A Pilot Study to Compare Inhibitory Effects of Central Nervous System Drugs on Histamine-Induced Itch (Orinigal)

Histamine is a classic itch inducerand itch develops in a high percentage of subjects after a histamine skin prick. In this study we examined the antipruritic effects of ketamine (2 mg naloxone(0.2 mgand midazolam(1 mgon the histamine induced itch in 24 healthy male volunteers. Each drug was administered intravenously at subhypnotic doses before the histamine prick. Saline was intravenously injected as a negative controland azelastine was orally administered for three days as a positive control. Itch intensity was evaluated subjectively using a rating of 1 to 10 every minute until the sensation of itch disappeared. The drugs did not differ significantly in terms maximal itch intensityitch durationor the size of wheal and flare. However ketamine decreased itch intensity and duration somewhat. Because ketamine is a NMDA (N-methyl-D-aspartate receptor antagonist our results suggest NMDA might play a role in the central processing of histamine-induced itch. (Jikeikai Med J 2003;50:15-8