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Summary Background The limitations of current treatments for postherpetic neuralgia (PHN) have led to the investigation of localised, non-systemic alternatives. NGX-4010, a high-concentration (8%) capsaicin dermal patch, was developed to treat patients with neuropathic pain. We report the results of a randomised, double blind, 12-week study of the efficacy and safety of one application of NGX-4010 in patients with PHN. Methods In this multicentre, double-blind, parallel-group trial, 402 patients were randomly assigned to one 60-min application of NGX-4010 (640 μg/cm 2 [8% capsaicin]) or a low-concentration capsaicin control patch (3·2 μg/cm 2 [0·04% capsaicin]). Patients were aged 18–90 years, had had postherpetic neuralgia for at least 6 months, and had an average baseline numeric pain rating scale (NPRS) score of 3 to 9. The primary efficacy endpoint was percentage change in NPRS score from baseline to weeks two to eight. Analysis was by intention to treat. This trial is registered with ClinicalTrials.gov, number NCT00115310. Findings Patients who were randomly assigned to NGX-4010 (n=206) had a significantly greater reduction in pain during weeks two to eight than did patients who had the control patch (n=196). The mean changes in NPRS score were −29·6% vs −19·9% (difference −9·7%, 95% CI −15·47 to −3·95; p=0·001). 87 (42%) patients who received NGX-4010 and 63 (32%) controls had a 30% or greater reduction in mean NPRS score (odds ratio [OR] 1·56, 95% CI 1·03 to 2·37; p=0·03). The patients who had NGX-4010 had significant improvements in pain during weeks two to 12 (mean change in NPRS score −29·9% vs −20·4%, difference −9·5, −15·39 to −3·61; p=0·002). Transient blood pressure changes associated with changes in pain level were recorded on the day of treatment, and short-lasting erythema and pain at the site of application were common, self-limited, and generally mild to moderate in the NGX-4010 group and less frequent and severe in the controls. Interpretation One 60-min application of NGX-4010 provided rapid and sustained pain relief in patients with postherpetic neuralgia. No adverse events were associated with treatment except for local reactions at the site of application and those related to treatment-associated pain. Funding NeurogesX.

Objectives To evaluate the efficacy, safety, and tolerability of repeated NGX-4010 treatments in the open-label extension phase of a 52-week study in patients with neuropathic pain due to HIV-associated distal sensory polyneuropathy (HIV-DSP). Methods Patients completing the 12-week, randomized, double-blind phase of the study could enter a 40-week, open-label phase, and receive up to 3, 60-minute NGX-4010 treatments. Patients recorded their "average pain for the past 24 hours" daily using the Numeric Pain Rating Scale (NPRS). Efficacy assessment included the percentage NPRS score reduction from baseline to weeks 2 to 12 after the final treatment, and Patient Global Impression of Change (PGIC) and Clinician Global Impression of Change (CGIC) questionnaires at study termination. Results Of 307 patients randomized, 272 entered the open-label phase; 81, 90, 55, and 46 received 0, 1, 2, and 3 retreatments, respectively. The mean percentage decrease in NPRS score from baseline to weeks 2 to 12 after the final treatment was similar in patients receiving single or multiple NGX-4010 treatments (-25.8%, -27.1%, -24.6%, and -22.7% for 1, 2, 3, and 4 NGX-4010 treatments, respectively). PGIC and CGIC results demonstrated a benefit of NGX-4010 treatment through to the end of the study regardless of the number of treatments received. Transient local application site reactions were the most frequently reported adverse events, and were mainly mild to moderate, nonserious, and did not increase with repeated treatment. Discussion Repeated NGX-4010 treatments were generally well tolerated and resulted in consistent reductions in HIV-DSP-associated pain and improvement in patient-reported outcomes.