treatment of PHN-related pain Secondary objectives: 1. To evaluate the efficacy of SR419 versus placebo in other pain assessment dimensions, treatment response, patient global impression of change (PGIC), sleep and related functions 2. To evaluate the safety and tolerability of SR419 in PHN patients 3. To evaluate the pharmacokinetic (PK) characteristics of SR419 and its metabolites in PHN patients Exploratory objectives: 1. To evaluate the relationship between the efficacy of SR419 in the treatment of PHN-related pain and the baseline quantitative sensory test (QST) parameters 2. To evaluate the onset time of SR419 in the treatment of PHN-related pain 3. To evaluate the duration of efficacy of SR419 in the treatment of PHN-related pain 4. Individualized evaluation of treatment effect by subjects