The effect of terfenadine on dermographic wealing.

A double-blind comparison of terfenadine with placebo showed a reduction in potency of measured dermographic force-response of 67%, which is similar to that for inhibition of histamine weals by terfenadine. This and the parallel displacement of the force-response curves indicates that histamine is the main cause of dermographic wealing. Dermographic threshold and itch change together and appear to be the main determinant of the patients' subjective response. Dermographism relapsed towards its pre-treatment state during the 3 days after treatment was stopped. There was a small decrease in effect after administration of 60 mg b.d. for 47-84 days and a further small increase in response when the dose was increased to 120 mg t.d.s., but neither change was significant. None of the patients had a sedative response to the drug and terfenadine should prove useful in the treatment of wealing disorders.