Possible Interaction: Capsaicin and Clonidine

“In addition, they rated pain from intradermal capsaicin injections at a lumbar dermatome before and 60 min after clonidine injection and described areas of hyperalgesia and allodynia to mechanical stimuli.”

“By recording mEPSCs from large lamina I neurons in horizontal spinal cord slices the authors show that clonidine markedly reduces the frequency of mEPSCs induced by 500 nM capsaicin , with nearly no effect on the size of minis.”

“More recently, Campbell et al. reported that an increased pain response to capsaicin application is associated with a better treatment response to topical clonidine in painful diabetic neuropathy, presumably linking the capsaicin response to small fiber function ⇓.”

“As the capsaicin ratings increased, the magnitude of separation between the clonidine and placebo-treated groups became more pronounced.”

“The α2 agonists, clonidine (1 pM) and dexmedetomidine (1 pM) inhibited capsaicin currents, and yohimbine (1 nM) reversed the effects of clonidine.”

“Interestingly, the carotid vasodilator responses to capsaicin , but not those to alpha-CGRP or acetylcholine, were partially inhibited after clonidine (total dose: 24.4 microg/kg, i.v.);”

“These results suggest that clonidine inhibits the external carotid vasodilator responses to capsaicin by peripheral trigeminovascular and/or central mechanisms; this inhibitory response to clonidine seems to be predominantly mediated by alpha(2A)-adrenoceptors and, to a much lesser extent, by alpha(2C)-adrenoceptors.”

“The proportion of clonidine inhibited cells which responded to capsaicin increased 5 fold after injury.”

“ Clonidine (10−7M to 10−5M), morphine (10−6M), aspirin (10−3M), ketanserin (10−8M) and (±) …,345 (10−6M), an antagonist of neurokinin NK1 receptor, completely prevented the effects of capsaicin on the Kf,c. In contrast, terfenadine (10−7) … cimetidine (10−5M) had no protective effect against capsaicin.”

“2 The reflex fall in blood pressure following an intra‐arterial injection of capsaicin was partially blocked by an intrathecal infusion of clonidine (1 μg) at the spinal cord level L4‐L5, an effect which was abolished by the prior intrathecal infusion of yohimbine (5 μg).”