Suppressive effects of transdermal clonidine administration on contact hypersensitivity reactions in guinea pigs

In the present study, immunopharmacological effects of clonidine-TTS on allergic contact dermatitis (ACD) to non-related, established contact sensitizers were investigated in guinea pigs. First, to evaluate the hypotensive effect of clonidine-TTS in guinea pigs, intra-arterial blood pressure was recorded. After 4 days of treatment with one (or two) TTS per animal, a reduction of arterial blood pressure from 71 +/- 1 to 51 +/- 2 mm Hg was observed. We subsequently assessed the effects of clonidine-TTS on contact hypersensitivity reactions to 2,4-dinitrochlorobenzene (DNCB) and 4-ethoxymethylene-2-phenyl-oxazolone (Ox). This study indicates that clonidine-TTS suppressed the elicitation of contact hypersensitivity reactions. The observed immunosuppressive effect of clonidine may account for the relatively weak hypersensitivity reactions to this drug in experimental animal studies. Further studies are needed to determine whether such findings are of relevance to the clinical use of clonidine in patient populations.