Transdermal clonidine versus placebo in painful diabetic neuropathy

In a randomized, double-blind, 2-period crossover study, 24 patients with pain due to diabetic polyneuropathy received transdermal clonidine, 0.3 mg/day, and placebo patches, each for 6 weeks. Pain was assessed daily by a 13-word descriptor list. Mean daily pain scores for the 6th week, the primary outcome variable, averaged 13% lower with clonidine than with placebo (95% conf. lim. for clonidine effect: 29% reduction to 3% increase in pain), which was not statistically significant (P = 0.11, 2-tailed paired t test). After this study, however, 9 patients who wished to continue clonidine had single (3 patients) or multiple (6 patients) cycles of clonidine withdrawal and rechallenge. Seven of 9 patients consistently reported return of pain with patch withdrawal followed by relief upon retreatment. One patient had an equivocal response, and the other patient had no relief upon retreatment. The 7 responders appeared similar to the other 17 patients in pain quality and neurological exam. We conclude that there may be a subset of patients with diabetic polyneuropathy who respond to transdermal clonidine. Further research is needed to identify features of neuropathic pain that predict drug response and to develop study designs that are more sensitive to a response in a subset of patients.