PEPPERS AND PAIN - THE PROMISE OF CAPSAICIN

Capsaicin, the most pungent ingredient in red peppers, has been used f or centuries to remedy pain. Recently, its role has come under reinves tigation due to evidence that the drug acts selectively on a subpopula tion of primary sensory neurons with a nociceptive function. These neu rons, besides generating pain sensations, participate through an antid romic activation in the process known as neurogenic inflammation. The first exposure to capsaicin intensely activates these neurons in both senses (orthodromic:pain sensation; antidromic: local reddening, oedem a etc.). After the first exposure, the neurons become insensitive to a ll further stimulation (including capsaicin itself). This evidence led to the proposal of capsaicin as a prototype of an agent producing sel ective analgesia. This perspective is radically different from previou s 'folk medicine' cures, where the drug was used as a counter-irritati ng agent (i.e. for muscular pain). The new concept requires that capsa icin be repeatedly applied on the painful area to obtain the desensiti sation of the sensory neurons. Following this idea, capsaicin has been used successfully in controlling pain in postherpetic neuralgia, diab etic neuropathy and other conditions of neuropathic pain. Furthermore, evidence indicates that capsaicin could also control the pain of oste oarthritis. Finally, repeated applications of the drug to the nasal mu cosa result in the prevention of cluster headache attacks. On the basi s of this evidence, capsaicin appears to be a promising prototype for obtaining selective analgesia in localised pain syndromes.