The purpose of this study is to evaluate the Efficacy and safety of pregabalin sustained release tablet versus placebo for postherpetic neuralgia.

This is a randomized, double-blind, multicenter, placebo-controlled trial to compare the efficacy and safety of pregabalin SR vs placebo in patients with PHN.

The study is conducting at 27 study centers in China. Patients were randomized to receive pregabalin, starting at 165 mg/day and increasing to a maintenance dose of 330 or 660 mg/day, or placebo.

The study includes a 1-week, single-blind, placebo run-in period; a 2-week dose-escalation/optimization phase; a 12-week, fixed-dose treatment period; and a 1-week taper phase.

Inclusion Criteria:

1. Outpatient ，Patients can not stay in the hospital overnight；
2. Patients must have pain present for more than 3 months after the healing of the herpes zoster skin rash；
3. At least 4 days and at least 8 pain diaries(Pain Numeric Rating Scale) must be completed satisfactorily within the seven days of single-blind, placebo run-in period, and the average pain score must be greater than or equal to 4；
4. At screening (V0) and enrollment (V1), patients must have a score of greater than or equal to 40 mm on the 100 mm pain visual analog scale；
5. Women were neither pregnant nor lactating, and those of childbearing age had a confirmed negative serum pregnancy test at baseline and practiced an appropriate method of contraception throughout the study.

Exclusion Criteria:

1. Decrease of ≥30% on their pain VAS or ≥ 4 between any two pain diaries during the placebo run-in period.( in order to remove potential placebo-responders)；
2. Patients who had failed to respond to previous treatment for PHN with gabapentin at doses ≥1200 mg/day ；
3. History of using pregabalin or participation in a previous trial of pregabalin；
4. Patients with a skin condition or severe non-PHN pain that might impair the self assessment of pain caused by PHN；
5. Patients with other Nervous system disorders which might impair completing the pain diaries or sleep interference diaries；
6. History of epilepsy and being treated by drug therapy；
7. Previous surgical therapy for PHN；
8. History of using effective therapies during 2 weeks before screening (V0),eg: acupuncture and moxibustion, Transcutaneous Electrical Nerve Stimulation；
9. Potentially retinal toxicity of drugs past or now；
10. Prohibited medications without appropriate washout；
11. Malignancy within the past 2 years；
12. Laboratory examination: WBC<2.5×109/L；ANC<1.5×109/L；PLT<100×109/L；ALT/AST>3ULN；
13. Creatinine clearance ≤ 60 mL/min；
14. Positive antibody of Hepatitis c，Human immunodeficiency virus ，Treponema pallidum ；
15. Patients who are allergic to or intolerant of pregabalin or other drugs which have a similarly chemical structure ；
16. History of illicit drug or alcohol abuse within the last 2 years；
17. Clinically significant or unstable hepatic, respiratory, or hematologic illnesses or psychologic conditions; unstable cardiovascular disease which may increase the risk of participation the clinical trial in the opinion of the study investigator.