A randomized vehicle-controlled trial of topical capsaicin in the treatment of postherpetic neuralgia.
A large double-blind, vehicle-controlled study of 143 patients with chronic postherpetic neuralgia (PHN) was performed to evaluate the degree of efficacy of topically applied capsaicin 0.075% cream. In addition, the safety and efficacy of long-term application of topical capsaicin in PHN was assessed by following patients in an open-label study for up to 2 years. In the double-blind phase, 143 patients with PHN of 6 months' duration or longer were enrolled. Since epidemiologic studies of patients who receive no treatment have shown that only 10% to 25% of those with PHN after 1 month will still have pain at 1 year, two separate efficacy analyses were performed: one with all evaluable patients (n = 131) and the other with 93 patients whose PHN lasted for longer than 12 months prior to study startup. All efficacy variables, including the physician's global evaluation of reduction in PHN pain, changes in pain severity on the categoric scale, visual analogue scale for pain severity, visual analogue scale for pain relief, and functional capacity scale, showed significant improvement at nearly all time points throughout the study for both patient groups, based on duration of PHN pain. In contrast, the group receiving vehicle cream remained essentially unchanged. Data from the long-term, open-label phase (up to 2 years, n = 77), which immediately followed the 6-week blinded phase, showed that the clinical benefit in patients treated for a short (6-week) period with topical capsaicin could be maintained or amplified in most patients (86%) during prolonged therapy. There were no serious adverse effects observed or reported throughout the trial; in fact, the only side effect associated with capsaicin treatment was the burning or stinging at local sites of application (in 9% of patients) during exposures of up to 2 years (long-term phase). On the basis of these data, we conclude that capsaicin 0.075% cream is a safe and effective treatment for the pain of postherpetic neuralgia and should be considered for initial management of patients with this condition.