High-dose capsaicin patch reduces postherpetic neuralgia

A single, one hour-long application of a high-dose capsaicin patch recently approved by the Food and Drug Administration (FDA) not only proves to significantly reduce pain in patients suffering from postherpetic neuralgia, but also maintains its analgesic effect for up to three months.

The Qutenza patch (NeurogesX) is a novel medical treatment containing 8 percent capsaicin and is designed for the topical management of pain such as the neuropathic pain associated with postherpetic neuralgia.

The novelty of the device lies in the simplification of treatment of postherpetic pain, as a single application of the treatment can effect long-term analgesia without any of the adverse events commonly seen in other currently used therapies.

“The topical or oral treatments we currently use for postherpetic neuralgia all require a daily application or administration, sometimes up to three to four times a day. Qutenza, on the other hand, is only applied once for 60 minutes, achieving the same long-term analgesia,” says Mark Wallace, M.D., department of anesthesiology, University of California, San Diego.

Current therapies used to quell postherpetic pain include over-the-counter low-dose (0.025 to 0.075 percent) capsaicin-based patches and creams, opioids, pregabalin, gabapentin and a lidocaine patch.

According to Dr. Wallace, approximately 50 percent of patients will experience a 30 percent reduction in the pain associated with post-herpetic neuralgia with any of these treatment approaches. However, they require multiple daily dosing and/or application, which can prove cumbersome and tedious, underscoring one of Qutenza’s advantages.

Studying Qutenza
Dr. Wallace co-authored a study (Backonja M, Wallace M, et al. Lancet Neurol. 2008;7(12):1106-1112) evaluating the efficacy and safety of the Qutenza patch over a 12-week period. The multicenter, double-blind study included 402 participants with at least a six-month history of postherpetic neuralgia who were randomized to receive one-time 60-minute application of the 8 percent capsaicin-containing Qutenza patch (206 patients) or a low concentration 0.04 percent capsaicin-containing control patch (196 patients).

The primary efficacy endpoint was percentage change seen in numeric pain rating scale (NPRS) score from baseline to weeks two to eight. Patients were followed to week 12.

Results showed a significantly greater reduction in pain between weeks two and eight of treatment in those patients who received the Qutenza patch compared to controls. The mean changes in the NPRS scores from baseline to week eight were -29.6 percent versus -19.9 percent for the Qutenza and control group, respectively, which slightly improved by week 12.

A 30 percent or greater reduction in the mean NPRS score was seen in 87 patients (42 percent) and 63 patients (32 percent) of the Qutenza and control groups, respectively.

“Once the three months pass and the analgesic effect of the treatment begins to wear off, another treatment can simply be applied, if necessary, to further manage the pain. Repeat treatments with Qutenza have shown an efficacy out to 52 weeks,” Dr. Wallace says.

The adverse events with current treatment approaches can sometimes be difficult to tolerate and can include constipation, sedation and nausea with opioids, and cognitive impairment, vertigo and nausea with gabapentin and pregabalin. The lidocaine patch is a very well tolerated therapy and does not have any serious adverse events.

Side effects
Treatment with Qutenza proves to be safe with patients showing only mild-to-moderate and transient erythema and pain at the site of application. Transient blood pressure changes (less than 10 mm Hg) were also seen in study patients. However, these were associated with changes in pain level immediately after the application of the patch. There are no systemic toxicities with Qutenza and no systemic absorption of the drug.

“There is a distinct increase in pain at the target area where the patch is applied. Upon removing the patch after an hour, the pain will rapidly decrease. Most patients are not phased by and can easily tolerate this temporary increase in pain,” Dr. Wallace says.

After the painful target area is mapped, the patch is placed directly over this area for one hour. The capsaicin penetrates the dermis to activate a receptor on unmyelinated free nerve endings, resulting in an influx of calcium into the intracellular space. The massive influx initially depolarizes the nerves, resulting in transient pain followed by a prolonged desensitization of the nerve endings and prolonged pain relief.

A biopsy of the treated skin will demonstrate a regression of the epidermal unmyelinated nerve fibers. According to Dr. Wallace, this regression of the nerve fibers explains the long-lasting analgesic effect of locally applied capsaicin.

“Capsaicin in a way causes a chemodenervation where applied. These unmyelinated epidermal nerve fibers will regress and then regrow over the course of three to four months, at which time a new treatment with Qutenza may be required,” Dr. Wallace says. Qutenza, available on the market in the United States since May, requires a prescription.

Disclosures: Dr. Wallace has received research support from NeurogesX.