The starting point for this drug was the growing realization that eosinophils 
appeared to be associated with a severe form of asthma in which patients were 
subject to exacerbations of their condition that could not be adequately managed 
using inhaled and/or oral corticosteroids. Studies of the pathophysiology of 
eosinophils revealed that they produce many bioactive compounds that contribute 
to the pathophysiology of a number of diseases including asthma. Interleukin-5 
(IL-5) in particular is an important factor in some forms of severe asthma. A 
rat antibody to IL-5 (39D10) was humanized producing the product now know as 
reslizumab. However, initial studies of this antibody in patients with asthma 
were unsuccessful. It was only when the importance of the eosinophilic asthma 
endotype was recognized that reslizumab was found to indeed reduce the severity 
and exacerbations of asthma in patients who were inadequately treated by inhaled 
and/ or oral corticosteroids. These studies have determined that reslizumab is a 
valuable drug for the management of such patients provided that they have an 
eosinophil count of > 400 cells/mcL. Because a very small percentage of patients 
receiving reslizumab may experience anaphylaxis, reslizumab must be only given 
in a facility with adequate facilities and by a health professional trained in 
the management of anaphylaxis.