• Mean percent change from baseline in "average pain for the past 24 hours" NPRS score (i.e., average of scores during Weeks 12 and 48, compared to baseline).
  

• Proportion of subjects who score 2 or 3 ("Much Improved" or "Very Much Improved") on Patient Impression of Change at Weeks 12, 24, 36 and 48.
  
• Proportion of subjects with significant changes in concomitant pain medication usage during the 2nd through 12th week following study patch application.
  

Study C118 is a multicenter, open-label, single-arm study for subjects who successfully completed a previous NGX-4010 study and have not received open-label or blinded NGX-4010 study patches within the 12 weeks prior to study entry. One hundred eligible subjects will receive an initial open-label NGX-4010 study patch application and up to three additional open-label NGX-4010 applications at intervals of no less than 12 weeks, based on the presence or return of pain. Eligible subjects will have moderate to severe neuropathic pain secondary to HIV-AN or PHN, with average pain levels deemed appropriate for further treatment with NGX-4010 as judged by the Investigator.

Summary eligibility criteria:

• Subjects must be in good health and have successfully completed a past trial of NGX-4010 with no past occurrence of adverse events that would contraindicate further treatment.
• The time between the last study patch on the previous study and the first study patch on this study must be at least 12 weeks.
• Topical pain medications are exclusionary and require washout prior to study patch application for this study.
• Chronic, nontopical pain medications are allowed but must be stable (not as needed) for a defined period prior to first study patch application.
• Other specific inclusion and exclusion criteria must be met prior to enrollment on the study.