Influence of antihistamines, sedatives, and aspirin on experimental itch

Abstract

Experimental itch was elicited in volunteer patients by i.c. injection of histamine, trypsin (a protease releasing histamine) and papain (a protease not releasing histamine); itch duration and flare size were measured. The patients then received chlorcyclizine (an antihistamine with mild sedative effects), levomepromazine (an antihistamine with strong sedative effects), diazepam (a sedative without antihistamine action), aspirin (analgetic and anti inflammatory agent) or placebo, and experimental itch was again measured. It was found that the two antihistamines reduced the itch and the flare appearing after injection of histamine and trypsin; there was no difference between the two drugs in this respect, though levomepromazine caused marked sedation in contrast to chlorcyclizine. Papain produced no flare and the itch was not significantly altered by antihistamines. Diazepam did not reduce the itch produced by any agent. Aspirin increased the flare and tended to prolong the itch caused by histamine and trypsin. It is concluded that antihistamines inhibit histamine mediated itch but have no general antipruritic effect, and that sedatives (antihistamines or others) do not decrease experimental itch. Aspirin renders skin more sensitive to histamine; the reason for this is unknown.