A limitation of this study is the small sample size, high
dropout rates, and missing data at some time points.
The pooling of results may partially alleviate this issue.
Due to the crossover design, many patients who received
the placebo during the first phase may have dropped out
due to lack of efficacy. Additionally, this trial was
interrupted and terminated due to the severe flood in
Thailand during study period. At that time, the hospital
was closed for several months and land transportation
was not possible. Nonetheless, the duration of the
evaluable treatment period (8 weeks) in this study was
appropriate to evaluate its efficacy. In general neuropathic
pain conditions, pain relief was experienced
within 6–12 weeks with a single application of 8%
capsaicin patch or repeated use of 0.075% capsaicin
cream.10 The frequency of application at 3–4 times a day
may also have contributed to noncompliance and
dropouts, but it reflected the real-life practice of this
topical preparation. However, the dropout rate due to
local side effect was low.
In summary, in this crossover study, we found that
topical preparation of capsaicin at 0.025% concentration
provided no significant benefit in providing pain
relief in patients with PDN, but it was safe and well
tolerated with minor skin reaction.