The goal of this clinical trial is to assess the efficacy and safety of Y-4 in patients with postherpetic neuralgia(PHN). The main questions it aims to answer are: The efficacy of Y-4 to treat PHN. If drug RK-4 is safe and tolerate in the patients with LHI? Researchers will analyze data from different groups, includes Y-4 group and pregabalin group , to see efficacy of Y-4 and If drug Y-4 is safe and tolerate in the patients with PHN. Participants will : * Take Y-4 (1w titration period:75 mg pregabalin +18.75 mg riluzole, 12w fixed dose period: 150 mg pregabalin +37.5 mg riluzole, 1w drug withdraw period: 1w titration period:75 mg pregabalin +18.75 mg riluzole) or pregabalin(75 mg for 1w titration period , 150 mg for 12w fixed dose period ,75 mg for 1w drug withdraw period) twice a day for 14 weeks after run-in period (placebo) lasting for 1 week. * Visit the hospital according to the follow-up schedule agreed upon with your doctor. contact the research staff as soon as possible to reschedule when unable to attend the scheduled study visit. * Use investigational products as directed by the doctor and undergo the related treatment. * Inform their investigators of any changes in their health, including any side effects or symptoms, whether or not they believe these changes are related to the trial medication, as well as any new medications they are using or wish to use, or any changes in the dosage of medications they have already taking. * Use reliable contraceptive methods , such as abstinence, intrauterine devices, double barrier methods (e.g., condom with spermicide or condom with a diaphragm containing spermicide), contraceptive implants, or oral contraceptives (except if the partner is infertile) during the study period and within one month after the study is completed. * Must inform investigators immediately if they or their partner become pregnant during the study. * Be sure to inform other doctors being consultant that you are participating in this clinical study. * Restrict medication use and treatment during the study.
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Evaluate the efficacy of Y-4 in patients with PHN by Change from baseline in Average Daily Pain Score (ADPS) for each group at week 13.
Timeframe: week 13