A dermal patch that releases the experimental drug NGX-4010 for HIV-related distal sensory polyneuropathy (DSP), a painful condition caused by nerve damage, failed to perform better than a placebo in a phase III trial, according to NeurogesX, the developer of the compound. The results, reported in a February 27, 2008 press release from the company, stand in contrast to those from an earlier phase III trial suggesting that the patch alleviated pain for up to 12 weeks following a one-hour administration of the drug.

DSP may be caused by both HIV and some of the drugs used to treat it, such as Videx (didanosine) and Zerit (stavudine). The nerve damage that occurs can cause alternating tingling and pain, particularly in the extremities such as the feet and hands.

The most recent trial conducted by NeurogesX compared 494 HIV-positive people with DSP allotted to one of four groups. One group wore a patch containing NGX-4010 for 30 minutes and was compared with another group who wore a placebo patch for 30 minutes. A third group wore a patch with NGX-4010 for 60 minutes and was compared with a group that wore a placebo patch for 60 minutes. The participants’ degree of pain relief was evaluated at two weeks after administration and then 12 weeks after administration.

Overall, 29.5 percent of those in the treatment groups experienced pain relief, compared to 24.6 percent of those in the placebo groups. This difference was not statistically significant, meaning that the difference was small enough that it could have occurred by chance.

In its press release, NeurogesX explains that the treatment effect of those who received the drug in the study was similar to earlier studies, but that the treatment effect of those receiving placebo was much larger than was expected. The company intends to reanalyze data from earlier studies, where there was a difference in effect, to determine whether they have enough data to seek approval for the drug.