Successful challenge with clozapine in a history of eosinophilia

Eosinophilia has been encountered from 0.2 to 61.7% in clozapine-treated patients, mostly with a transient course and spontaneous remission. There have been few reports, however, which have investigated a challenge with clozapine in patients previously showing eosinophilia. Two case reports are presented: the first with clozapine challenge after eosinophilia, the second under clozapine treatment and no previous haematological side effects. The challenge case showed eosinophilia with 1.2 10(9)/l (z = 1.79, p = 0.04) being followed by normalization despite clozapine continuation, whereas the maximum value reached 2.1 10(9)/l in the single episode case, with consecutive normalization and uninterrupted treatment. Eosinophilia caused by clozapine was observed in challenge, preceded by a faster neutrophil production and consecutive decrease (z = 2.27, p = 0.01). A challenge with clozapine was feasible and showed no clinical symptoms of eosinophilia.