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 and safety of Y-4 to treat PHN compared with pregabalin.

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.

Inclusion Criteria:

- 1. Able to understand and voluntarily sign the informed consent form. 2. Age ≥ 18 years, any gender. 3. Diagnosed with PHN, meaning pain persists for more than one month after the acute shingles rash has healed.

4. VAS score in SF-MPQ ≥ 40 mm of the last 24 hours during screening.

Exclusion Criteria:

• 1. Known previous allergy to the investigational products, rescue medication ingredients, other chemically similar drugs, or excipients.

  2. During screening, individuals who have been clearly diagnosed with peripheral neuropathy or pain unrelated to PHN (including but not limited to those caused by cerebrovascular disease, Guillain-Barré syndrome, cervical or lumbar spine disorders, osteoarticular or tendon lesions, chronic kidney disease or uremia, thyroid disease, intracranial tumors, trauma, etc.) and are judged by the investigator to potentially confound the assessment of PHN.

  3. During screen, suffer from a systemic disease that, in the opinion of the investigator, may affect the patient's participation in the study or affect the evaluation of the efficacy of PHN, including but not limited to:

  1. Severe cardiopulmonary diseases, such as unstable angina, myocardial infarction, severe arrhythmia within 6 months prior to screening, NYHA cardiac function classification of grade III~IV at screening, hypertension (systolic blood pressure > 160 mmHg or diastolic blood pressure > 100 mmHg at screening), recurrent asthma attacks, etc.;
  2. Chronic digestive diseases, such as liver fibrosis, chronic active hepatitis, peptic ulcer, etc.;
  3. Neuropsychiatric disorders, including epilepsy, recurrent dizziness or headache, cognitive impairment; Cerebrovascular disease (such as cerebral infarction) or recurrent transient ischemic attack within 6 months prior to screening;
  4. History of malignant tumors within 5 years prior to screening (excluding cured basal cell carcinoma of the skin, carcinoma in situ and papillary thyroid carcinoma);
  5. Presence of active infection, which, in the opinion of the investigator, is not suitable for entry into this study;
  6. Diabetic patients with poor glycemic control (peritoneal venous blood glucose ≥11mmol/L at screening);
  7. Suffering from immunocompromised diseases, such as systemic lupus erythematosus, acquired immunodeficiency syndrome, immunosuppressant therapy for autoimmune diseases.

  4. During screening, situations may exist that investigators believe could affect pain assessment, such as if the affected skin area has a skin condition that may influence sensation.

  5. Previously received nerve destruction for PHN, or underwent minimally invasive interventions (such as nerve blocks or neurostimulation), physical therapy (such as red light therapy), or traditional Chinese external treatments (such as acupuncture) within one week prior to screening.

  6. Use prohibited drugs within the first 5 half-lives, or change the restricted drug dosage within the first 14 days.

  7. Severe hematological, hepatatological, and renal function abnormalities at the time of screening, which meet any of the following laboratory test results: 1) Hematology: neutrophil count < 1.5×109/L, or platelet < 90×109/L, or hemoglobin <100g/L; 2) Liver function: ALT or AST > 2.5 times ULN; or TBIL > 1.5 times ULN; 3) Renal function: CrCL<60 mL/min/1.73 m2 (calculated based on Cockroft-Gault formula a); 4) Creatine kinase >2-fold ULN.

  8. Participants already diagnosed with sleep apnea, or those with severe snoring and daytime sleepiness, as well as intermittent hypoxia.

  9. Participants with a history of suicidal behavior, or those assessed to have suicidal tendencies using the Columbia-Suicide Severity Rating Scale (C-SSRS).

  10.Hepatitis B surface antigen (HBsAg) positive and HBV-DNA titer >lower limit of reference value, or hepatitis C virus antibody (HCV-Ab) positive and HCV-DNA titer >lower limit of reference value, or human immunodeficiency virus antibody (HIV-Ab) positive, or serum Treponema pallidum-specific antibodies (TP-Ab) positiv eand rapid plasma reagin/toluidine red unheated serum test (RPR or TRUST) positive at screening.

  11. Known drug abuse, or history of alcohol abuse within 1 year prior to screening, i.e., drinking more than 14 units of alcohol per week (1 unit = 360 mL of beer or 45 mL of spirits with 40% alcohol or 150 mL of wine).

  12. Pregnant or lactating females. 13.Male (or their partner) or female subjects have a fertility plan during the whole study period and within 1 month after the end of the study or are unwilling to take one or more non-drug contraceptive measures (such as condoms, intrauterine devices, etc.) during the study period.

  14.Prior participation in any other clinical study of any other drug within 30 days prior to screening.

  15.Engaging in high-altitude work, driving motor vehicles, or operating heavy machinery with associated risks during the study period.

  16.Other conditions that are considered unsuitable by the investigator to participate in this clinical study.