Safety and Efficacy of Gabapentin in Postherpetic Neuralgia

Inclusion Criteria:

1. Men or women 18 years or older who have experienced pain for at least 6 months, butnot more than 5 years after the healing of a herpes zoster skin rash(typically about 4months after the rash first appears).

2. Patient has a pain intensity score of at least 4 on the 11-point Numerical RatingScale (NRS). Patients should never be informed of the pain intensity criterion priorto screening or randomization.

3. Patients of child-bearing potential must have a negative serum pregnancy test atscreening and a negative follow-up urine pregnancy test at randomization.

4. Patient has a mean baseline week pain intensity score of at least 4 on the 11-pointNRS scale at the end of a 1-week baseline period and has completed at least 4 days ofdaily pain diary entries during the baseline week.

5. Patients must have a minimum washout period of greater than 5 times the half-life ofthe drug of several medications.

6. Patients currently treated with gabapentin pr pregabalin at screening may be eligiblefor the study, but must have a tapering period wherein the dose of gabapentin orpregabalin is reduced gradually over a period of 5 days followed by a two day washoutprior to the Baseline Week.

Exclusion Criteria:

1. Patients who have previously not responded to treatment for PHN with gabapentin orpregabalin.

2. Patients who previously experienced dose-limiting adverse effects that preventedtitration of gabapentin to an effective dose.

3. Patient is a nursing mother.

4. Patient has hypersensitivity to gabapentin.

5. Patient has had neurolytic or neurosurgical treatment for PHN.

6. Patient has severe pain from causes other than PHN.

7. Patient has used injected anesthetics or steroids within 30 days of baseline.

8. Patient has skin conditions in the area affected by the neuropathy that could altersensation.

9. Patient is in an immunocompromised state.

10. Patient has an estimated creatinine clearance less than 50 ml/min.

11. Patient has had malignancy within past 2 years other than basal cell carcinoma.

12. Patient has had gastric reduction surgery.

13. Patient has severe chronic diarrhea, chronic constipation [unless attributed to drugsthat will be washed out], uncontrolled irritable bowel syndrome (IBS) or unexplainedweight loss.

14. Patient has any abnormal chemistry or hematology results that are deemed by theinvestigator to be clinically significant.

15. Patient has a history of substance abuse within the past year.

16. Patient has a history of seizure (except for infantile febrile seizure) or is at riskof seizure due to head trauma.

17. Patient has a history of chronic hepatitis B or C, hepatitis within the past 3 months,or HIV infection.

18. Patient has any other clinically significant medical or psychological condition that,in the opinion of the Investigator would jeopardize the safety of the patient oraffect the validity of the study results.

19. Continuing use of any concomitant medication excluded by Inclusion Criterion 5.

20. Patient has participated in a clinical trial of an investigational drug or devicewithin 30 days of the screening visit.