Acute and latent leukopenic reaction to antipyrine

During the past 10 yr over 100 subjects received test doses of antipyrine in our laboratory for drug metabolism studies without any noticeable untoward effects. The present case describes an immediate allergic reaction to antipyrine and a latent leukopenic reaction 8 wk later without any drug exposure. Leukoagglutination was demonstrated in vitro following the addition of antipyrine, aminopyrine, phenylbutazone, or sulfinpyrazone to blood taken from the subject.