Alpha-fluoromethylhistidine in the treatment of idiopathic cold urticaria

Alpha-fluoromethylhistidine (alpha-FMH), a new irreversible inhibitor of mammalian histidine decarboxylase, was tested in the treatment of idiopathic cold urticaria in 11 patients. In the initial trial with 50 mg b.i.d., a significant decrease (about 30%) in the total blood histamine level was found after 3 weeks of treatment but clinically there was no improvement in the symptoms of ten cold urticaria patients nor in the responses to the ice-cube test. In the second trial with three patients suffering from severe idiopathic cold urticaria, a higher dose of up to 500 mg b.i.d. of alpha-FMH for 3 weeks resulted in a marked decrease in the total blood histamine level as well as in an apparent inhibition of histamine synthesis in the skin previously exposed several times to cold water. The symptoms of cold urticaria and the responses in the ice-cube tests also decreased simultaneously. No clinical side effects nor changes in laboratory analysis were seen during the treatment with alpha-FMH. These results suggest that alpha-FMH may be useful in the treatment of severe cold urticaria especially in combination with histamine exhaustion of mast cells using cold water.