CROI: Capsaicin patch helps relieve neuropathy

A patch containing 8% capsaicin can relieve the pain caused by peripheral neuropathy for up to three months, according to a controlled study presented on Tuesday at the Thirteenth Conference on Retroviruses and Opportunistic Infections in Denver.

Peripheral neuropathy is the death of nerve cells in the extremities, particularly in the hands and feet. It produces numbness, tingling or pain, which can be severe. It is caused both by HIV and by certain HIV medications, such as ddI (didanosine, Videx / VidexEC), ddC (zalcitabine, Hivid) and d4T (stavudine, Zerit), nicknamed the ‘d’ drugs.

Around a third of HIV-positive people are estimated to suffer from peripheral neuropathy, which can severely diminish quality of life and lead to patients stopping their HIV medications.

Data presented by David Simpson of Mount Sinai School of Medicine in New York have shown that a patch containing 8% synthetic capsaicin can reduce pain in patients with HIV-associated peripheral neuropathy. The patch was only applied for up to 90 minutes before being removed, but the benefits of a single application were seen for up to twelve weeks.

Capsaicin is the ‘hot’ chemical produced in chilli peppers. Previous studies have shown that, when applied to the skin, it causes a local alleviation of pain by interfering with pain signalling mechanisms and causing the pain-sensitive nerves in the skin to die back temporarily.

Following promising results in a pilot study, investigators randomised 307 patients with neuropathy to receive the capsaicin patch or a control patch for 30, 60 or 90 minutes. Most of the participants were white men, with a mean pain score of 5.9 on a scale of zero to ten. Eighteen per cent of the patients were taking a ‘d’ drug as part of their anti-HIV treatment.

An anaesthetic cream was used to reduce the burning sensation caused by capsaicin, before the patch was applied to the affected areas on the feet. Control patients applied a low dose patch containing 0.04% capsaicin, designed to produce a short-lived local burning sensation without the longer-term pain relieving properties. At the end of the application period, the patch was removed and any remaining capsaicin cleaned off.

From two to twelve weeks after removal of the patch, the patients with the high-dose patch had a mean reduction of 23% in their pain score. This was greater than the pain reduction in the control group (11%, p = 0.003).

More patients in the high-dose group had a pain reduction of 30% or more (34 vs. 18%, p = 0.009).

When they broke down the data by the duration of patch application, the investigators found that the 30-minute group had a significantly greater pain reduction than the control patients (28%, p

However, three other validated pain scales showed similar rates of pain reduction across all three groups. This suggests that all three time periods produced effective pain reduction in the patients.

The patches were well tolerated, with only two (3%) of the patients in the 90-minute high-dose group removing the patch early. The patients were allowed to take painkillers during and after the treatment to control the burning sensation, but discomfort tended to resolve within three to five days.

The commonest side-effect of the patches was a reddening at the site of application. This was seen in 100 (44%) of the high-dose patch recipients, and 17 (21%) of the patients using the low-dose control patch.

Although the 8% patch is not yet commercially available, it may offer a more convenient approach to existing treatments for neuropathy related to HIV and other conditions such as diabetes. These include painkilling tablets, and lower-dose creams that need to be applied many times a day.

Follow-up of the patients in this study is continuing to examine the long-term effectiveness of the patch. A multinational trial is also being planned to confirm these findings, as are trials in diabetic and post-herpetic nerve pain.