The purpose of this study is to evaluate the safety, effectiveness, and tolerability of 200 mg of RWJ-333369 given twice daily compared with placebo in the treatment of postherpetic neuralgia.

Postherpetic neuralgia is a distressing syndrome of neuropathic pain that continues for at least 3 months after the resolution of the varicella-zoster rash (shingles), can last up to years later, and for which therapies are often limited by incomplete pain relief and side effects. This is a randomized (study medication is assigned by chance), double-blind (neither the Investigator or the patient know the name of the assigned study medication), placebo-controlled, crossover, parallel-group, multicenter study to determine the effectiveness and safety of 200 mg of RWJ-333369 given twice daily for 4 weeks compared with placebo in patients with Postherpetic Neuralgia (PHN). The study hypothesis is that 200 mg of RWJ-333369 given twice daily for 4 weeks will be more effective than placebo in reducing pain due to PHN, as measured by average daily PHN pain scores. Patients will receive 200 mg of RWJ-333369 or matching placebo tablets, given in equally divided doses twice daily by mouth, with or without food, for 4 weeks in each of the 2 treatment periods.

Inclusion Criteria:

• Diagnosis of postherpetic neuralgia (PHN) with a history of varicella-zoster rash (shingles), persistent pain for at least 6 months after the healing of the rash
• Experienced postherpetic neuralgia pain on a daily basis for the past 3 months
• Women must be postmenopausal for at least 2 years, sexually abstinent, or if sexually active, be practicing an effective method of birth control, and have a negative serum pregnancy test at screening.

Exclusion Criteria:

• History of a poor response to 3 or more medications for postherpetic neuralgia (PHN), with poor response defined as treatment with medications in the following categories of therapy for at least 1 month at therapeutic dosages without at least moderate improvement, as judged by the study doctor: Antiepileptic drugs, antidepressants, serotonin norepinephrine uptake inhibitors (SNRIs), opioid analgesics, or lidocaine patch
• currently taking tricyclic antidepressants, Coumadin (warfarin), or continued treatment with an antiepileptic drug for any indication, Note: If taking these medications, to be eligible for the study, they must be tapered and discontinued
• past neurolytic treatment (destruction of nerves by the application of chemicals, heat or cold, neurosurgery, intrathecal pumps, or spinal cord stimulators for PHN pain
• currently using herbal topical creams or ointments for pain relief within 48 hours, capsaicin within 6 months, or systemic corticosteroids within 3 months of the baseline period
• Prior exposure to RWJ-333369 (carisbamate).